view Side-By-Side changes
IETF Mobile IP Working Group David B. Johnson
INTERNET-DRAFT Carnegie Mellon University
Charles Perkins
Sun Microsystems
13 March
4 August 1998
Mobility Support in IPv6
<draft-ietf-mobileip-ipv6-05.txt>
<draft-ietf-mobileip-ipv6-06.txt>
Status of This Memo
This document is a submission by the Mobile IP Working Group of the
Internet Engineering Task Force (IETF). Comments should be submitted
to the Working Group mailing list at "mobile-ip@SmallWorks.COM".
Distribution of this memo is unlimited.
This document is an Internet-Draft. Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas,
and its working groups. Note that other groups may also distribute
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at
any time. It is inappropriate to use Internet-Drafts as reference
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To view the entire list of current Internet-Drafts, please check
the "1id-abstracts.txt" listing contained in the Internet-Drafts
Shadow Directories on ftp.is.co.za (Africa), ftp.nordu.net (Europe),
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Abstract
This document specifies the operation of mobile computers using IPv6.
Each mobile node is always identified by its home address, regardless
of its current point of attachment to the Internet. While situated
away from its home, a mobile node is also associated with a care-of
address, which provides information about the mobile node's current
location. IPv6 packets addressed to a mobile node's home address are
transparently routed to its care-of address. The protocol enables
IPv6 nodes to cache the binding of a mobile node's home address with
its care-of address, and to then send any packets destined for the
mobile node directly to it at this care-of address.
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Contents
Status of This Memo i
Abstract i
1. Introduction 1
2. Comparison with Mobile IP for IPv4 3
3. Terminology 4 6
3.1. General Terms . . . . . . . . . . . . . . . . . . . . . . 4 6
3.2. Mobile IPv6 Terms . . . . . . . . . . . . . . . . . . . . 5 7
3.3. Specification Language . . . . . . . . . . . . . . . . . 6 8
4. Overview of Mobile IPv6 7 9
4.1. Basic Operation . . . . . . . . . . . . . . . . . . . . . 7 9
4.2. New IPv6 Destination Options . . . . . . . . . . . . . . 9 11
4.3. Conceptual Data Structures . . . . . . . . . . . . . . . 11 13
4.4. Binding Management . . . . . . . . . . . . . . . . . . . 14 16
5. New IPv6 Destination Options 16 19
5.1. Binding Update Option Format . . . . . . . . . . . . . . 16 19
5.2. Binding Acknowledgement Option Format . . . . . . . . . . 20 23
5.3. Binding Request Option Format . . . . . . . . . . . . . . 24 27
5.4. Home Address Option Format . . . . . . . . . . . . . . . 25 28
6. Modifications to IPv6 Neighbor Discovery 27 30
6.1. Modified Router Advertisement Message Format . . . . . . 30
6.2. Modified Prefix Information Option Format . . . . . . . 27
6.2. . 31
6.3. New Advertisement Interval Option Format . . . . . . . . 33
6.4. New Home Agent Information Option Format . . . . . . . 28
6.3. . 34
6.5. Changes to MinRtrAdvInterval Limits Sending Router Advertisements . . . . . . . . 36
6.6. Changes to Sending Router Solicitations . . . . . . . . . 29 37
7. Requirements for IPv6 Nodes 30 39
7.1. Requirements for All IPv6 Hosts and Routers . . . . . . . 30 39
7.2. Requirements for All IPv6 Routers . . . . . . . . . . . . 39
7.3. Requirements for IPv6 Home Agents . . . . . . . . . . . . 30
7.3. 39
7.4. Requirements for IPv6 Mobile Nodes . . . . . . . . . . . 31 40
8. Correspondent Node Operation 32 42
8.1. Receiving Packets from a Mobile Node . . . . . . . . . . 32 42
8.2. Receiving Binding Updates . . . . . . . . . . . . . . . . 32 42
8.3. Requests to Cache a Binding . . . . . . . . . . . . . . . 33 43
8.4. Requests to Delete a Binding . . . . . . . . . . . . . . 34 44
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8.5. Sending Binding Acknowledgements . . . . . . . . . . . . 34 44
8.6. Sending Binding Requests . . . . . . . . . . . . . . . . 34 45
8.7. Cache Replacement Policy . . . . . . . . . . . . . . . . 35 45
8.8. Receiving ICMP Error Messages . . . . . . . . . . . . . . 36
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8.9. Sending Packets to a Mobile Node . . . . . . . . . . . . 37 47
9. Home Agent Operation 39 49
9.1. Receiving Router Advertisement Messages . . . . . . . . . 39 49
9.2. Dynamic Home Agent Address Discovery . . . . . . . . . . 39 50
9.3. Primary Care-of Address Registration . . . . . . . . . . 40 51
9.4. Primary Care-of Address De-registration . . . . . . . . . 43 54
9.5. Intercepting Packets for a Mobile Node . . . . . . . . . 54
9.6. Tunneling Intercepted Packets to a Mobile Node . . . . . 44
9.6. 56
9.7. Renumbering the Home Subnet . . . . . . . . . . . . . . . 44 57
10. Mobile Node Operation 46 60
10.1. Sending Packets While Away from Home . . . . . . . . . . 46 60
10.2. Receiving Packets While Away from Home . . . . . . . . . 62
10.3. Movement Detection . . . . . . . . . . . . . . . . . . . 48
10.3. 63
10.4. Forming New Care-of Addresses . . . . . . . . . . . . . . 50
10.4. 66
10.5. Sending Binding Updates to the Home Agent . . . . . . . . 51
10.5. 67
10.6. Dynamic Home Agent Address Discovery . . . . . . . . . . 68
10.7. Sending Binding Updates to Correspondent Nodes . . . . . 53
10.6. 69
10.8. Sending Binding Updates to the Previous Default Router . 55
10.7. 71
10.9. Retransmitting Binding Updates . . . . . . . . . . . . . 55
10.8. 72
10.10. Rate Limiting for Sending Binding Updates . . . . . . . . 56
10.9. 72
10.11. Receiving ICMP Error Messages Binding Acknowledgements . . . . . . . . . . . 72
10.12. Receiving Binding Requests . . . 56
10.10. Receiving Binding Acknowledgements . . . . . . . . . . . 57
10.11. Receiving Binding Requests . 73
10.13. Receiving ICMP Error Messages . . . . . . . . . . . . . . 58
10.12. 74
10.14. Receiving Tunneled Router Advertisements . . . . . . . . 74
10.15. Using Multiple Care-of Addresses . . . . . . . . . . . . 58
10.13. 75
10.16. Routing Multicast Packets . . . . . . . . . . . . . . . . 58
10.14. 76
10.17. Returning Home . . . . . . . . . . . . . . . . . . . . . 59 76
11. Constants 61 78
12. IANA Considerations 62 79
13. Security Considerations 63 80
13.1. Binding Updates, Acknowledgements, and Requests . . . . . 63 80
13.2. Home Address Options Option . . . . . . . . . . . . . . . . . . 63 . 80
13.3. General Mobile Computing Issues . . . . . . . . . . . . . 64 81
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Changes from Previous Draft 66 83
Acknowledgements 68 85
References 69 86
Chair's Address 71 88
Authors' Addresses 72 89
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1. Introduction
This document specifies the operation of mobile computers using
Internet Protocol Version 6 (IPv6) [5]. Without specific support
for mobility in IPv6, packets destined to a mobile node (host or
router) would not be able to reach it while the mobile node is away
from its home link (the link on which its home IPv6 subnet prefix is
in use), since routing is based on the subnet prefix in a packet's
destination IP address. In order to continue communication in spite
of its movement, a mobile node could change its IP address each time
it moves to a new link, but the mobile node would then not be able
to maintain transport and higher-layer connections when it changes
location. Mobility support in IPv6 is particularly important, as
mobile computers are likely to account for a majority or at least a
substantial fraction of the population of the Internet during the
lifetime of IPv6.
The protocol operation defined here, known as Mobile IPv6, allows a
mobile node to move from one link to another without changing the
mobile node's IP address. A mobile node is always addressable by
its "home address", an IP address assigned to the mobile node within
its home subnet prefix on its home link. Packets may be routed to
the mobile node using this address regardless of the mobile node's
current point of attachment to the Internet, and the mobile node may
continue to communicate with other nodes (stationary or mobile) after
moving to a new link. The movement of a mobile node away from its
home link is thus transparent to transport and higher-layer protocols
and applications.
The Mobile IPv6 protocol is just as suitable for mobility across
homogeneous media as for mobility across heterogeneous media. For
example, Mobile IPv6 facilitates node movement from one Ethernet
segment to another as well as it facilitates node movement from an
Ethernet segment to a wireless LAN cell, with the mobile node's IP
address remaining unchanged in spite of such movement.
One can think of the Mobile IPv6 protocol as solving the "macro"
mobility management problem. More "micro" mobility management
applications -- for example, handoff among wireless transceivers,
each of which covers only a very small geographic area -- are
possibly more suited to other solutions. For example, in many
current wireless LAN products, link-layer mobility mechanisms allow a
"handoff" of a mobile node from one cell to another, reestablishing
link-layer connectivity to the node in each new location. As long
as such handoff occurs only within cells of the mobile node's home
link, such link-layer mobility mechanisms are likely to offer faster
convergence and lower overhead than Mobile IPv6. Extensions to the
Mobile IPv6 protocol are also possible to support a more local,
hierarchical form of mobility management, but such extensions are
beyond the scope of this document.
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The protocol specified in this document solves the problem of
transparently routing packets to and from mobile nodes while away
from home. However, it does not attempt to solve all general
problems related to the use of mobile computers or wireless networks.
In particular, this protocol does not attempt to solve:
- Handling links with partial reachability, such as typical
wireless networks. Some aspects of this problem are addressed
by the movement detection procedure described in Section 10.2, 10.3,
but no attempt has been made to fully solve this problem in its
general form. Most aspects of this problem can be solved by the
workaround of restricting such networks to only one router per
link, although there are still possible hidden terminal problems
when two nodes on the same link (on opposite sides of the router)
attempt to communicate directly.
- Access control on a link being visited by a mobile node. This
is a general problem any time an untrusted node is allowed
to connect to any link layer. It is independent whether the
connecting node uses Mobile IP, DHCP [2], or just "borrows" an IP
address on the link.
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2. Comparison with Mobile IP for IPv4
[This section will include
The design of Mobile IP support in IPv6 (Mobile IPv6) represents a comparison between
natural combination of the experiences gained from the development
of Mobile IP support in IPv4 (Mobile IPv4) [15, 14, 16], together
with the opportunities provided by the design and deployment of a new
version of IP itself (IPv6) and the new protocol features offered
by IPv6. Mobile IPv6 thus shares many features with Mobile IPv4,
but the protocol is now fully integrated into IP and provides many
improvements over Mobile IPv4. This section summarizes the major
differences between Mobile IPv4 protocol [13, 12, 14]. However, this
comparison has not yet been written. It will be filled in with the
next revision to this draft.]
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- Support for what is known in IPv6 13 March 1998
3. Terminology
3.1. General Terms
IP
Internet Protocol Version 6 (IPv6).
node
A device that implements IP.
router
A node that forwards IP packets not explicitly addressed to
itself.
host
Any node that Mobile IPv4 as "Route
Optimization" [17] is not now built in as a router.
link
A communication facility or medium over which nodes can
communicate at fundamental part
of the link layer, such protocol, rather than being added on as an Ethernet (simple or
bridged). A link is the layer immediately below IP.
interface
A node's attachment to a link.
subnet prefix
A bit string that consists of some number optional
set of initial bits extensions that may not be supported by all nodes
as in Mobile IPv4. This integration of an
IP address.
interface identifier
A number used Route Optimization
functionality allows direct routing from any correspondent node
to identify a any mobile node, without needing to pass through the mobile
node's interface on a link. The
interface identifier is home network and be forwarded by its home agent, and thus
eliminates the remaining low-order bits problem of "triangle routing" present in the
node's IP address after base
Mobile IPv4 protocol [15]. This integration also allows the subnet prefix.
link-layer address
A link-layer identifier for an interface, such as IEEE 802
addresses on Ethernet links.
packet
An IP header plus payload.
Johnson
Mobile IPv4 "registration" functionality and Perkins Expires 13 September 1998 [Page 4]
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Route Optimization functionality to be performed by a single
protocol rather than two separate (and different) protocols.
- Support in IPv6 13 March 1998
3.2. is also integrated into Mobile IPv6 Terms
home address
An -- and into IPv6
itself -- for allowing mobile nodes and Mobile IP address assigned to a coexist
efficiently with routers that perform "ingress filtering" [6]. A
mobile node within now uses its home link.
home subnet prefix
The care-of address as the Source Address in
the IP subnet prefix corresponding header of packets it sends, allowing the packets to a mobile node's home
address.
home link pass
normally through ingress filtering routers. The link on which a mobile node's home subnet prefix is
defined. Standard IP routing mechanisms will deliver packets
destined for a mobile node's home address to its home link.
of the mobile node
A node that can change its point of attachment from one link to
another, while still being reachable via its home address.
movement
A change is carried in the packet in a mobile node's point Home Address
destination option, allowing the use of attachment to the Internet
such that it is no longer connected to care-of address in
the same link as it was
previously. If a mobile node is not currently attached packet to its
home link, be transparent above the mobile node is said IP layer. The ability
to be "away from home".
correspondent node
A peer node with which correctly process a mobile node Home Address option in a received packet
is communicating. The
correspondent node may be either required in all IPv6 nodes, whether mobile nor stationary,
whether host or stationary.
foreign subnet prefix
Any IP subnet prefix other than router.
- The use of the mobile node's home subnet
prefix.
foreign link
Any link other than care-of address as the mobile node's home link.
home agent
A router on Source Address in each
packet's IP header also simplifies routing of multicast packets
sent by a mobile node's home link with which node. With Mobile IPv4, the mobile node has registered
had to tunnel multicast packets to its current care-of address. While the
mobile node is away from home, the home agent intercepts
packets on in order to
transparently use its home address as the source of the multicast
packets. With Mobile IPv6, the use of the Home Address option
allows the home link destined address to be used but still be compatible with
multicast routing that is based in part on the mobile node's home packet's Source
Address.
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address, encapsulates them,
- There is no longer any need to deploy special routers as
"foreign agents" as are used in Mobile IPv4. In Mobile IPv6,
mobile nodes make use of the enhanced features of IPv6, such
as Neighbor Discovery [13] and tunnels them Address Autoconfiguration [22],
to operate in any location away from home without any special
support required from its local router.
- Unlike Mobile IPv4, Mobile IPv6 utilizes IPsec [8, 9, 10] for
all security requirements (sender authentication, data integrity
protection, and replay protection) for Binding Updates (which
serve the role of both registration and Route Optimization in
Mobile IPv4). Mobile IPv4 relies on its own security mechanisms
for these functions, based on statically configured "mobility
security associations".
- The movement detection mechanism in Mobile IPv6 provides
bidirectional confirmation of a mobile node's registered care-of address.
care-of address
An IP address associated ability to
communicate with a its default router in its current location
(packets that the router sends are reaching the mobile node, and
packets that the mobile node while visiting a
foreign link; sends are reaching the subnet prefix of this IP address is router).
This confirmation provides a foreign
subnet prefix. Among detection of the multiple care-of addresses "black hole"
situation that a
mobile node may have at a time (e.g., with different subnet
prefixes), exist in some wireless environments where the one registered with
link to the router does not work equally well in both directions,
such as when the mobile node's home agent
is called its "primary" care-of address.
binding
The association node has moved out of good wireless
transmission range from the home address of a router. The mobile node with may then
attempt to find a new router and begin using a new care-of
address for that mobile node, along with the remaining
lifetime of that association.
3.3. Specification Language
The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [3].
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4. Overview of Mobile IPv6
4.1. Basic Operation
A mobile node is always addressable by if its home address, whether it
is currently attached link to its home link or current router is away not working well.
In contrast, in Mobile IPv4, only the forward direction (packets
from home. While
a the router are reaching the mobile node node) is at home, confirmed,
allowing the black hole condition to persist.
- Most packets addressed sent to its a mobile node while away from home address in
Mobile IPv6 are
routed to it tunneled using conventional Internet routing mechanisms in the
same way as if the node were never mobile. Since the subnet prefix an IPv6 Routing header rather than
IP encapsulation, whereas Mobile IPv4 must use encapsulation
for all packets. The use of a mobile node's home address is the subnet prefix (or one of Routing header requires less
additional header bytes to be added to the
subnet prefixes) on packet, reducing the mobile node's home link (it is
overhead of Mobile IP packet delivery. To avoid modifying the
packet in flight, however, packets intercepted and tunneled
by a mobile node's home subnet prefix), packets addressed to it will be routed to
its home link. agent in Mobile IPv6 must still use
encapsulation for tunneling.
- While a mobile node is attached to some foreign link away from home, it is also addressable by one or more care-of addresses, in
addition to its home address. A care-of address is an IP address
associated with a agent intercepts
any packets for the mobile node while visiting a particular foreign
link. that arrive at the home network,
using IPv6 Neighbor Discovery [13] rather than ARP [18] as is
used in Mobile IPv4. The subnet prefix use of a mobile node's care-of address is Neighbor Discovery improves
the
subnet prefix (or one robustness of the subnet prefixes) on protocol (e.g., due to the foreign Neighbor
Advertisement "override" bit) and simplifies implementation
of Mobile IP due to the ability to not be concerned with any
particular link
being visited by layer as is required in ARP.
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- The use of IPv6 encapsulation (and the mobile node; if Routing header) removes
the mobile node is connected need in Mobile IPv6 to this foreign link while using that care-of address, packets
addressed manage "tunnel soft state", which was
required in Mobile IPv4 due to this care-of address will be routed limitations in ICMP for IPv4. Due
to the mobile node definition of ICMP for IPv6, the use of tunnel soft state
is no longer required in its location away IPv6 for correctly relaying ICMP error
messages from home. within the tunnel back to the original sender of
the packet.
- The association between a mobile
node's dynamic home agent address discovery mechanism in Mobile IPv6
uses IPv6 anycast and care-of address is known as returns a "binding"
for single reply to the mobile node. A mobile node typically acquires its care-of
address through stateless [18] or stateful (e.g., DHCPv6 [2])
address autoconfiguration, according to node,
rather than the methods of IPv6 Neighbor
Discovery [11]. Other methods of acquiring corresponding Mobile IPv4 mechanism that used
IPv4 directed broadcast and returned a care-of address
are also possible, but such methods are beyond the scope of this
document.
While away separate reply from home, each
home agent on the mobile node registers one of its bindings
with a router on its node's home link, requesting this router link. The Mobile IPv6
mechanism is more efficient and more reliable, since only
one packet need be sent back to function
as the "home agent" for the mobile node. This binding registration
is done by node and since the
mobile node sending a packet with a "Binding Update"
destination option is less likely to lose one of the home agent; the home agent then replies because no
"implosion" of replies is required by
returning a packet containing a "Binding Acknowledgement" destination the protocol.
- Mobile IPv6 defines an Advertisement Interval option on
Router Advertisements (equivalent to the mobile node. The care-of address Agent Advertisements in this binding
registered with its home agent is known as the mobile node's "primary
care-of address". The
Mobile IPv4), allowing a mobile node's home agent thereafter uses proxy
Neighbor Discovery node to intercept any decide for itself how
many Router Advertisements (Agent Advertisements) it is willing
to miss before declaring its current router unreachable.
- The use of IPv6 packets addressed destination options allows all Mobile IPv6
control traffic to the
mobile node's home address (or home addresses) be piggybacked on the home link, any existing IPv6 packets,
whereas in Mobile IPv4 and tunnels each intercepted packet to the mobile node's primary
care-of address. To tunnel its Route Optimization extensions,
separate UDP packets were required for each intercepted packet, the home agent
encapsulates the packet using IPv6 encapsulation [4], with the outer control message.
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3. Terminology
3.1. General Terms
IP
Internet Protocol Version 6 (IPv6).
node
A device that implements IP.
router
A node that forwards IP packets not explicitly addressed to
itself.
host
Any node that is not a router.
link
A communication facility or medium over which nodes can
communicate at the mobile node's primary care-of address.
Section 10.12 discusses link layer, such as an Ethernet (simple or
bridged). A link is the reasons why it may be desirable for layer immediately below IP.
interface
A node's attachment to a mobile node link.
subnet prefix
A bit string that consists of some number of initial bits of an
IP address.
interface identifier
A number used to use more than one care-of identify a node's interface on a link. The
interface identifier is the remaining low-order bits in the
node's IP address at after the same subnet prefix.
link-layer address
A link-layer identifier for an interface, such as IEEE 802
addresses on Ethernet links.
packet
An IP header plus payload.
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time. However, a mobile node's primary care-of address is distinct
among these in that the
3.2. Mobile IPv6 Terms
home agent maintains only a single care-of address registered for each mobile node, and always tunnels
An IP address assigned to a mobile
node's packets intercepted from node within its home link link.
home subnet prefix
The IP subnet prefix corresponding to this a mobile node's
registered primary care-of home
address. The
home agent thus need not
implement any policy to determine which of possibly many care-of
addresses to link
The link on which to tunnel each intercepted packet, leaving the a mobile node entirely in control of this policy by which of its
care-of addresses it registers with its node's home agent.
It subnet prefix is possible that while
defined. Standard IP routing mechanisms will deliver packets
destined for a mobile node's home address to its home link.
mobile node is away
A node that can change its point of attachment from home, some nodes
on one link to
another, while still being reachable via its home link may be reconfigured, address.
movement
A change in a mobile node's point of attachment to the Internet
such that it is no longer connected to the router that was
operating same link as the mobile node's home agent is replaced by it was
previously. If a different
router serving this role. In this case, the mobile node may is not
know the IP address of currently attached to its own home agent. Mobile IPv6 provides a
mechanism, known as "dynamic
home agent address discovery", that
allows a link, the mobile node is said to dynamically discover the IP address of a home
agent on its home link be "away from home".
correspondent node
A peer node with which it may register its care-of address
while away from home. The a mobile node sends a Binding Update to the
"Home-Agents anycast address" for its home is communicating. The
correspondent node may be either mobile or stationary.
foreign subnet prefix and thus
reaches one of
Any IP subnet prefix other than the (possibly many) routers on its mobile node's home subnet
prefix.
foreign link currently
operating as a
Any link other than the mobile node's home agent. This link.
home agent rejects the
A router on a mobile node's Binding Update, but returns in the Binding Acknowledgement
in response a list of all home agents on link with which the home link. This list
of home agents mobile
node has registered its current care-of address. While the
mobile node is maintained by each away from home, the home agent intercepts
packets on the home link
through use of destined to the Home Agent (H) bit in each mobile node's home agent's periodic
unsolicited multicast Router Advertisements.
The Binding Update
Johnson and Binding Acknowledgement destination options,
together with a "Binding Request" destination option, are also used
to allow Perkins Expires 4 February 1999 [Page 7]
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learn 4 August 1998
address, encapsulates them, and cache tunnels them to the mobile
node's binding. When sending a packet
to any IPv6 destination, registered care-of address.
care-of address
An IP address associated with a mobile node checks its cached bindings for an
entry for the packet's destination address. If while visiting a cached binding for
foreign link; the subnet prefix of this destination IP address is found, a foreign
subnet prefix. Among the multiple care-of addresses that a
mobile node uses an IPv6 Routing
header [5] (instead of IPv6 encapsulation) to route may have at a time (e.g., with different subnet
prefixes), the packet to one registered with the mobile node by way node's home agent
is called its "primary" care-of address.
binding
The association of the care-of home address indicated in this
binding. If, instead, the sending of a mobile node has no cached binding with a
care-of address for
this destination address, the node sends the packet normally (with
no Routing header), and that mobile node, along with the packet is subsequently intercepted remaining
lifetime of that association.
3.3. Specification Language
The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and
tunneled by the mobile node's home agent as described above. A node
communicating with a mobile node is referred to "OPTIONAL" in this
document as a
"correspondent node" of the mobile node.
Since a Binding Update, Binding Acknowledgement, and Binding Request are each represented in a packet as an IPv6 destination option [5],
they may be included in any IPv6 packet. Any of these options can to be
sent interpreted as described in either of two ways: RFC 2119 [3].
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- A Binding Update, Binding Acknowledgement, or Binding Request can
be included within any
4. Overview of Mobile IPv6 packet carrying any payload such as
TCP [16] or UDP [15].
-
4.1. Basic Operation
A Binding Update, Binding Acknowledgement, or Binding Request can
be sent as a separate IPv6 packet containing no payload. In this
case, the Next Header field in the last extension header in the
packet mobile node is set to the value 59, always addressable by its home address, whether it
is currently attached to indicate "No Next Header" [5].
Mobile IPv6 also defines one additional IPv6 destination option.
When its home link or is away from home. While
a mobile node sends a packet while away from is at home, it will
generally set the Source Address in the packet's IPv6 header packets addressed to one
of its current care-of addresses, and will also include a "Home
Address" destination option in the packet, giving the mobile node's home address. Many routers implement security policies such as
"ingress filtering" [6] that do not allow forwarding of packets
that appear to have a Source Address that is not topologically
correct. By using the care-of address as the IPv6 header Source
Address, the packet will be able to pass normally through such
routers, yet ingress filtering rules will still be able are
routed to locate
the true physical source of the packet it using conventional Internet routing mechanisms in the
same way as packets
from non-mobile nodes. By also including the Home Address option,
the sending mobile node can communicate its home address to if the
correspondent node receiving this packet, allowing the use of the
care-of address to be transparent above the Mobile IPv6 support
level (e.g., at were never mobile. Since the transport layer). The inclusion subnet prefix
of a Home
Address option in a packet affects only the correspondent mobile node's
receipt of this single packet; no state home address is created or modified in the
correspondent node as a result subnet prefix (or one of receiving a Home Address option in
a packet.
4.2. New IPv6 Destination Options
As discussed in general in Section 4.1, the following four new IPv6
destination options are defined for Mobile IPv6:
Binding Update
A Binding Update option is used by a mobile node to notify
a correspondent node or
subnet prefixes) on the mobile node's home agent of
its current binding. The Binding Update sent to link (it is the mobile
node's home agent subnet prefix), packets addressed to it will be routed to register
its primary care-of address is
marked as a "home registration". Any packet that includes home link.
While a
Binding Update option MUST also include either an AH [7] or
ESP [8] header providing sender authentication, data integrity
protection, and replay protection. The Binding Update option
is described in detail in Section 5.1.
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Binding Acknowledgement
A Binding Acknowledgement option mobile node is used attached to acknowledge receipt
of a Binding Update, if an acknowledgement was requested
in the Binding Update. Any packet that includes a Binding
Acknowledgement option MUST some foreign link away from home,
it is also include either an AH [7] addressable by one or
ESP [8] header providing sender authentication, data integrity
protection, and replay protection. The Binding Acknowledgement
option is described in detail more care-of addresses, in Section 5.2.
Binding Request addition
to its home address. A Binding Request option care-of address is used to request an IP address associated
with a mobile node
to send while visiting a particular foreign link. The
subnet prefix of a Binding Update to the requesting node, containing
the mobile node's current binding. This option care-of address is typically
used by a correspondent node to refresh a cached binding for
a mobile node, when the cached binding is in active use but subnet prefix
(or one of the binding's lifetime is close to expiration. No special
authentication is required for subnet prefixes) on the Binding Request option. The
Binding Request option is described in detail in Section 5.3.
Home Address
A Home Address option is used in a packet sent foreign link being visited by a mobile
node to inform
the recipient of that packet of mobile node; if the mobile
node's home address. For packets sent by a mobile node is connected to this foreign link
while
away from home, using that care-of address, packets addressed to this care-of
address will be routed to the mobile node generally uses one of its
care-of addresses as the Source Address in the packet's IPv6
header. By including its location away from
home.
The association between a Home Address option in the packet, the
correspondent node receiving the packet is able to substitute
the mobile node's home address for this and care-of
address when
processing the packet, thus making the use of is known as a "binding" for the mobile node. A mobile node
typically acquires its care-of address transparent through stateless [22] or
stateful (e.g., DHCPv6 [2]) address autoconfiguration, according
to the correspondent node. If the IP
header methods of IPv6 Neighbor Discovery [13]. Other methods
of acquiring a packet carrying a Home Address option is covered
by authentication, then the Home Address option MUST care-of address are also
be covered possible, such as static
pre-assignment by this authentication, but no other special
authentication is required for the Home Address option. The
Home Address option is described in detail in Section 5.4.
Extensions to the format owner or manager of these options MAY be included after the
fixed portion a particular foreign link,
but details of such other methods are beyond the option data specified in scope of this
document. The
presence
While away from home, a mobile node registers one of such extensions will be indicated by the Option Length
field within its care-of
addresses with a router on its home link, requesting this router
to function as the option. When "home agent" for the Option Length mobile node. This binding
registration is greater than done by the
length required for mobile node sending to the option specified here, home agent
a packet containing a "Binding Update" destination option; the remaining octets
are interpreted
home agent then replies to the mobile node by returning a packet
containing a "Binding Acknowledgement" destination option. The
care-of address in this binding registered with its home agent is
known as extensions. Currently, no extensions have been
defined. the mobile node's "primary care-of address". The mobile
node's home agent thereafter uses proxy Neighbor Discovery to
intercept any IPv6 packets addressed to the mobile node's home
address (or home addresses) on the home link, and tunnels each
intercepted packet to the mobile node's primary care-of address.
To tunnel each intercepted packet, the home agent encapsulates the
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4.3. Conceptual Data Structures
This document describes the Mobile IPv6 protocol in terms of the
following three conceptual data structures used in the maintenance of
cached bindings:
Binding Cache
A cache, maintained by each
packet using IPv6 node, of bindings for
other nodes. The Binding Cache MAY be implemented in any
manner consistent encapsulation [4], with the external behavior described
in this document, for example by being combined with outer IPv6 header
addressed to the mobile node's Destination Cache as maintained through Neighbor
Discovery [11]. When sending a packet, primary care-of address.
Section 10.15 discusses the Binding Cache
MUST reasons why it may be searched before the Neighbor Discovery conceptual
Destination Cache [11]. Each Binding Cache entry conceptually
contains the following fields:
- The home address of the desirable for
a mobile node for which this is the
Binding Cache entry. This field is used as the key for
searching the Binding Cache for the destination to use more than one care-of address of
a packet being routed. If at the destination same
time. However, a mobile node's primary care-of address of the
packet matches is distinct
among these in that the home agent maintains only a single care-of
address in the Binding Cache entry, registered for each mobile node, and always tunnels a mobile
node's packets intercepted from its home link to this entry SHOULD be used in routing that packet.
- mobile node's
registered primary care-of address. The home agent thus need not
implement any policy to determine which of possibly many care-of address for
addresses to which to tunnel each intercepted packet, leaving the
mobile node indicated by
the home address field entirely in this Binding Cache entry. If
the destination address control of a packet being routed this policy by which of its
care-of addresses it registers with its home agent.
It is possible that while a mobile node matches the is away from home, some nodes
on its home address in this entry, the packet
SHOULD link may be routed to this care-of address, reconfigured, such that the router that was
operating as described in
Section 8.9, for packets originated by this node, or in
Section 9.5, if this node is the mobile node's home agent
and the packet was intercepted is replaced by it on the home link.
- A lifetime value, indicating the remaining lifetime
for a different
router serving this Binding Cache entry. The lifetime value is
initialized from the Lifetime field in the Binding Update
that created or last modified role. In this Binding Cache entry.
Once case, the lifetime on this entry expires, the entry MUST be
deleted from the Binding Cache.
- A flag indicating whether or mobile node may not this Binding Cache entry
is a "home registration" entry.
- The value of the Prefix Length field received in
know the
Binding Update that created or last modified this Binding
Cache entry.
- The maximum value IP address of the Sequence Number field received in
previous Binding Updates for this mobile node its own home address.
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All comparisons between Sequence Number values MUST be
performed modulo 2**16.
- Recent usage information for this Binding Cache entry, provides a
mechanism, known as needed for the cache replacement policy in use in the
Binding Cache and to assist in determining whether "dynamic home agent address discovery", that
allows a
Binding Request should be sent when mobile node to dynamically discover the lifetime IP address of a home
agent on this
entry nears expiration.
- The time at its home link with which it may register its care-of address
while away from home. The mobile node sends a Binding Request was last sent for this
entry, as needed Update to implement the rate limiting restriction
for sending Binding Requests.
An entry in a node's Binding Cache
"Home-Agents anycast address" for which its own home subnet prefix and thus
reaches one of the node is
serving as a (possibly many) routers on its home agent is marked link currently
operating as a "home registration"
entry and SHOULD NOT be deleted by the home agent. This home agent until rejects the
expiration of its binding lifetime. Other Binding Cache
entries MAY be replaced at any time by any reasonable local
cache replacement policy but SHOULD NOT be unnecessarily
deleted. Any node's Binding Cache may contain at most one
entry for each mobile node home address. The contents of a
node's Binding Cache MUST NOT be changed Update, but returns in response to a Home
Address option the Binding Acknowledgement
in response a received packet.
Binding Update List
A list, list of all home agents on the home link. This list
of home agents is maintained by each mobile node, recording information
for each Binding Update sent by this mobile node, for which home agent on the Lifetime sent home link
through use of the Home Agent (H) bit in that Binding Update has not yet expired. each home agent's periodic
unsolicited multicast Router Advertisements.
The Binding Update List includes all bindings sent by the
mobile node: those and Binding Acknowledgement destination options,
together with a "Binding Request" destination option, are also used
to correspondent nodes, allow IPv6 nodes communicating with a mobile node, to dynamically
learn and cache the mobile node's home agent, and to binding. When sending a previous default router of the
mobile node. The Binding Update List MAY be implemented in packet
to any
manner consistent with the external behavior described in this
document. Each Binding Update List IPv6 destination, a node checks its cached bindings for an
entry conceptually contains for the following fields:
- The IP packet's destination address. If a cached binding for
this destination address of is found, the node uses an IPv6 Routing
header [5] (instead of IPv6 encapsulation) to which a Binding Update was
sent. This node might still have a Binding Cache entry
derived from this Binding Update, if route the Binding Update was
successfully received by that packet to
the mobile node (e.g., not lost by way of the
network) and if that care-of address indicated in this
binding. If, instead, the sending node has not deleted the entry before
its expiration (e.g., to reclaim space in its Binding Cache
for other entries).
- The home address no cached binding for which that Binding Update was sent.
This will be
this destination address, the node sends the packet normally (with
no Routing header), and the packet is subsequently intercepted and
tunneled by the mobile node's home address for most
Binding Updates (Sections 10.4 agent as described above. Any
node communicating with a mobile node is referred to in this document
as a "correspondent node" of the mobile node, and 10.5), but will may itself be
the
either a stationary node or a mobile node's previous care-of address for Binding node.
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Updates sent to the mobile node's previous default router
(Section 10.6).
- The care-of address sent in that Binding Update. This
value is necessary for determining if the mobile node has
sent
Since a Binding Update giving its new care-of address to
this Update, Binding Acknowledgement, and Binding Request
are each represented in a packet as an IPv6 destination after changing its care-of address.
- The remaining lifetime option [5],
they may be included in any IPv6 packet. Any of that binding. This lifetime is
initialized from the Lifetime value these options can be
sent in the Binding
Update and is decremented until it reaches zero, at which
time this entry MUST be deleted from the Binding Update
List.
- The maximum value either of the Sequence Number field sent
in previous Binding Updates to this destination. All
comparisons between Sequence Number values MUST be
performed modulo 2**16. two ways:
- The state of any retransmissions needed for this A Binding Update, if the Acknowledge (A) bit was set in this Binding
Update. This state includes the time remaining until the
next retransmission attempt for the Binding Update, and
the current state of the exponential back-off process for
retransmissions.
- The time at which a Acknowledgement, or Binding Update was last sent to this
destination, Request can
be included within any IPv6 packet carrying any payload such as needed to implement the rate limiting
restriction for sending Binding Updates.
TCP [20] or UDP [19].
- A flag that, when set, indicates that future Binding
Updates should not Update, Binding Acknowledgement, or Binding Request can
be sent to this destination. The
mobile node sets as a separate IPv6 packet containing no payload. In this flag
case, the Next Header field in the Binding Update List
entry when it receives an ICMP Parameter Problem, Code 2,
error message last extension header in response to a Binding Update sent the
packet is set to that
destination, as described in Section 10.9.
Home Agents List
A list, maintained by each home agent, recording the IP address
of each other home agent on value 59, to indicate "No Next Header" [5].
Mobile IPv6 also defines one additional IPv6 destination option.
When a link on which this mobile node is
serving as sends a home agent; packet while away from home, it will
generally set the home agent maintains Source Address in the packet's IPv6 header to one
of its current care-of addresses, and will also include a separate
Home Agents List for each such link on which it is serving.
This list is used "Home
Address" destination option in the dynamic packet, giving the mobile node's
home agent address. Many routers implement security policies such as
"ingress filtering" [6] that do not allow forwarding of packets that
appear to have a Source Address that is not topologically correct.
By using the care-of address discovery
mechanism. The information for as the list is learned IPv6 header Source Address,
the packet will be able to pass normally through
receipt such routers,
yet ingress filtering rules will still be able to locate the true
topological source of periodic unsolicited multicast Router Advertisements
from each other home agent on the link, packet in which the Home
Agent (H) bit is set, in a manner similar to same way as packets from
non-mobile nodes. By also including the Default
Router List conceptual data structure maintained by each host
for Neighbor Discovery [11]. The Home Agents List MAY be
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implemented in any manner consistent with the external behavior
described Address option in this document. Each Home Agents List entry
conceptually contains each
packet, the following fields:
- The IP sending mobile node can communicate its home address of another router on to
the home link that this correspondent node currently believes is operating as a home agent for receiving this link. A new entry is created or an existing entry is
updated in packet, allowing the Home Agents List in response use of
the care-of address to receipt be transparent above the Mobile IPv6 support
level (e.g., at the transport layer). The inclusion of a
valid Router Advertisement Home
Address option in which a packet affects only the Home Agent (H) bit
is set.
- The remaining lifetime correspondent node's
receipt of this Home Agents List entry. The
lifetime single packet; no state is initialized from the Router Lifetime field created or modified in the received Router Advertisement and is decremented until
it reaches zero, at which time this entry MUST be deleted
from the
correspondent node as a result of receiving a Home Agents List.
4.4. Address option in
a packet.
4.2. New IPv6 Destination Options
As discussed in general in Section 4.1, the following four new IPv6
destination options are defined for Mobile IPv6:
Binding Management
When Update
A Binding Update option is used by a mobile node configures a new care-of address and decides to
use this new address as its primary care-of address, the mobile notify
a correspondent node registers this new binding with its home agent by sending or the mobile node's home agent a Binding Update. of
its current binding. The mobile node indicates
that an acknowledgement is needed for this Binding Update and
continues sent to periodically retransmit it until acknowledged. The the mobile
node's home agent acknowledges the Binding Update by returning a Binding
Acknowledgement to the mobile node.
When a mobile node receives register its primary care-of address is
marked as a "home registration". Any packet tunneled to it from its
home agent, the mobile node assumes that the original sending
correspondent node has no includes a
Binding Cache entry for the mobile node,
since the correspondent node would otherwise have sent the packet
directly Update option MUST also include either an AH [8] or
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ESP [9] header providing sender authentication, data integrity
protection, and replay protection. The Binding Update option
is described in detail in Section 5.1.
Binding Acknowledgement
A Binding Acknowledgement option is used to acknowledge receipt
of a Binding Update, if an acknowledgement was requested
in the mobile node using Binding Update. Any packet that includes a Routing header. Binding
Acknowledgement option MUST also include either an AH [8] or
ESP [9] header providing sender authentication, data integrity
protection, and replay protection. The Binding Acknowledgement
option is described in detail in Section 5.2.
Binding Request
A Binding Request option is used to request a mobile node
thus returns a Binding Update to the correspondent node, allowing
it
send to cache the mobile node's binding for routing future packets.
Although the mobile requesting node may request an acknowledgement for this a Binding Update, it need not, since subsequent packets from the
correspondent node will continue to be intercepted and tunneled by Update containing the
mobile node's home agent, effectively causing any needed Binding
Update retransmission.
A current binding. This option is typically used
by a correspondent node with to refresh a Binding Cache entry cached binding for a
mobile node
may refresh this binding, for example if node, when the cached binding is in active use but the
binding's lifetime is near expiration, by sending a Binding Request close to the mobile
node. Normally, a correspondent node will only refresh a expiration. No authentication
is required for the Binding
Cache entry Request option. The Binding
Request option is described in this way if it detail in Section 5.3.
Home Address
A Home Address option is actively communicating with the used in a packet sent by a mobile
node and has indications, such as an open TCP connection to inform the mobile node, recipient of that it will continue this communication in packet of the
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future. When a mobile node receives a Binding Request, it replies
node's home address. For packets sent by
returning a Binding Update to the mobile node sending while
away from home, the Binding Request.
A mobile node may use more than one care-of address at the same
time, although only generally uses one care-of address may be registered for it at
its home agent as of its primary
care-of address. The mobile node's
home agent will tunnel all intercepted packets for addresses as the mobile Source Address in the packet's IPv6
header. By including a Home Address option in the packet, the
correspondent node receiving the packet is able to its (single) registered primary care-of address, but substitute
the mobile
node will accept packets that it receives at any of its current node's home address for this care-of addresses. Use address when
processing the packet, thus making the use of more than one the care-of
address by a mobile
node may be useful, for example, transparent to improve smooth handoff when the
mobile node moves from one wireless link to another. correspondent node. If each the IP
header of
these wireless links is connected to the Internet through a separate
base station, such that the wireless transmission range from the
two base stations overlap, packet carrying a Home Address option is covered
by authentication, then the mobile node may Home Address option MUST also be able to remain
connected to both links while
covered by this authentication, but no other authentication is
required for the Home Address option. The Home Address option
is described in detail in Section 5.4.
Extensions to the area format of overlap. In this case,
the mobile node could acquire a new care-of address on these options MAY be included after the new link
before moving out
fixed portion of transmission range and disconnecting from the
old link. option data specified in this document. The mobile node may thus still accept packets at its
old care-of address while it works to update its home agent and
correspondent nodes, notifying them
presence of its new care-of address on the
new link.
Since correspondent nodes cache bindings, it is expected that
correspondent nodes usually such extensions will route packets directly to be indicated by the mobile
node's care-of address, so that Option Length
field within the home agent is rarely involved
with packet transmission to option. When the mobile node. This Option Length is essential for
scalability and reliability, and for minimizing overall network load.
By caching the care-of address of a mobile node, optimal routing of
packets can be achieved from the correspondent node to greater than the mobile
node. Routing packets directly to
length required for the mobile node's care-of address
also eliminates congestion at option specified here, the mobile node's home agent and home
link. In addition, the impact of any possible failure of the home
agent, the home link, or intervening networks leading to or from the
home link is reduced, since these nodes and links remaining octets
are not involved in
the delivery of most packets to the mobile node. interpreted as extensions. Currently, no extensions have been
defined.
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5. New
4.3. Conceptual Data Structures
This document describes the Mobile IPv6 Destination Options
5.1. protocol in terms of the
following three conceptual data structures:
Binding Update Option Format Cache
A cache, maintained by each IPv6 node, of bindings for other
nodes. The Binding Update destination option is used Cache MAY be implemented in any manner
consistent with the external behavior described in this
document, for example by being combined with the node's
Destination Cache as maintained by Neighbor Discovery [13].
When sending a packet, the Binding Cache is searched before the
Neighbor Discovery conceptual Destination Cache [13] (i.e., any
Binding Cache entry for this destination SHOULD take precedence
over any Destination Cache entry for the same destination).
Each Binding Cache entry conceptually contains the following
fields:
- The home address of the mobile node to
notify other nodes for which this is the
Binding Cache entry. This field is used as the key for
searching the Binding Cache for the destination address of
a new care-of address.
The packet being sent. If the destination address of the
packet matches the home address in the Binding Update option is encoded Cache entry,
this entry SHOULD be used in type-length-value (TLV)
format as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Type | Option Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|A|H|C| Reserved| Prefix Length | Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Care-of Address +
| (only present if C bit set) |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Option Type
195 ???
Option Length
8-bit unsigned integer. Length of routing that packet.
- The care-of address for the option, in octets,
excluding mobile node indicated by
the Option Type and Option Length fields. For home address field in this Binding Cache entry. If
the
current definition destination address of a packet being routed by a
node matches the Binding Update option, home address in this entry, the minimum
value packet
SHOULD be routed to this care-of address, as described in
Section 8.9, for packets originated by this field node, or in
Section 9.6, if this node is 8; the length is 24 if mobile node's home agent
and the Care-of
Address Present (C) bit is set.
Acknowledge (A)
The Acknowledge (A) bit is set packet was intercepted by it on the sending node to request a
Binding Acknowledgement (Section 5.2) be returned upon receipt
of home link.
- A lifetime value, indicating the remaining lifetime
for this Binding Update option.
Home Registration (H) Cache entry. The Home Registration (H) bit lifetime value is set by
initialized from the sending mobile node
to request Lifetime field in the receiving node to act as Binding Update
that created or last modified this node's home agent. Binding Cache entry.
Once the lifetime on this entry expires, the entry MUST be
deleted from the Binding Cache.
- A flag indicating whether or not this Binding Cache entry
is a "home registration" entry.
- The value of the Prefix Length field received in the
Binding Update that created or last modified this Binding
Cache entry. This field is only valid if the "home
registration" flag is set on this Binding Cache entry.
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- The Destination Address in the IP header maximum value of the packet carrying Sequence Number field received
in previous Binding Updates for this option mobile node home
address. The Sequence Number field is 16 bits long, and
all comparisons between Sequence Number values MUST be that of a router sharing the same subnet
prefix
performed modulo 2**16.
- Recent usage information for this Binding Cache entry, as
needed to implement the home address of the mobile node cache replacement policy in the binding
(given by the Home Address field use in
the Home Address option Binding Cache and to assist in determining whether a
Binding Request should be sent when the packet).
Care-of Address Present (C) lifetime on this
entry nears expiration.
- The Care-of Address Present (C) bit indicates the presence of
the Care-of Address field in the time at which a Binding Update. The care-of
address Request was last sent for this binding is either
entry, as needed to implement the address rate limiting restriction
for sending Binding Requests.
An entry in a node's Binding Cache for which the Care-of
Address field in the Binding Update, if this bit is set, or the
Source Address in the packet's IPv6 header, if this bit node is not
set.
Reserved
Sent
serving as 0; ignored on reception.
Prefix Length
The Prefix Length field a home agent is valid only for marked as a "home registration"
Binding Update. This field MUST
entry and SHOULD NOT be zero if deleted by the Home
Registration (H) bit is not set in home agent until the
expiration of its binding lifetime. Other Binding Update. The
Prefix Length field is set Cache
entries MAY be replaced at any time by the sending any reasonable local
cache replacement policy but SHOULD NOT be unnecessarily
deleted. Any node's Binding Cache may contain at most one
entry for each mobile node to the
(nonzero) length of its subnet prefix in its home address
(given address. The contents of a
node's Binding Cache MUST NOT be changed in the response to a Home
Address option in a received packet.
Binding Update List
A list, maintained by each mobile node, recording information
for each Binding Update sent by this mobile node, for which
the packet) Lifetime sent in that Binding Update has not yet expired.
The Binding Update List includes all bindings sent by the
mobile node: those to request
its home agent correspondent nodes, to use the interface identifier in the mobile
node's home address (the remaining low-order bits after the
indicated subnet prefix) agent, and to form all other appropriate home
addresses for a previous default router of the
mobile node. The home agent becomes the
home agent not only for the individual home address given Binding Update List MAY be implemented in
this binding, but also for all other home addresses for this
mobile node formed from this interface identifier. That is,
for each on-link prefix on the home link, the home agent uses
the interface identifier to form other valid addresses for the
mobile node on the home link, and acts as a home agent also
for those addresses. In addition, any
manner consistent with the home agent forms external behavior described in this
document. Each Binding Update List entry conceptually contains
the
link-local address and site-local following fields:
- The IP address corresponding to
this interface identifier, and defends each for purposes of
Duplicate Address Detection. Details of this operation are
described in Section 9.3.
Sequence Number
Used by the receiving node to sequence which a Binding Updates and by
the sending Update was
sent. This node to match might still have a returned Binding Acknowledgement
with Cache entry
created or updated from this Binding Update. Each Update, if the Binding
Update sent was successfully received by a mobile that node MUST use a Sequence Number greater than (e.g., not
lost by the Sequence
Number value sent in network) and if that node has not deleted the previous
entry before its expiration (e.g., to reclaim space in its
Binding Cache for other entries).
- The home address for which that Binding Update (if any) to was sent.
This will be one of the mobile node's home addresses for
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most Binding Updates (Sections 10.5 and 10.7), but will
be the same destination mobile node's previous care-of address (modulo 2**16). There is no
requirement, however, that the Sequence Number value strictly
increase by 1 with each new for Binding Update
Updates sent or received.
Lifetime
32-bit unsigned integer. The number of seconds remaining
before to the binding must be considered expired. A value of all
one bits (0xffffffff) indicates infinity. A value of zero
indicates mobile node's previous default router
(Section 10.8).
- The care-of address sent in that the Binding Cache entry Update. This
value is necessary for the mobile node
should be deleted.
Care-of Address to determine if it
has sent a Binding Update giving its new care-of address to
this destination after changing its care-of address.
- The remaining lifetime of that binding. This field lifetime is
initialized from the Lifetime value sent in the Binding
Update is optional and is only
present when the Care-of Address Present (C) bit is set. If
present, decremented until it gives reaches zero, at which
time this entry MUST be deleted from the care-of address Binding Update
List.
- The maximum value of the mobile node for
this binding. For most Sequence Number field sent in
previous Binding Updates sent, it is expected
that to this destination. The Sequence
Number field will not be present, is 16 bits long, and instead that the
care-of address for the binding will all comparisons between
Sequence Number values MUST be given by the Source
Address field in the packet's IPv6 header.
Any packet including performed modulo 2**16.
- The time at which a Binding Update option MUST also include a Home
Address option. was last sent to this
destination, as needed to implement the rate limiting
restriction for sending Binding Updates.
- The home address state of any retransmissions needed for this Binding
Update, if the mobile node in the binding
given Acknowledge (A) bit was set in the this Binding Update option is indicated by the Home Address
field in the Home Address option in the packet.
Any packet that
Update. This state includes a Binding Update option MUST also include
either an AH [7] or ESP [8] header providing sender authentication,
data integrity protection, and replay protection.
If the care-of address in the binding (either time remaining until the Care-of Address
field in
next retransmission attempt for the Binding Update option or the Source Address field in
the packet's IPv6 header) is equal to Update, and the home address
current state of the mobile
node, the Binding Update option indicates that any existing binding exponential back-off mechanism for the mobile node should be deleted. Likewise, if the Lifetime
field in the Binding Update option is equal to 0, the Binding Update
option
retransmissions.
- A flag that, when set, indicates that any existing binding for the mobile node should
be deleted. In each of these cases, no future Binding Cache entry for the
mobile node
Updates should not be created in response to receiving the Binding
Update.
The last Sequence Number value sent to a destination is stored by the this destination. The
mobile node sets this flag in the Binding Update List
entry for when it receives an ICMP Parameter Problem, Code 2,
error message in response to a Binding Update sent to that destination;
the last Sequence Number value received from
destination, as described in Section 10.13.
Home Agents List
A list, maintained by each home agent, recording information
about each other home agent on a mobile link on which this node
is stored
by serving as a correspondent node in the Binding Cache entry for that mobile
node. Thus, the mobile node's and the correspondent node's knowledge
of home agent; each home agent maintains a
separate Home Agents List for each such link on which it is
serving. This list is used in the last sequence number expire at dynamic home agent address
discovery mechanism. The information for the same time. If list is learned
through receipt of the sending
mobile node has no Binding Update List entry, periodic unsolicited multicast Router
Advertisements from each other home agent on the Sequence Number
may start at any value; if link, in which
the Home Agent (H) bit is set, in a manner similar to the receiving correspondent node has no
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Binding Cache entry, it should accept a Binding Update with any
Sequence Number value.
Default Router List conceptual data structure maintained by
each host for Neighbor Discovery [13]. The three highest-order bits of Home Agents List
MAY be implemented in any manner consistent with the Option Type are encoded to
indicate specific processing of external
behavior described in this document. Each Home Agents List
entry conceptually contains the option [5]. For following fields:
- The IP address of another router on the Binding
Update option, these three bits are set to 110, indicating home link that any
IPv6 node processing this option that does not recognize the Option
Type must discard the packet and, only if the packet's Destination
Address was not
node currently believes is operating as a multicast address, return home agent for
this link. A new entry is created or an ICMP Parameter
Problem, Code 2, message to existing entry is
updated in the packet's Source Address; and that the
data within the option cannot change en-route to the packet's final
destination.
Extensions Home Agents List in response to the Binding Update option format may be included after
the fixed portion receipt of a
valid Router Advertisement in which the Binding Update option specified above. Home Agent (H) bit
is set.
- The presence remaining lifetime of such extensions will be indicated by the Option
Length field. When the this Home Agents List entry. If
a Home Agent Information Option Length is greater than the length
defined above, the remaining octets are interpreted as extensions.
Currently, no extensions have been defined.
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5.2. Binding Acknowledgement Option Format
The Binding Acknowledgement destination option is used to acknowledge
receipt of a Binding Update option (Section 5.1). When a node
receives a packet containing Router
Advertisement received from a Binding Update option, with this node
being home agent, the destination node lifetime of
the packet (only the destination node
processes the option since it is a destination option), Home Agents List entry representing this node
MUST return a Binding Acknowledgement to home agent
is initialized from the source of Home Agent Lifetime field in the packet, if
option; otherwise, the Acknowledge (A) bit lifetime is set initialized from the
Router Lifetime field in the Binding Update. received Router Advertisement.
The Binding Acknowledgement option Home Agents List entry lifetime is encoded decremented until it
reaches zero, at which time this entry MUST be deleted from
the Home Agents List.
- The preference for this home agent, for use in type-length-value
(TLV) format as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+
| Option Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Length | Status | Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Refresh |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
. .
. Other ordering the
Home Agents .
. .
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Option Type
2 ???
Option Length
8-bit unsigned integer. Length of the option, List returned in octets,
excluding a Binding Acknowledgement;
higher values indicate a more preferable home agent. The
preference value is taken from the Option Type and Option Length fields. This Home Agent Preference
field
MUST be set to 11 + 16 * (the number of IP addresses included (a signed, twos-complement integer) in the Other Home Agents field). The number of addresses
included in received
Router Advertisement, if the Other Router Advertisement contains
a Home Agents field MUST be zero (Option
Length then MUST be set to 11), unless the Status field Agent Information Option, and is otherwise set to 135 (dynamic home agent
the default value of 0.
4.4. Binding Management
When a mobile node configures a new care-of address discovery response).
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Status
8-bit unsigned integer indicating decides to
use this new address as its primary care-of address, the disposition of mobile
node registers this new binding with its home agent by sending
the home agent a Binding Update. Values of the Status field less than 128
indicate The mobile node indicates
that the Binding Update was accepted by the receiving
node. The following such Status values are currently defined:
0 an acknowledgement is needed for this Binding Update accepted
Values of the Status field greater than or equal and
continues to 128
indicate that the Binding Update was rejected by the receiving
node. periodically retransmit it until acknowledged. The following such Status values are currently defined:
128 Reason unspecified
129 Poorly formed Binding Update
130 Administratively prohibited
131 Insufficient resources
132 Home registration not supported
133 Not home subnet
134 Sequence Number field value too small
135 Dynamic
home agent address discovery response
136 Incorrect interface identifier length
Up-to-date values of the Status field are to be specified in
the most recent "Assigned Numbers" [17].
Sequence Number
The Sequence Number in the Binding Acknowledgement is copied
from the Sequence Number field in acknowledges the Binding Update option,
for use by the mobile node in matching this Acknowledgement
with an outstanding returning a Binding Update.
Lifetime
The granted lifetime for which this node will attempt
Acknowledgement to retain the entry for this mobile node.
When a mobile node in receives a packet tunneled to it from its Binding Cache. If
home agent, the mobile node sending assumes that the original sending
correspondent node has no Binding Acknowledgement is serving as Cache entry for the mobile node's home agent, the Lifetime period also indicates node,
since the period for which this correspondent node will continue this service; if would otherwise have sent the mobile node requires home agent service from this node
beyond this period, packet
directly to the mobile node MUST send using a new Binding
Update to it before the expiration of this period, in order
to extend the lifetime. Routing header. The value of this field is undefined
if the Status field indicates that the Binding Update was
rejected. mobile node
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Refresh
The recommended period at which the mobile node SHOULD send
thus returns a new Binding Update to this node in order the correspondent node, allowing
it to "refresh" cache the mobile node's binding in for routing future packets to
it. Although the mobile node may request an acknowledgement for
this node's Binding Cache. This
refreshing of the binding is useful in case Update, it need not, since subsequent packets from the
correspondent node fails will continue to be intercepted and
loses its cache state. The Refresh period is determined tunneled by
the node sending the Binding Acknowledgement (the node caching
the binding). If this node is serving as the mobile node's home agent, the Refresh value effectively causing any needed Binding
Update retransmission.
A correspondent node with a Binding Cache entry for a mobile node
may be set, refresh this binding, for example, based on
whether example if the node stores binding's lifetime
is near expiration, by sending a Binding Request to the mobile node's binding in volatile
storage or in nonvolatile storage. If the
node. Normally, a correspondent node sending the will only refresh a Binding Acknowledgement
Cache entry in this way if it is not serving as actively communicating with the
mobile node's
home agent, the Refresh period SHOULD be set equal to the
Lifetime period in the Binding Acknowledgement; even if this node loses this cache entry due and has indications, such as an open TCP connection to a failure of
the mobile node,
packets from that it can still reach the mobile node through will continue this communication in the
future. When a mobile node's home agent, causing node receives a new Binding Update to this
node to allow Request, it replies by
returning a Binding Update to recreate this cache entry. The value of
this field is undefined if the Status field indicates that node sending the Binding Update was rejected.
Other Home Agents Request.
A list of other home agents on mobile node may use more than one care-of address at the same
time, although only one care-of address may be registered for it at
its home link agent as its primary care-of address. The mobile node's
home agent will tunnel all intercepted packets for the mobile node
to which this Binding Acknowledgement is sent. This field
MUST NOT be present (zero addresses listed) unless its (single) registered primary care-of address, but the Binding
Acknowledgement is sent in response to an anycast Binding
Update sent by this mobile
node attempting dynamic home agent will accept packets that it receives at any of its current
care-of addresses. Use of more than one care-of address discovery. In this case, the Status field MUST by a mobile
node may be
set useful, for example, to 135 (dynamic home agent address discovery response).
The list of home agents in improve smooth handoff when the Other Home Agents field MUST
NOT include this home agent's own unicast IP address, which
mobile node moves from one wireless link to another. If each of
these wireless links is returned instead connected to the Internet through a separate
base station, such that the wireless transmission range from the
two base stations overlap, the mobile node may be able to remain
connected to both links while in the Source Address
field in the IPv6 header area of the packet in which overlap. In this Binding
Acknowledgement is sent.
Any packet that includes a Binding Acknowledgement option MUST
also include either an AH [7] or ESP [8] header providing sender
authentication, data integrity protection, and replay protection.
If case,
the mobile node returning the Binding Acknowledgement accepted the
Binding Update for which could acquire a new care-of address on the Acknowledgement is being returned (the
value new link
before moving out of transmission range and disconnecting from the Status field in the Acknowledgement is less than 128),
this node will have an entry for the
old link. The mobile node in may thus still accept packets at its Binding Cache
old care-of address while it works to update its home agent and MUST use this entry (which includes the
correspondent nodes, notifying them of its new care-of address received
in the Binding Update) in sending the packet containing on the Binding
Acknowledgement
new link.
Since correspondent nodes cache bindings, it is expected that
correspondent nodes usually will route packets directly to the mobile node. The details of sending this
node's care-of address, so that the home agent is rarely involved
with packet transmission to the mobile node are the same as node. This is essential for sending any packet to a
mobile node using a binding,
scalability and are described in Section 8.9. The
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packet is sent using for minimizing overall network load.
By caching the care-of address of a Routing header, mobile node, optimal routing of
packets can be achieved from the packet correspondent node to the mobile node by way of its
node. Routing packets directly to the mobile node's care-of address recorded in the Binding
Cache entry.
If the node returning
also eliminates congestion at the Binding Acknowledgement instead
rejected mobile node's home agent and home
link. In addition, the Binding Update (the value impact of any possible failure of the Status field in home
agent, the
Acknowledgement is greater than home link, or equal intervening networks leading to 128), this node MUST
similarly use a Routing header in sending the packet containing or from the
Binding Acknowledgement, as described
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use its Binding Cache IPv6 4 August 1998
home link is reduced, since these nodes and links are not involved in forming
the IP header or Routing header
in this packet. Rather, delivery of most packets to the care-of address mobile node.
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5. New IPv6 Destination Options
5.1. Binding Update Option Format
The Binding Update destination option is used by this a mobile node in
sending the packet containing the Binding Acknowledgement MUST be
copied from the
to notify other nodes of a new care-of address received in the rejected Binding
Update; this node MUST NOT modify its Binding Cache for itself. As a
destination option, it MAY be included in response any existing packet being
sent to receiving this rejected Binding Update and MUST ignore its
Binding Cache same destination or MAY be sent in sending the a packet in which it returns this Binding
Acknowledgement. The by itself;
a packet containing a Binding Update is sent using a Routing header, routing
the packet to the home address of the rejected Binding Update by
way of the care-of address indicated in the same way as any
packet containing the
Binding Update. When sending a Binding Acknowledgement to reject a
Binding Update, the Binding Acknowledgement MUST be sent in an IPv6
packet containing no payload (with the Next Header field in the last
extension header in the packet set to indicate "No Next Header" [5]).
The three highest-order bits of the Option Type are encoded to
indicate specific processing of the option [5]. For the Binding
Acknowledgement option, these three bits are set to 000, indicating
that any IPv6 node processing this option that does not recognize the
Option Type must skip over this option and continue processing the
header, and that the data within the option cannot change en-route to
the packet's final destination.
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5.3. Binding Request Option Format
The Binding Request destination option is used to request a mobile
node's binding from the mobile node. When by a mobile node receives
a packet containing a Binding Request option, it SHOULD return a
Binding Update (Section 5.1) to the source of the Binding Request. 10.1).
The Binding Request Update option is encoded in type-length-value (TLV)
format as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Type | Option Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Option Type
3 ???
Option Length
8-bit unsigned integer. Length of the option, in octets,
excluding the Option Type and Option
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|A|H|C| Reserved| Prefix Length fields. For the
current definition of | Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Care-of Address +
| (only present if C bit set) |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Option Type
195 ???
Option Length
8-bit unsigned integer. Length of the Binding Request option, this field
MUST be set to 0.
The three highest-order bits of in octets,
excluding the Option Type are encoded to
indicate specific processing of the option [5]. and Option Length fields. For the
current definition of the Binding
Request Update option, these three bits are set to 000, indicating that any
IPv6 node processing this option that does not recognize the Option
Type must skip over minimum
value for this option and continue processing the header,
and that field is 8; the data within length is 24 if the option cannot change en-route to Care-of
Address Present (C) bit is set.
Acknowledge (A)
The Acknowledge (A) bit is set by the
packet's final destination.
Extensions sending mobile node to the
request a Binding Request option format may Acknowledgement (Section 5.2) be included after
the fixed portion returned
upon receipt of the Binding Request option specified above.
The presence of such extensions will be indicated by the Option
Length field. When the Option Length is greater than 0 octets,
the remaining octets are interpreted as extensions. Currently, no
extensions have been defined. Update.
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5.4.
Home Address Option Format Registration (H)
The Home Address destination option Registration (H) bit is used in a packet sent set by a the sending mobile node
to inform the recipient of that packet of request the mobile receiving node to act as this node's home address. For packets sent by a mobile node while
away from home, the mobile node generally uses one agent.
The destination of its care-of
addresses as the Source Address in the packet's IPv6 header. By
including a Home Address packet carrying this option in the packet, the correspondent
node receiving MUST be that
of a router sharing the packet is able to substitute same subnet prefix as the mobile node's home address for this care-of address when processing the packet,
thus making the use
of the care-of address transparent to mobile node in the binding (given by the
correspondent node.
The Home Address option is encoded
field in type-length-value (TLV) format
as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Type | Option Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ the Home Address +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Option Type
196 ???
Option Length
8-bit unsigned integer. Length of the option, option in octets,
excluding the Option Type and Option Length fields. For packet).
Care-of Address Present (C)
The Care-of Address Present (C) bit indicates the
current definition presence of
the Home Care-of Address option, this field MUST
be set to 16.
Home Address in the Binding Update. The home care-of
address of for this binding is either the mobile node sending address in the packet.
The inclusion of a Home Care-of
Address option field in a packet affects only the correspondent node's receipt of Binding Update, if this single packet; no state bit is created set, or modified in the correspondent node as a result of
receiving a Home
Source Address option in a packet. In particular, the
receipt of a packet containing a Home Address option MUST NOT alter
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the contents of the receiver's header, if this bit is not
set.
Reserved
Sent as 0; ignored on reception.
Prefix Length
The Prefix Length field is valid only for a "home registration"
Binding Cache due to the presence of
the Home Address option, and the mapping between the home address
and care-of address indicated by the Home Address option Update. This field MUST NOT be
used as a basis for routing subsequent packets sent by this receiving
node.
No special authentication of zero if the Home Address option
Registration (H) bit is required,
except that if not set in the IPv6 header of a packet Binding Update. The
Prefix Length field is covered set by
authentication, then that authentication MUST also cover the Home
Address option; this coverage is achieved automatically by sending mobile node to the
definition
(nonzero) length of the Option Type code for its subnet prefix in its home address
(given in the Home Address option,
since it indicates that the option is included in the authentication
computation. If the packet carries no IP authentication, then packet) to request
its home agent to use the
contents of interface identifier in the Home Address option, as well as mobile
node's home address (the remaining low-order bits after the Source Address
field or any
indicated subnet prefix) to form all other field in home addresses for
the IPv6 header, may have been forged or
altered during transit. Upon receipt of a packet containing a Home
Address option, the receiving mobile node replaces on the Source Address in home link. The home agent becomes the IPv6 header with
home agent not only for the Home Address individual home address given in the Home Address option.
By requiring that any authentication of the IPv6 header
this binding, but also cover for all other home addresses for this
mobile node formed from this interface identifier. That is,
for each on-link prefix on the Home Address option, home link, the security of home agent uses
the Source Address field in interface identifier to form other valid addresses for the IPv6 header is not compromised by
mobile node on the presence of home link, and acts as a Home Address
option. Security issues related to home agent also
for those addresses. In addition, the Home home agent forms the
link-local address and site-local address corresponding to
this interface identifier, and defends each for purposes of
Duplicate Address option Detection. Details of this operation are
discussed further
described in Section 13.
The three highest-order bits of 9.3.
Sequence Number
Used by the Option Type are encoded receiving node to
indicate specific processing of the option [5]. For sequence Binding Updates and by
the Home Address
option, these three bits are set sending node to 110, indicating that any match a returned Binding Acknowledgement
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node processing 4 August 1998
with this option that does not recognize the Option Type
must discard the packet and, only if the packet's Destination Address
was not Binding Update. Each Binding Update sent by a multicast address, return an ICMP Parameter Problem,
Code 2, message mobile
node MUST use a Sequence Number greater than the Sequence
Number value sent in the previous Binding Update (if any) to
the packet's Source Address; and same destination address (modulo 2**16).
Lifetime
32-bit unsigned integer. The number of seconds remaining
before the binding must be considered expired. A value of all
one bits (0xffffffff) indicates infinity. A value of zero
indicates that the data
within Binding Cache entry for the option cannot change en-route to mobile node
should be deleted.
Care-of Address
This field in the packet's final
destination.
Extensions to Binding Update is optional and is only
present when the Home Care-of Address option format may be included after Present (C) bit is set. If
present, it gives the fixed portion care-of address of the Home Address option specified above.
The presence of such extensions mobile node for
this binding. For most Binding Updates sent, it is expected
that this field will not be indicated by present, and instead that the Option
Length field. When
care-of address for the Option Length is greater than 8 octets, binding will be given by the remaining octets are interpreted as extensions. Currently, no
extensions have been defined.
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Address field in IPv6 13 March 1998
6. Modifications to IPv6 Neighbor Discovery
6.1. Router Advertisement Message Format
Mobile IPv6 requires the addition of packet's IPv6 header.
Any packet that includes a single flag bit to the format
of Binding Update option MUST also include
a Router Advertisement message [11], for use in the dynamic Home Address option. The home
agent address discovery mechanism (Sections 9.2 and 10.4). The
Router Advertisement message format of the mobile node in the
binding given in the Binding Update option is thus modified as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Code | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cur Hop Limit |M|O|H| Reserved| Router Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reachable Time |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Retrans Timer |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Options ...
+-+-+-+-+-+-+-+-+-+-+-+-
This format represents indicated by the following changes over that specified for
Neighbor Discovery [11]: Home Agent (H)
The
Address field in the Home Agent (H) bit is set Address option in a Router Advertisement to
indicate that the router sending this Router Advertisement is
also functioning as a Mobile IP home agent.
Reserved
Reduced from a 6-bit field to packet.
Any packet that includes a 5-bit Binding Update option MUST also include
either an AH [8] or ESP [9] header providing sender authentication,
data integrity protection, and replay protection.
If the care-of address in the binding (either the Care-of Address
field to account for in the
addition of Binding Update option or the Home Agent (H) bit.
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the packet's IPv6 13 March 1998
6.2. Advertisement Interval Option Format
The Advertisement Interval option header) is used in Router Advertisement
messages equal to advertise the interval at which this router sends
unsolicited multicast Router Advertisements. Routers operating
as Mobile IP home agents MAY include this option in their Router
Advertisements. A address of the mobile node receiving a Router Advertisement
containing this option SHOULD utilize
node, the specified Advertisement
Interval for that home agent in its movement detection algorithm, as
described in Section 10.2.
This Binding Update option indicates that any existing binding
for the mobile node MUST be silently ignored for other Neighbor Discovery
messages.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertisement Interval |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
6 ???
Length
1
Reserved
This deleted. Likewise, if the Lifetime
field in the Binding Update option is unused. It equal to 0, the Binding Update
option indicates that any existing binding for the mobile node MUST
be initialized to zero by deleted. In each of these cases, a Binding Cache entry for the
sender and
mobile node MUST NOT be ignored by created in response to receiving the receiver.
Advertisement Interval
32-bit unsigned integer. Binding
Update.
The maximum time, in milliseconds,
between successive unsolicited router Router Advertisement
messages last Sequence Number value sent to a destination in a Binding
Update is stored by this router on this network interface. Using the conceptual router configuration variables defined by
Neighbor Discovery [11], this field MUST be equal to mobile node in its Binding Update List entry
for that destination; the last Sequence Number value
MaxRtrAdvInterval, expressed received from
a mobile node in milliseconds.
Johnson and Perkins Expires 13 September 1998 [Page 28] a Binding Update is stored by a correspondent node
in its Binding Cache entry for that mobile node. Thus, the mobile
node's and the correspondent node's knowledge of the last sequence
number expire at the same time. If the sending mobile node has no
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6.3. Changes to MinRtrAdvInterval Limits
The Neighbor Discovery protocol specification [11] limits routers to
a minimum interval of 3 seconds between
Binding Update List entry, the Sequence Number may start at any
value; if the receiving correspondent node has no Binding Cache entry
for the sending unsolicited multicast
Router Advertisement messages from mobile node, it MUST accept any given network interface
(MinRtrAdvInterval), stating that:
"Routers generate Router Advertisements frequently enough
that hosts will learn of their presence within Sequence Number value
in a few
minutes, but not frequently enough received Binding Update from this mobile node.
The three highest-order bits of the Option Type are encoded to rely on an absence
indicate specific processing of advertisements the option [5]. For the Binding
Update option, these three bits are set to detect router failure; a separate
Neighbor Unreachability Detection algorithm provides failure
detection."
This limitation, however, is 110, indicating that any
IPv6 node processing this option that does not suitable to providing timely
movement detection for mobile nodes. Mobile nodes detect their
own movement by learning recognize the presence of new routers as Option
Type must discard the mobile
node moves into wireless transmission range of them (or physically
connects to packet and, only if the packet's Destination
Address was not a new wired network), multicast address, return an ICMP Parameter
Problem, Code 2, message to the packet's Source Address; and by learning that previous
routers the
data within the option cannot change en-route to the packet's final
destination.
Extensions to the Binding Update option format may be included after
the fixed portion of the Binding Update option specified above.
The presence of such extensions will be indicated by the Option
Length field. When the Option Length is greater than the length
defined above, the remaining octets are interpreted as extensions.
Currently, no longer reachable. Mobile nodes extensions have been defined.
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5.2. Binding Acknowledgement Option Format
The Binding Acknowledgement destination option is used to acknowledge
receipt of a Binding Update option (Section 5.1). When a node
receives a packet containing a Binding Update option, with this
node being the destination of the packet (only the destination node
processes the option since it is a destination option), this node
MUST be able return a Binding Acknowledgement to
quickly detect when they move the source of the packet,
if the Acknowledge (A) bit is set in the Binding Update. As a
destination option, this node MAY included it in any existing packet
being sent to the mobile node or MAY send it in a packet by itself; a
packet containing a Binding Acknowledgement is sent in the same way
as any packet to a mobile node (Section 8.9).
The Binding Acknowledgement option is encoded in type-length-value
(TLV) format as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+
| Option Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Length | Status | Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Refresh |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
. .
. Home Agents List .
. .
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Option Type
2 ???
Option Length
8-bit unsigned integer. Length of the option, in octets,
excluding the Option Type and Option Length fields. This field
MUST be set to 11, except when the Status field is equal to 135
(dynamic home agent address discovery response), in which case
this field MUST be set to 11 + 16 * N, where N is the number of
IP addresses included in the Home Agents List field; the Home
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Agents List field MUST NOT be included in the option if the
Status field is not set to 135.
Status
8-bit unsigned integer indicating the disposition of the
Binding Update. Values of the Status field less than 128
indicate that the Binding Update was accepted by the receiving
node. The following such Status values are currently defined:
0 Binding Update accepted
Values of the Status field greater than or equal to 128
indicate that the Binding Update was rejected by the receiving
node. The following such Status values are currently defined:
128 Reason unspecified
129 Poorly formed Binding Update
130 Administratively prohibited
131 Insufficient resources
132 Home registration not supported
133 Not home subnet
134 Sequence Number field value too small
135 Dynamic home agent address discovery response
136 Incorrect interface identifier length
137 Not home agent for this mobile node
Up-to-date values of the Status field are to be specified in
the most recent "Assigned Numbers" [21].
Sequence Number
The Sequence Number in the Binding Acknowledgement is copied
from the Sequence Number field in the Binding Update being
acknowledged, for use by the mobile node in matching this
Acknowledgement with an outstanding Binding Update.
Lifetime
The granted lifetime for which this node will attempt to retain
the entry for this mobile node in its Binding Cache. If the
node sending the Binding Acknowledgement is serving as the
mobile node's home agent, the Lifetime period also indicates
the period for which this node will continue this service; if
the mobile node requires home agent service from this node
beyond this period, the mobile node MUST send a new Binding
Update to it before the expiration of this period (even if
it is not changing its primary care-of address), in order to
extend the lifetime. The value of this field is undefined
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if the Status field indicates that the Binding Update was
rejected.
Refresh
The recommended interval at which the mobile node SHOULD send
a new Binding Update to this node in order to "refresh" the
mobile node's binding in this node's Binding Cache. This
refreshing of the binding is useful in case the node fails and
loses its cache state. The Refresh period is determined by
the node sending the Binding Acknowledgement (the node caching
the binding). If this node is serving as the mobile node's
home agent, the Refresh value may be set, for example, based on
whether the node stores its Binding Cache in volatile storage
or in nonvolatile storage. If the node sending the Binding
Acknowledgement is not serving as the mobile node's home agent,
the Refresh period SHOULD be set equal to the Lifetime period
in the Binding Acknowledgement; even if this node loses this
cache entry due to a failure of the node, packets from it can
still reach the mobile node through the mobile node's home
agent, causing a new Binding Update to this node to allow it
to recreate this cache entry. The value of this field is
undefined if the Status field indicates that the Binding Update
was rejected.
Home Agents List
A list of home agents on the home link for the mobile node to
which this Binding Acknowledgement is sent. This field MUST
NOT be present (zero addresses listed) unless the Binding
Acknowledgement is sent in response to an anycast Binding
Update sent by this mobile node attempting dynamic home agent
address discovery. In this case, the Status field MUST be
set to 135 (dynamic home agent address discovery response).
The construction of the Home Agents List field in a Binding
Acknowledgement is defined in Section 9.2.
Any packet that includes a Binding Acknowledgement option MUST
also include either an AH [8] or ESP [9] header providing sender
authentication, data integrity protection, and replay protection.
If the node returning the Binding Acknowledgement accepted the
Binding Update for which the Acknowledgement is being returned (the
value of the Status field in the Acknowledgement is less than 128),
this node will have an entry for the mobile node in its Binding Cache
and MUST use this entry (which includes the care-of address received
in the Binding Update) in sending the packet containing the Binding
Acknowledgement to the mobile node. The details of sending this
packet to the mobile node are the same as for sending any packet to a
mobile node using a binding, and are described in Section 8.9. The
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packet is sent using a Routing header, routing the packet to the
mobile node by way of its care-of address recorded in the Binding
Cache entry.
If the node returning the Binding Acknowledgement instead
rejected the Binding Update (the value of the Status field in the
Acknowledgement is greater than or equal to 128), this node MUST
similarly use a Routing header in sending the packet containing the
Binding Acknowledgement, as described in Section 8.9, but MUST NOT
use its Binding Cache in forming the IP header or Routing header
in this packet. Rather, the care-of address used by this node in
sending the packet containing the Binding Acknowledgement MUST be
copied from the care-of address received in the rejected Binding
Update; this node MUST NOT modify its Binding Cache in response
to receiving this rejected Binding Update and MUST ignore its
Binding Cache in sending the packet in which it returns this Binding
Acknowledgement. The packet is sent using a Routing header, routing
the packet to the home address of the rejected Binding Update by
way of the care-of address indicated in the packet containing the
Binding Update. When sending a Binding Acknowledgement to reject a
Binding Update, the Binding Acknowledgement MUST be sent in an IPv6
packet containing no payload (with the Next Header field in the last
extension header in the packet set to indicate "No Next Header" [5]).
The three highest-order bits of the Option Type are encoded to
indicate specific processing of the option [5]. For the Binding
Acknowledgement option, these three bits are set to 000, indicating
that any IPv6 node processing this option that does not recognize the
Option Type must skip over this option and continue processing the
header, and that the data within the option cannot change en-route to
the packet's final destination.
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5.3. Binding Request Option Format
The Binding Request destination option is used to request a mobile
node's binding from the mobile node. As a destination option, it
MAY be included in any existing packet being sent to the mobile
node or MAY be sent in a packet by itself; a packet containing a
Binding Request option is sent in the same way as any packet to a
mobile node (Section 8.9). When a mobile node receives a packet
containing a Binding Request option, it SHOULD return a Binding
Update (Section 5.1) to the source of the Binding Request.
The Binding Request option is encoded in type-length-value (TLV)
format as follows:
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Type | Option Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Option Type
3 ???
Option Length
8-bit unsigned integer. Length of the option, in octets,
excluding the Option Type and Option Length fields. For the
current definition of the Binding Request option, this field
MUST be set to 0.
The three highest-order bits of the Option Type are encoded to
indicate specific processing of the option [5]. For the Binding
Request option, these three bits are set to 000, indicating that any
IPv6 node processing this option that does not recognize the Option
Type must skip over this option and continue processing the header,
and that the data within the option cannot change en-route to the
packet's final destination.
Extensions to the Binding Request option format may be included after
the fixed portion of the Binding Request option specified above.
The presence of such extensions will be indicated by the Option
Length field. When the Option Length is greater than 0 octets,
the remaining octets are interpreted as extensions. Currently, no
extensions have been defined.
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5.4. Home Address Option Format
The Home Address destination option is used in a packet sent by a
mobile node while away from home, to inform the recipient of that
packet of the mobile node's home address. For packets sent by a
mobile node while away from home, the mobile node generally uses
one of its care-of addresses as the Source Address in the packet's
IPv6 header. By including a Home Address option in the packet, the
correspondent node receiving the packet is able to substitute the
mobile node's home address for this care-of address when processing
the packet, thus making the use of the care-of address transparent to
the correspondent node.
The Home Address option is encoded in type-length-value (TLV) format
as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Type | Option Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Home Address +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Option Type
196 ???
Option Length
8-bit unsigned integer. Length of the option, in octets,
excluding the Option Type and Option Length fields. For the
current definition of the Home Address option, this field MUST
be set to 16.
Home Address
The home address of the mobile node sending the packet.
The inclusion of a Home Address option in a packet affects the
receiving node's processing of only this single packet; no state is
created or modified in the receiving node as a result of receiving a
Home Address option in a packet. In particular, the presence of a
Home Address option in a received packet MUST NOT alter the contents
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of the receiver's Binding Cache and MUST NOT cause any changes in the
routing of subsequent packets sent by this receiving node.
No authentication of the Home Address option is required, except that
if the IPv6 header of a packet is covered by authentication, then
that authentication MUST also cover the Home Address option; this
coverage is achieved automatically by the definition of the Option
Type code for the Home Address option, since it indicates that the
data within the option cannot change en-route to the packet's final
destination, and thus the option is included in the authentication
computation. If the packet carries no IP authentication, then the
contents of the Home Address option, as well as the Source Address
field or any other field in the IPv6 header, may have been forged or
altered during transit.
Upon receipt of a packet containing a Home Address option, the
receiving node replaces the Source Address in the IPv6 header with
the Home Address in the Home Address option. By requiring that any
authentication of the IPv6 header also cover the Home Address option,
the security of the Source Address field in the IPv6 header is not
compromised by the presence of a Home Address option. Security
issues related to the Home Address option are discussed further in
Section 13.
The three highest-order bits of the Option Type are encoded to
indicate specific processing of the option [5]. For the Home Address
option, these three bits are set to 110, indicating that any IPv6
node processing this option that does not recognize the Option Type
must discard the packet and, only if the packet's Destination Address
was not a multicast address, return an ICMP Parameter Problem,
Code 2, message to the packet's Source Address; and that the data
within the option cannot change en-route to the packet's final
destination.
Extensions to the Home Address option format may be included after
the fixed portion of the Home Address option specified above.
The presence of such extensions will be indicated by the Option
Length field. When the Option Length is greater than 8 octets,
the remaining octets are interpreted as extensions. Currently, no
extensions have been defined.
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6. Modifications to IPv6 Neighbor Discovery
6.1. Modified Router Advertisement Message Format
Mobile IPv6 modifies the format of the Router Advertisement
message [13] by the addition of a single flag bit for use in the
dynamic home agent address discovery mechanism (Sections 9.2
and 10.6). The format of the Router Advertisement message is
as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Code | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cur Hop Limit |M|O|H| Reserved| Router Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reachable Time |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Retrans Timer |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Options ...
+-+-+-+-+-+-+-+-+-+-+-+-
This format represents the following changes over that originally
specified for Neighbor Discovery [13]:
Home Agent (H)
The Home Agent (H) bit is set in a Router Advertisement to
indicate that the router sending this Router Advertisement is
also functioning as a Mobile IP home agent.
Reserved
Reduced from a 6-bit field to a 5-bit field to account for the
addition of the Home Agent (H) bit.
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6.2. Modified Prefix Information Option Format
Mobile IPv6 requires knowledge of a router's global address for two
reasons:
- To allow a home agent (a router) to learn the address of all
other home agents on the link for which it is proving home agent
service, for use in building its Home Agents List as part of the
dynamic home agent address discovery mechanism (Sections 9.2
and 10.6).
- To allow a mobile node to send a Binding Update to its previous
default router, after moving to a new subnet and acquiring a new
care-of address (Section 10.8).
However, Neighbor Discovery [13] only advertises a router's
link-local address, by requiring this address to be used as the IP
Source Address of each Router Advertisement.
Mobile IPv6 extends Neighbor Discovery to allow a router to easily
and efficiently advertise its global address, by the addition of a
single flag bit in the format of a Prefix Information option for
use in Router Advertisement messages. The format of the Prefix
Information option is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Prefix Length |L|A|R|Reserved1|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Valid Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Preferred Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Prefix +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
This format represents the following changes over that originally
specified for Neighbor Discovery [13]:
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Router Address (R)
1-bit router address flag. When set, indicates that the
Prefix field, in addition to advertising the indicated prefix,
contains a complete IP address assigned to the sending router.
This router IP address has the same scope and conforms to the
same lifetime values as the advertised prefix. This use of
the Prefix field is compatible with its use in advertising
the prefix itself, since prefix advertisement uses only the
leading number Prefix bits specified by the Prefix Length
field. Interpretation of this flag bit is thus independent
of the processing required for the On-Link (L) and Autonomous
Address-Configuration (A) flag bits.
Reserved1
Reduced from a 6-bit field to a 5-bit field to account for the
addition of the Router Address (R) bit.
In a solicited Router Advertisement, a router MUST include at least
one Prefix Information option with the Router Address (R) bit set.
Neighbor Discovery specifies that, if including all options in a
Router Advertisement causes the size of the Advertisement to exceed
the link MTU, multiple Advertisements can be sent, each containing
a subset of the options [13]. In this case, at least one of these
multiple Advertisements begin sent instead of a single larger
solicited Advertisement, MUST include a Prefix Information option
with the Router Address (R) bit set.
All routers SHOULD include at least one Prefix Information option
with the Router Address (R) bit set, in each unsolicited multicast
Router Advertisement that they send. If multiple Advertisements
are being sent instead of a single larger unsolicited multicast
Advertisement, at least one of these multiple Advertisements SHOULD
include a Prefix Information option with the Router Address (R) bit
set.
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6.3. New Advertisement Interval Option Format
Mobile IPv6 defines a new Advertisement Interval option, used in
Router Advertisement messages to advertise the interval at which the
sending router sends unsolicited multicast Router Advertisements.
The format of the Advertisement Interval option is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertisement Interval |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
6 ???
Length
8-bit unsigned integer. The length of the option (including
the type and length fields) in units of 8 octets. The value of
this field MUST be 1.
Reserved
This field is unused. It MUST be initialized to zero by the
sender and MUST be ignored by the receiver.
Advertisement Interval
32-bit unsigned integer. The maximum time, in milliseconds,
between successive unsolicited router Router Advertisement
messages sent by this router on this network interface. Using
the conceptual router configuration variables defined by
Neighbor Discovery [13], this field MUST be equal to the value
MaxRtrAdvInterval, expressed in milliseconds.
Routers MAY include this option in their Router Advertisements. A
mobile node receiving a Router Advertisement containing this option
SHOULD utilize the specified Advertisement Interval for that router
in its movement detection algorithm, as described in Section 10.3.
This option MUST be silently ignored for other Neighbor Discovery
messages.
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6.4. New Home Agent Information Option Format
Mobile IPv6 defines a new Home Agent Information option, used in
Router Advertisement messages sent by a home agent to advertise
information specific to this router's functionality as a home agent.
The format of the Home Agent Information option is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Home Agent Preference | Home Agent Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
7 ???
Length
8-bit unsigned integer. The length of the option (including
the type and length fields) in units of 8 octets. The value of
this field MUST be 1.
Reserved
This field is unused. It MUST be initialized to zero by the
sender and MUST be ignored by the receiver.
Home Agent Preference
16-bit signed, twos-complement integer. The preference
for the home agent sending this Router Advertisement, for
use in ordering the Home Agents List returned in a Binding
Acknowledgement; higher values mean more preferable. If this
option is not included in a Router Advertisement in which the
Home Agent (H) bit is set, the preference value for this home
agent SHOULD be considered to be 0. Values greater than 0
indicate a home agent more preferable than this default value,
and values less than 0 indicate a less preferable home agent.
Home Agent Lifetime
16-bit unsigned integer. The lifetime associated with the home
agent in units of seconds. The maximum value corresponds to
18.2 hours. A value of 0 MUST NOT be used. The Home Agent
Lifetime applies only to this router's usefulness as a home
agent; it does not apply to information contained in other
message fields or options. If this option is not included in
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a Router Advertisement in which the Home Agent (H) bit is set,
the lifetime for this home agent SHOULD be considered to be the
same as the Router Lifetime specified in the main body of the
Router Advertisement message.
Home agents MAY include this option in their Router Advertisements.
This option MUST NOT be included in a Router Advertisement in which
the Home Agent (H) bit (Section 6.1) is not set.
This option MUST be silently ignored for other Neighbor Discovery
messages.
If both the Home Agent Preference and Home Agent Lifetime are set
to their default values specified above, this option SHOULD NOT be
included in the Router Advertisement messages sent by this home
agent.
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6.5. Changes to Sending Router Advertisements
The Neighbor Discovery protocol specification [13] limits routers to
a minimum interval of 3 seconds between sending unsolicited multicast
Router Advertisement messages from any given network interface
(limited by MinRtrAdvInterval and MaxRtrAdvInterval), stating that:
"Routers generate Router Advertisements frequently enough
that hosts will learn of their presence within a few
minutes, but not frequently enough to rely on an absence
of advertisements to detect router failure; a separate
Neighbor Unreachability Detection algorithm provides failure
detection."
This limitation, however, is not suitable to providing timely
movement detection for mobile nodes. Mobile nodes detect their
own movement by learning the presence of new routers as the mobile
node moves into wireless transmission range of them (or physically
connects to a new wired network), and by learning that previous
routers are no longer reachable. Mobile nodes MUST be able to
quickly detect when they move to a link served by a new router, so
that they can acquire a new care-of address and send Binding Updates
to register this care-of address with their home agent and to notify
correspondent nodes as needed.
Thus, to provide good support for mobile nodes, Mobile IPv6 relaxes
this limit such that routers MAY send unsolicited multicast Router
Advertisements more frequently. In particular, on network interfaces
where the router is expecting to provide service to visiting mobile
nodes (e.g., wireless network interfaces), or on which it is serving
as a home agent to one or more mobile nodes (who may return home and
need to hear its Advertisements), the home agent SHOULD be configured
with a smaller MinRtrAdvInterval value and MaxRtrAdvInterval value,
to allow sending of unsolicited multicast Router Advertisements more
often. Recommended values for these limits are:
- MinRtrAdvInterval 0.5 seconds
- MaxRtrAdvInterval 1.5 seconds
Use of these modified limits MUST be configurable, and specific
knowledge of the type of network interface in use SHOULD be taken
into account in configuring these limits for each network interface.
When sending unsolicited multicast Router Advertisements more
frequently than the standard limit on unsolicited multicast
Advertisement frequency, the sending router need not include all
options in each of these Advertisements, but it SHOULD include at
least one Prefix Information option with the Router Address (R) bit
set (Section 6.2) in each.
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6.6. Changes to Sending Router Solicitations
In addition to the limit on routers sending unsolicited multicast
Router Advertisement messages (Section 6.5), Neighbor Discovery
defines limits on nodes sending Router Solicitation messages, such
that a node SHOULD send no more than 3 Router Solicitations, and that
these 3 transmissions SHOULD be spaced at least 4 seconds apart.
However, these limits prevent a mobile node from finding a new
default router (and thus a new care-of address) quickly as it moves
about.
Mobile IPv6 relaxes this limit such that, while a mobile node is away
from home, it MAY send Router Solicitations more frequently. The
following limits for sending Router Solicitations are recommended for
mobile nodes while away from home:
- A mobile node that is not configured with any current care-of
address (e.g., the mobile node has moved since its previous
care-of address was configured), MAY send more than the defined
Neighbor Discovery limit of MAX_RTR_SOLICITATIONS Router
Solicitations.
- The rate at which a mobile node sends Router Solicitations MUST
be limited, although a mobile node MAY send Router Solicitations
more frequently than the defined Neighbor Discovery limit of
RTR_SOLICITATION_INTERVAL seconds. The minimum interval MUST
be configurable, and specific knowledge of the type of network
interface in use SHOULD be taken into account in configuring this
limit for each network interface. A recommended minimum interval
is 1 second.
- After sending at most MAX_RTR_SOLICITATIONS Router Solicitations,
a mobile node MUST reduce the rate at which it sends subsequent
Router Solicitations. Subsequent Router Solicitations SHOULD
be sent using a binary exponential backoff mechanism, doubling
the interval between consecutive Router Solicitations, up to a
maximum interval. The maximum interval MUST be configurable and
SHOULD be chosen appropriately based on the characteristics of
the type of network interface in use.
- While still searching for a new default router and care-of
address, a mobile node MUST NOT increase the rate at which it
sends Router Solicitations unless it has received a positive
indication (such as from lower network layers) that it has moved
to a new link. After successfully acquiring a new care-of
address, the mobile node SHOULD also increase the rate at which
it will send Router Solicitations when it next begins searching
for a new default router and care-of address.
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- A mobile node that is currently configured with a care-of
address SHOULD NOT send Router Solicitations, until its movement
detection algorithm (Section 10.3) determines that it has moved
and that its current care-of address might no longer be valid.
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7. Requirements for IPv6 Nodes
Mobile IPv6 places some special requirements on the functions
provided by different types of IPv6 nodes. This section summarizes
those requirements, identifying the functionality each requirement
is intended to support. Further details on this functionality is
provided in the following sections.
7.1. Requirements for All IPv6 Hosts and Routers
Since any IPv6 node may at any time be a correspondent node of a
mobile node, either sending a packet to a mobile node or receiving a
packet from a mobile node, the following requirements apply to ALL
IPv6 nodes (whether host or router, whether mobile or stationary):
- Every IPv6 node MUST be able to process a Home Address option
received in any IPv6 packet.
- Every IPv6 node SHOULD be able to process a Binding Update option
received in a packet, and to return a Binding Acknowledgement
option if the Acknowledge (A) bit is set in the received Binding
Update.
- Every IPv6 node SHOULD be able to maintain a Binding Cache of the
bindings received in accepted Binding Updates.
7.2. Requirements for All IPv6 Routers
The following requirements apply to all IPv6 routers, even those not
serving as a home agent for Mobile IPv6:
- Every IPv6 router SHOULD be able to send an Advertisement
Interval option in its Router Advertisements, to aid movement
detection by mobile nodes. The use of this option in Router
Advertisements MUST be configurable.
- Every IPv6 router SHOULD be able to support sending unsolicited
multicast Router Advertisements at the faster rate described in
Section 6.5. The use of this faster rate MUST be configurable.
7.3. Requirements for IPv6 Home Agents
In order for a mobile node to operate correctly while away from home,
at least one IPv6 router on the mobile node's home link must function
as a home agent for the mobile node. The following additional
requirements apply to all IPv6 routers capable of serving as a home
agent:
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- Every home agent MUST be able to maintain an entry in its Binding
Cache for each mobile node for which it is serving as the home
agent. Each such Binding Cache entry records the mobile node's
binding with its primary care-of address and is marked as a "home
registration".
- Every home agent MUST be able to intercept packets (using proxy
Neighbor Discovery) addressed to a mobile node for which it is
currently serving as the home agent, on that mobile node's home
link, while the mobile node is away from home.
- Every home agent MUST be able to encapsulate such intercepted
packets in order to tunnel them to the primary care-of address
for the mobile node indicated in its binding in the home agent's
Binding Cache.
- Every home agent MUST be able to return a Binding Acknowledgement
option in response to a Binding Update option received with the
Acknowledge (A) bit set.
- Every home agent MUST be able to accept packets addressed to the
Home-Agents anycast address for the subnet on which it is serving
as a home agent, and MUST be able to participate in dynamic home
agent address discovery (Section 9.2).
7.4. Requirements for IPv6 Mobile Nodes
Finally, the following requirements apply to all IPv6 nodes capable
of functioning as mobile nodes:
- Every IPv6 mobile node MUST be able to perform IPv6
decapsulation [4].
- Every IPv6 mobile node MUST support sending Binding Update
options, as specified in Sections 10.5, 10.7, and 10.8; and MUST
be able to receive and process Binding Acknowledgement options,
as specified in Section 10.11.
- Every IPv6 mobile node MUST support use of the dynamic home agent
address discovery mechanism, as described in Section 10.6.
- Every IPv6 mobile node MUST maintain a Binding Update List in
which it records the IP address of each other node to which it
has sent a Binding Update, for which the Lifetime sent in that
binding has not yet expired.
- Every IPv6 mobile node MUST support receiving a Binding Request
option, by responding with a Binding Update option.
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- Every IPv6 mobile node MUST support sending packets containing a
Home Address option; this option MUST be included in all packets
sent while away from home, if the packet would otherwise have
been sent with the mobile node's home address as the IP Source
Address.
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8. Correspondent Node Operation
A correspondent node is any node communicating with a mobile node.
The correspondent node, itself, may be stationary or mobile, and may
possibly also be functioning as a home agent for Mobile IPv6. The
procedures in this section thus apply to all IPv6 nodes.
8.1. Receiving Packets from a Mobile Node
Packets sent by a mobile node while away from home generally include
a Home Address option. When any node receives a packet containing
a Home Address option, it MUST process the option in a manner
consistent with copying the Home Address field from the Home Address
option into the IPv6 header, replacing the original value of the
Source Address field there.
Further processing of such a packet (e.g., at the transport layer)
thus need not know that the original Source Address was a care-of
address, or that the Home Address option was used in the packet.
Since the sending mobile node uses its home address at the transport
layer when sending such a packet, the use of the care-of address
and Home Address option is transparent to both the mobile node and
the correspondent node above the level of the Home Address option
generation and processing.
8.2. Receiving Binding Updates
Upon receiving a Binding Update option in some packet, the receiving
node MUST validate the Binding Update according to the following
tests:
- The packet contains a valid AH [8] or ESP [9] header that
provides sender authentication, integrity protection, and replay
protection.
- The packet MUST contain a valid Home Address option. The home
address for the binding is specified by the Home Address field of
the Home Address option.
- The Option Length field in the Binding Update option is greater
than or equal to the length specified in Section 5.1.
- The Sequence Number field in the Binding Update option is greater
than the Sequence Number received in the previous Binding Update
for this home address, if any. The Sequence Number comparison is
performed modulo 2**16.
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Any Binding Update not satisfying all of these tests MUST be
silently ignored, and the packet carrying the Binding Update MUST be
discarded.
If the Binding Update is valid according to the tests above, then the
Binding Update is processed further as follows:
- If the Destination Address in the packet's IPv6 header is the
Home-Agents anycast address for a local prefix and this address
is assigned to one of this node's network interfaces, then the
mobile node sending this Binding Update is attempting dynamic
home agent address discovery. Processing for this type of
received Binding Update is described in Section 9.2. (If the
Destination Address is not assigned to one of this node's network
interfaces, then the packet would have been forwarded as a normal
packet and the Binding Update, as a destination option, would not
be processed in any way by this node.)
- If the Lifetime specified in the Binding Update is nonzero and
the specified Care-of Address is not equal to the home address
for the binding (as given in the Home Address option in the
packet), then this is a request to cache a binding for the
mobile node. If the Home Registration (H) bit is set in the
Binding Update, the Binding Update is processed according to the
procedure specified in Section 9.3; otherwise, it is processed
according to the procedure specified in Section 8.3.
- If the Lifetime specified in the Binding Update is zero or the
specified Care-of Address matches the home address for the
binding, then this is a request to delete the mobile node's
cached binding. If the Home Registration (H) bit is set in the
Binding Update, the Binding Update is processed according to the
procedure specified in Section 9.4; otherwise, it is processed
according to the procedure specified in Section 8.4.
8.3. Requests to Cache a link served by Binding
When a new router, so
that they can acquire node receives a new care-of address and send Binding Updates
to register this care-of address with their home agent Update, it MUST validate it and to notify
correspondent nodes as needed.
Thus, routers serving as Mobile IP home agents MAY send unsolicited
multicast Router Advertisements more frequently than this limit. In
particular, on network interfaces where
determine the home agent is expecting
to provide service type of Binding Update according to visiting mobile nodes (e.g., wireless network
interfaces), the home agent SHOULD be configured with steps described
in Section 8.2. This section describes the processing of a smaller
MinRtrAdvInterval value valid
Binding Update that requests a node to allow sending of unsolicited multicast
Router Advertisements more often. A recommended maximum rate is
once per second, although specific knowledge of cache a mobile node's binding,
for which the type of network
interface Home Registration (H) bit is not set in use the Binding
Update.
In this case, the receiving node SHOULD be taken into account create a new entry in configuring its
Binding Cache for this
limit mobile node (or update its existing Binding
Cache entry for each network interface. this mobile node, if such an entry already exists).
The home address of the mobile node is taken from the Home Address
field in the packet's Home Address option. The new Binding Cache
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7. Requirements for IPv6 Nodes
Mobile IPv6 places some special requirements on IPv6 4 August 1998
entry records the association between this home address and the
care-of address for the binding, as specified in either the Care-of
Address field of the Binding Update or in the functions
provided by different IPv6 nodes. This section summarizes those
requirements, identifying Source Address field
in the functionality each requirement is
intended packet's IPv6 header. Any Binding Cache entry created or
updated in response to support. Further details on processing this functionality is
provided Binding Update MUST be deleted
after the expiration of the Lifetime period specified in the following sections.
7.1. Requirements for All IPv6 Hosts and Routers
Since any IPv6 node may at any time be Binding
Update.
8.4. Requests to Delete a Binding
When a correspondent node receives a Binding Update, it MUST validate it and
determine the type of Binding Update according to the steps described
in Section 8.2. This section describes the processing of a
mobile node, either sending valid
Binding Update that requests a packet node to delete a mobile node or receiving a
packet node's binding
from a its Binding Cache, for which the Home Registration (H) bit is
not set in the Binding Update.
In this case, the receiving node MUST delete any existing entry in
its Binding Cache for this mobile node, node. The home address of the following requirements pertain to ALL
IPv6 nodes (whether host or router, whether
mobile or stationary):
- Every IPv6 node MUST be able to process a is taken from the Home Address option
received field in a packet.
- Every IPv6 node SHOULD be able to process a the packet's Home
Address option.
8.5. Sending Binding Update option
received in Acknowledgements
When any node receives a packet, and to return packet containing a Binding Acknowledgement Update option if requested.
- Every IPv6 node
in which the Acknowledge (A) bit is set, it SHOULD be able to maintain return a Binding Cache
Acknowledgement option acknowledging receipt of the
bindings received in accepted Binding Updates.
7.2. Requirements for IPv6 Home Agents
In order for a mobile Update.
If the node to operate correctly while away from
home, at least one IPv6 router in accepts the mobile node's home link must
function as a home agent Binding Update and creates or updates an
entry in its Binding Cache for this binding, the mobile node. The following special
requirements pertain to all IPv6 routers capable of serving as a home
agent:
- Every home agent Status field in
the Binding Acknowledgement MUST be able set to maintain a value less than 128;
if the node rejects the Binding Update and does not create or
update an entry for this binding, the Status field in its the Binding
Cache for each mobile node
Acknowledgement MUST be set to a value greater than or equal to 128.
Specific values for the Status field are described in Section 5.2 and
in the most recent "Assigned Numbers" [21].
As described in Section 5.2, the packet in which it the Binding
Acknowledgement is serving returned MUST include either an AH [8] or ESP [9]
header providing sender authentication, data integrity protection,
and replay protection; and the packet MUST be sent using a Routing
header in the same way as any other packet sent to a mobile node
using a care-of address (even if the home
agent. Each such Binding Cache entry records binding was rejected), as
described in Section 8.9. The packet is routed first to the mobile node's
binding with its primary care-of
address contained in the Binding Update being acknowledged, and is marked as a "home
registration".
- Every home agent MUST be able
then to intercept packets (using proxy
Neighbor Discovery) on the local subnet addressed to a mobile
node for which it is currently serving as the node's home agent while address. This use of the Routing
header ensures that mobile node is away from home.
- Every home agent MUST the Binding Acknowledgement will be able to encapsulate such intercepted
packets in order to tunnel them routed to the primary care-of address
for
current location of the mobile node indicated in its binding. sending the Binding Update, whether the
Binding Update was accepted or rejected.
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- Every home agent MUST be able to return a
8.6. Sending Binding Acknowledgement Requests
Entries in response to a node's Binding Update received with the Acknowledge (A)
bit set.
- Every home agent Cache MUST be able to accept deleted when their lifetime
expires. If such an entry is still in active use in sending packets addressed
to the
Home-Agents anycast address for the subnet on which it is serving
as a home agent, and MUST be able mobile node, the next packet sent to participate in dynamic home
agent address discovery (Section 9.2).
7.3. Requirements for IPv6 Mobile Nodes
Finally, the following requirements pertain all IPv6 nodes capable of
functioning as mobile nodes:
- Every IPv6 mobile node MUST will be able
routed normally to perform IPv6
decapsulation [4].
- Every IPv6 the mobile node MUST support sending Binding Updates, as
specified in Sections 10.4, 10.5, and 10.6; and MUST node's home link, where it will be able to
receive
intercepted and process Binding Acknowledgements, as specified in
Section 10.10.
- Every IPv6 tunneled to the mobile node. The mobile node MUST maintain will
then return a Binding Update List in
which it records the IP address of each other node to which the sender, allowing it
has sent to create
a new Binding Update, Cache entry for which sending future packets to the Lifetime sent in that
binding has not yet expired.
- Every IPv6 mobile node MUST support receiving a Binding Request
by responding
node. Communication with a Binding Update.
- Every IPv6 the mobile node MUST support sending packets containing a
Home Address option; this option MUST be included in all packets
sent while away from home, if continues uninterrupted,
but the forwarding of this packet would otherwise have
been sent with through the mobile node's home address as the IP Source
Address.
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8. Correspondent Node Operation
A correspondent node is any node communicating with a delivering packets
to the mobile node.
The correspondent node, itself, may be stationary or mobile, and may
possibly also be functioning as
If the sender knows that the Binding Cache entry is still in active
use, it MAY send a home agent for Mobile IPv6. The
procedures Binding Request option to the mobile node in
an attempt to avoid this section thus apply overhead and latency due to all IPv6 nodes.
8.1. Receiving Packets from deleting and
recreating the Binding Cache entry. Since a Mobile Node
Packets Binding Request is a
destination option, it may, for example, be included in any packet
already being sent by a to the mobile node while away from home generally include node, such as a Home Address option. packet that is part
of ongoing TCP communication with the mobile node. When any the mobile
node receives a packet from some sender containing a Home Address Binding Request
option, it MUST process the returns a Binding Update option to that sender, giving its
current binding and a new lifetime.
8.7. Cache Replacement Policy
Any entry in a manner
consistent with copying the Home Address field from the Home Address
option into the IPv6 header, replacing the original value of node's Binding Cache MUST be deleted after the
Source Address field there. Further processing
expiration of the packet (e.g.,
at Lifetime specified in the transport layer) thus need not know that Binding Update from
which the original Source
Address entry was created or last updated. Conceptually, a care-of address, node
maintains a separate timer for each entry in its Binding Cache. When
creating or that the Home Address option was
used updating a Binding Cache entry in response to a received
and accepted Binding Update, the packet. Since the sending mobile node uses its home
address at sets the transport layer when sending such a packet, timer for this entry
to the use of specified Lifetime period. When a Binding Cache entry's timer
expires, the care-of address and Home Address option is thus transparent to
both node deletes the mobile entry.
Each node's Binding Cache will, by necessity, have a finite size.
A node and MAY use any reasonable local policy for managing the space
within its Binding Cache, except that any entry marked as a "home
registration" (Section 9.3) MUST NOT be deleted from the correspondent node above cache until
the level expiration of
the Home Address option generation and processing.
8.2. Receiving Binding Updates
Upon receiving its lifetime period. When attempting to add a
new "home registration" entry in response to a Binding Update option with
the Home Registration (H) bit set, if insufficient space exists (or
can be reclaimed) in some packet, the receiving node's Binding Cache, the node MUST validate reject
the Binding Update according to the following
tests:
- The packet MUST contain and SHOULD return a valid Home Address option. The home
address for the binding is specified by the Home Address field of Binding Acknowledgement to
the Home Address option.
- The Option Length field sending mobile node, in which the Binding Update option Status field is greater
than or equal set to the length specified in Section 5.1.
- The packet contains 131
(insufficient resources). When otherwise attempting to add a valid AH [7] or ESP [8] header that
provides sender authentication, integrity protection, and replay
protection.
- The Sequence Number field new
entry to its Binding Cache, a node MAY, if needed, choose to drop any
entry already in the its Binding Update option is greater Cache, other than the Sequence Number received a "home registration"
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entry, in order to make space for the previous Binding Update new entry. For example, a
"least-recently used" (LRU) strategy for this home address, if any. The Sequence Number comparison cache entry replacement
among entries not marked as a "home registration" is
performed modulo 2**16. likely to work
well.
Any binding dropped from a node's Binding Update not satisfying all Cache due to lack of these tests MUST cache
space will be
silently ignored, rediscovered and a new cache entry created, if the packet carrying the Binding Update MUST be
discarded.
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binding is still in IPv6 13 March 1998 active use by the node for sending packets. If
the Binding Update is valid according node sends a packet to a destination for which it has dropped the tests above, then the
entry from its Binding Update is processed further as follows:
- If Cache, the Destination Address in packet will be routed normally,
leading to the packet's IPv6 header is mobile node's home link. There, the
Home-Agents anycast address for a local subnet packet will be
intercepted by the mobile node's home agent and this address
is assigned tunneled to one of this node's network interfaces, then the
mobile node sending this node's current primary care-of address. As when a Binding Update
Cache entry is attempting dynamic initially created, this indirect routing to the mobile
node through its home agent address discovery. Processing for this type of
received Binding Update is described will result in Section 9.2. (If the
Destination Address is not assigned mobile node sending
a Binding Update to one of this node's network
interfaces, then sending node when it receives the packet would have been forwarded as tunneled
packet, allowing it to add an entry again for this destination mobile
node to its Binding Cache.
8.8. Receiving ICMP Error Messages
When a correspondent node sends a normal packet and to a mobile node, if the Binding Update, as
correspondent node has a Binding Cache entry for the destination option, would not
be processed in any way by this node.)
- If
address of the Lifetime specified in packet, then the Binding Update is nonzero and correspondent node uses a Routing
header to deliver the specified Care-of Address is not equal packet to the home mobile node through the care-of
address
for in the binding (as given recorded in the Home Address option in Binding Cache entry. Any ICMP
error message caused by the
packet), then this is a request packet on its way to cache a binding for the mobile node will
be returned normally to the correspondent node. Processing for this type of received Binding Update is
described in Section 8.3.
- If
On the Lifetime specified in other hand, if the correspondent node has no Binding Update is zero or the
specified Care-of Address matches the home address Cache
entry for the
binding, then this is a request mobile node, the packet will be routed to delete the mobile
node's
cached binding. Processing for this type of received Binding
Update is described in Section 8.4.
8.3. Requests to Cache a Binding
If a node receives a valid Binding Update requesting home link. There, it will be intercepted by the mobile node's
home agent, encapsulated, and tunneled to cache a
binding for a the mobile node, as specified in Section 8.2, then node's primary
care-of address. Any ICMP error message caused by the node
MUST examine packet on
its way to the Home Registration (H) bit mobile node while in the Binding Update
to determine how tunnel, will be returned to further process
the Binding Update. If mobile node's home agent (the source of the
Home Registration (H) bit is set, tunnel). By the Binding Update is processed
according
definition of IPv6 encapsulation [4], this encapsulating node MUST
relay certain ICMP error messages back to the procedure specified in Section 9.3.
If original sender of the Home Registration (H) bit
packet, which in this case is not set, then the receiving
node SHOULD create correspondent node.
Likewise, if a new entry in its Binding Cache packet for this a mobile node (or update its existing Binding Cache entry for this arrives at the mobile
node, if such an entry already exists). The home address of node's
previous default router (e.g., the mobile node is taken from the Home Address field in moved after the packet's Home
Address option. The new Binding Cache entry records packet
was sent), the association
between this home address router will encapsulate and tunnel the packet to the
mobile node's new care-of address for the binding, as
specified in either the Care-of Address field of the Binding Update
or in the Source Address field in the packet's IPv6 header. Any (if it has a Binding Cache entry created or updated
for the mobile node). As above, any ICMP error message caused by the
packet while in response to processing this
Binding Update MUST tunnel will be deleted after returned to the expiration previous default
router (the source of the Lifetime
period specified in tunnel), which MUST relay certain ICMP
error messages back to the Binding Update. correspondent node [4].
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8.4. Requests
Thus, in all cases, any meaningful ICMP error messages caused
by packets from a correspondent node to Delete a Binding mobile node will be
returned to the correspondent node. If a the correspondent node
receives a valid Binding Update requesting it persistent ICMP Destination Unreachable messages after
sending packets to delete a
cached binding for a mobile node, as specified in Section 8.2, then
the node MUST examine the Home Registration (H) bit based on an entry in the its Binding
Update to determine how to further process
Cache, the correspondent node SHOULD delete this Binding Update. Cache
entry. If the Home Registration (H) bit is set, the Binding Update is processed
according correspondent node subsequently transmits another
packet to the procedure specified in Section 9.4.
If mobile node, the Home Registration (H) bit is not set, then packet will be routed to the receiving node
MUST delete any existing entry in its Binding Cache for this mobile
node. The
node's home address of link, intercepted by the mobile node is taken from the Home
Address field in node's home agent, and
tunneled to the packet's Home Address option.
8.5. Sending Binding Acknowledgements
When any mobile node's primary care-of address using IPv6
encapsulation. The mobile node receives a packet containing will then return a Binding Update option
in which to
the Acknowledge (A) bit is set, correspondent node, allowing it SHOULD return to recreate a Binding
Acknowledgement option acknowledging receipt of the Binding Update.
If the node accepts the Binding Update and creates or updates an
entry in its (correct) Binding
Cache entry for this binding, the Status field in
the Binding Acknowledgement MUST be set mobile node.
8.9. Sending Packets to a value less than 128;
if Mobile Node
Before sending any packet, the sending node rejects the SHOULD examine its
Binding Update and does not create or
update an entry Cache for this binding, the Status field in the Binding
Acknowledgement MUST be set to a value greater than or equal to 128.
Specific values an entry for the Status field are described in Section 5.2 and
in the most recent "Assigned Numbers" [17].
As described in Section 5.2, destination address to which the
packet in which is being sent. If the sending node has a Binding
Acknowledgement is returned MUST include either an AH [7] or ESP [8]
header providing sender authentication, data integrity protection,
and replay protection; and Cache entry
for this address, the packet MUST be sent using sending node SHOULD use a Routing header in to
route the same way as any other packet sent to a this mobile node
using a care-of address (even if the binding was rejected), as
described in Section 8.9. The packet is routed first to (the destination node) by way
of the care-of address contained in the binding recorded in that Binding Update being acknowledged, and
then to the mobile node's home address. This Cache
entry. For example, assuming use of the a Type 0 Routing header ensures that the Binding Acknowledgement will be routed to [5], if
no other use of a Routing header is involved in the
current location routing of this
packet, the mobile node sending sets the Binding Update, whether fields in the
Binding Update was accepted or rejected.
8.6. Sending Binding Requests
Entries packet's IPv6 header
and Routing header as follows:
- The Destination Address in a the packet's IPv6 header is set to
the mobile node's care-of address copied from the Binding Cache MUST be deleted when their lifetime
expires. If such an entry
entry.
- The Routing header is still in active use in sending packets initialized to contain a single route
segment, with an Address of the mobile node, node's home address (the
original destination address to which the next packet sent to was being sent).
Following the mobile node definition of a Type 0 Routing header [5], this packet
will be routed normally, to the mobile node's home link, care-of address, where it will
be
intercepted and tunneled delivered to the mobile node. The node (the mobile node will
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then return a Binding Update to the sender, allowing it to create
a new Binding Cache entry for sending future packets to has associated the mobile
node. Communication
care-of address with its network interface). Normal processing of
the Routing header by the mobile node continues uninterrupted,
but the forwarding of this packet through the will then proceed as follows:
- The mobile node's home
agent creates additional overhead and latency node swaps the Destination Address in delivering packets
to the mobile node.
If packet's
IPv6 header and the sender knows that Address specified in the Binding Cache entry is still Routing header.
This results in active
use, it MAY send a Binding Request the packet's IP Destination Address being set to
the mobile node's home address.
- The mobile node in an attempt
to avoid this overhead and latency due to deleting and recreating then resubmits the Binding Cache entry. Since a Binding Request is a destination
option, it may, for example, be included in any packet already being
sent to its IPv6 module for
further processing, "looping back" the mobile node, such as a packet that is part of ongoing TCP
communication with inside the mobile
node. When Since the mobile node receives a
packet from some sender containing a Binding Request, it returns a
Binding Update to that sender, giving recognizes its own home address as
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one of its current binding and a new
lifetime.
8.7. Cache Replacement Policy
Any entry in a node's Binding Cache MUST be deleted after IP addresses, the
expiration of packet is processed further
within the Lifetime specified mobile node, in the Binding Update from which same way then as if the entry was created or mobile
node was last updated. Conceptually, a at home.
If, instead, the sending node
maintains a separate timer for each entry in its Binding Cache. When
creating or updating a has no Binding Cache entry in response for the
destination address to a received
and accepted Binding Update, which the packet is being sent, the sending
node sets simply sends the timer for this entry
to packet normally, with no Routing header. If
the specified Lifetime period. When destination node is not a Binding Cache entry's timer
expires, the mobile node deletes the entry.
Each node's Binding Cache will, by necessity, have (or is a finite size.
A mobile node MAY use any reasonable local policy for managing the space
within its Binding Cache, except that any entry marked as a "home
registration" (Section 9.3) MUST NOT be deleted from the cache until
is currently at home), the expiration of its lifetime period. When attempting to add a
new "home registration" entry in response packet will be delivered directly to this
node and processed normally by it. If, however, the destination node
is a Binding Update with mobile node that is currently away from home, the Home Registration (H) bit set, if insufficient space exists (or
can packet will
be reclaimed) in intercepted by the mobile node's Binding Cache, home agent and tunneled (using
IPv6 encapsulation [4]) to the mobile node's current primary care-of
address, as described in Section 9.6. The mobile node MUST reject
the Binding Update and SHOULD return will then send
a Binding Acknowledgement Update to the sending mobile node, as described in which Section 10.7,
allowing the Status field is set to 131
(insufficient resources). When otherwise attempting sending node to add create a new
entry to its Binding Cache, a node MAY, if needed, choose to drop any Cache entry already in for its Binding Cache, other than a "home registration"
entry, use
in order to make space for the new entry. For example, a
"least-recently used" (LRU) strategy for cache entry replacement
among entries not marked as a "home registration" is likely to work
well.
Any binding dropped from a node's Binding Cache due sending subsequent packets to lack of cache
space will be rediscovered and a new cache entry created, if the this mobile node.
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binding
9. Home Agent Operation
9.1. Receiving Router Advertisement Messages
For each link on which a router provides service as a home agent, the
router maintains a Home Agents List recording information about all
other home agents on that link. This list is still used in the dynamic
home agent address discovery mechanism, described in Section 9.2.
The information for the list is learned through receipt of the
periodic unsolicited multicast Router Advertisements from each other
home agent on the link, in which the Home Agent (H) bit is set, in a
manner similar to the Default Router List conceptual data structure
maintained by each host for Neighbor Discovery [13].
On receipt of a valid Router Advertisement, as defined in active use by the node
processing algorithm specified for sending packets. If Neighbor Discovery [13], the node sends a packet home
agent performs the following steps, in addition to a destination for which any steps already
required of it has dropped the
entry from its Binding Cache, by Neighbor Discovery:
- If the packet will be routed normally,
leading to Home Agent (H) bit in the mobile node's home link. There, Router Advertisement is not set,
skip all of the packet will be
intercepted following steps. There are no special processing
steps required by Mobile IP for this Router Advertisement, since
the mobile node's Advertisement was not sent by a home agent and tunneled to agent.
- Otherwise, extract the
mobile node's current primary care-of address. As when a Binding
Cache entry Source Address from the IP header of the
Router Advertisement. This is initially created, the link-local IP address on
this indirect routing to link of the mobile
node through its home agent will result in the mobile node sending
a Binding Update to this sending node when it receives Advertisement [13].
Determine the tunneled
packet, allowing global address of the router based on the
Prefix Information option received from it to add an entry again in which the Router
Address (R) bit is set (Section 6.2).
- Determine from the Router Advertisement the preference for this destination to its
Binding Cache.
8.8. Receiving ICMP Error Messages
When a correspondent node sends a packet to a mobile node, if
home agent. If the
correspondent node has Router Advertisement contains a Binding Cache entry for Home Agent
Information Option, then the preference is taken from the Home
Agent Preference field in the option; otherwise, the default
preference of 0 SHOULD be used.
- Determine from the destination
address of Router Advertisement the packet, then lifetime for
this home agent. If the correspondent node uses Router Advertisement contains a Routing
header to deliver the packet to Home
Agent Information Option, then the mobile node through lifetime is taken from
the care-of
address Home Agent Lifetime field in the binding recorded in option; otherwise, the Binding Cache entry. Any ICMP
error message caused
lifetime specified by the packet on its way to Router Lifetime field in the mobile node will Router
Advertisement SHOULD be returned normally to used.
- If the correspondent node.
On global address of the other hand, if home agent sending this
Advertisement, as determined above, is not already present in the correspondent node has no Binding Cache
entry
Home Agents List maintained by the receiving home agent, and the
lifetime for the mobile node, sending home agent, also as determined above,
is non-zero, create a new entry in the packet will be routed list, and initialize its
lifetime and preference to the mobile
node's values determined above.
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- If the global address of the home link, where it will be intercepted by agent sending this
Advertisement is already present in the mobile node's receiving home agent, encapsulated, agent's
Home Agents List, reset its lifetime and tunneled preference to the mobile node's primary
care-of address. Any ICMP error message caused by values
determined above.
- If the packet on
its way to address is already present in this home agent's Home
Agents List and the mobile node while received home agent lifetime value is zero,
immediately delete this entry in the Home Agents List.
A home agent SHOULD maintain an entry in the tunnel, will be returned to
the mobile node's its Home Agents List for
each such valid home agent (the source of the tunnel). By address until that entry's lifetime
expires, after which time the
definition of IPv6 encapsulation [4], this encapsulating entry MUST be deleted.
9.2. Dynamic Home Agent Address Discovery
When a node receives a Binding Update, it MUST
relay certain ICMP error messages back to validate it and
determine the original sender type of Binding Update according to the
packet, which steps described
in this case is Section 8.2. This section describes the correspondent node.
Likewise, if a packet for processing of a mobile node arrives at the mobile node's
previous default router (e.g., valid
Binding Update that indicates that the mobile node moved after the packet
was sent), the router will encapsulate and tunnel the packet to the
mobile node's new care-of address (if sending it has is
attempting dynamic home agent address discovery.
As described in Section 10.6, a Binding Cache entry
for the mobile node). As above, any ICMP error message caused node attempts dynamic home
agent address discovery by the
packet while in this tunnel will be returned sending its "home registration" Binding
Update to the previous default
router Home-Agents anycast address for its home IP subnet
prefix (the source of the tunnel), which packet MUST relay certain ICMP
error messages back to the correspondent node [4].
Thus, in all cases, any meaningful ICMP error messages caused
by packets from a correspondent node to also include a mobile node will be
returned to the correspondent node. If the correspondent node
receives persistent ICMP Destination Unreachable messages after
sending packets to Home Address option). A home
agent receiving such a mobile node based Binding Update that is serving this subnet
(the home agent is configured with this anycast address on an entry in one of its Binding
Cache,
network interfaces) MUST reject the correspondent node Binding Update and SHOULD delete this return
a Binding Cache
entry. If Acknowledgement indicating this rejection, with the Source
Address of the correspondent node subsequently transmits another
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of the mobile node, global unicast addresses of the packet will home agent. The Status field
in the Binding Acknowledgement MUST be routed set to the mobile
node's 135 (dynamic home link, intercepted by agent
address discovery response).
In this Binding Acknowledgement rejecting the mobile node's dynamic home agent, and
tunneled to the mobile node's primary care-of agent
address using IPv6
encapsulation. The mobile node will then return a discovery Binding Update to Update, this home agent SHOULD set the correspondent node, allowing it to recreate a (correct) Home
Agents List as follows:
- The Home Agents List in this Binding
Cache entry for the mobile node.
8.9. Sending Packets to a Mobile Node
Before sending any packet, the sending node Acknowledgement SHOULD examine its
Binding Cache for an entry for
contain the destination IP address to which of all home agents currently listed in
this home agent's own Home Agents List (Section 4.3). However,
if this home agent's own IP address would be placed in the
packet is being sent. If list
(as described below) as the first entry in the list, then this
home agent SHOULD NOT include its own address in the list in
the sending node has a Binding Cache entry
for Acknowledgement. Not placing this address, home agent's own
IP address in the sending list will cause the receiving mobile node SHOULD use a Routing header
to
route consider this home agent as the packet to most preferred home agent;
otherwise, this mobile node (the destination node) home agent will be considered to be preferred in
its order given by way
of its place in the care-of address list returned.
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- The IP addresses in the binding recorded Home Agents List should be placed in that
the Home Agents List in the Binding Cache
entry. For example, assuming use Acknowledgement in order
of decreasing preference value, based either on the respective
advertised preference from a Type Home Agent Information option or on
the default preference of 0 Routing header [5], if no other use of a Routing header preference is involved in advertised (or on
the routing of configured home agent preference for this
packet, the mobile node sets the fields in the packet's IPv6 header
and Routing header as follows:
- home agent itself).
The Destination Address in home agent with the packet's IPv6 header is set to highest preference SHOULD be listed
first, and the mobile node's care-of address copied from home agent with the Binding Cache
entry. lowest preference SHOULD be
listed last.
- The Routing header is initialized to contain a single route
segment, Among home agents with an Address of equal preference, their IP addresses in
the mobile node's home address (the
original destination address Home Agents List SHOULD be listed in an order randomized with
respect to which the packet was being sent).
Following the definition of other home agents with equal preference, each time
a Binding Acknowledgement with a Type 0 Routing header [5], non-empty Home Agents List is
returned by this packet
will home agent.
- The Option Length field in this Binding Acknowledgement
MUST be routed set to the mobile node's care-of address, 11 + 16 * N, where it will
be delivered to the mobile node (the mobile node has associated N is the
care-of address with its network interface). Normal processing number of IP
addresses included in the Routing header by Home Agents List field in the Binding
Acknowledgement.
The mobile node will node, upon receiving this Binding Acknowledgement, MAY
then proceed resend its Binding Update to the home agent address given as follows:
- The mobile node swaps the Destination
IP Source Address in of the packet's
IPv6 header and packet carrying the Address specified Binding Acknowledgement
or to any of the unicast IP addresses listed in the Routing header.
This results Home Agents List
field in the packet's IP Destination Address being set to Acknowledgement. For example, the mobile node's home address.
- The mobile node then resubmits the packet to may
re-attempt its IPv6 module home registration with each of these home agents in
turn, by sending each a Binding Update and waiting for
further processing. Since the mobile node recognizes matching
Binding Acknowledgement, until its own
home address as registration is accepted by one if its current IP addresses,
of these home agents. In trying each of the packet is
processed further within returned home agent
addresses, the mobile node, node SHOULD try each in the same way then as
if order listed in the mobile node was at home.
If, instead,
Home Agents List in the sending node has no Binding Cache entry for Acknowledgement. If the
destination address to which home agent
identified by the packet is being sent, Source Address field in the sending
node simply sends IP header of the packet normally, with no Routing header. If
carrying the destination node Binding Acknowledgement is not a mobile node (or is a mobile node that
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is currently at home), the packet will Home Agents
List, it SHOULD be delivered directly to this
node and processed normally by it. If, however, tried before the destination node
is a mobile node that is currently away from home, first address given in the packet will list;
otherwise, it SHOULD be intercepted by the mobile node's home agent and tunneled (using
IPv6 encapsulation [4]) to tried in the mobile node's current primary care-of
address, as described in Section 9.5. The mobile its listed order.
9.3. Primary Care-of Address Registration
When a node will then send receives a Binding Update, it MUST validate it and
determine the type of Binding Update according to the sending node, as steps described
in Section 10.5,
allowing 8.2. This section describes the sending node to create processing of a valid
Binding Cache entry for its use
in sending subsequent packets Update that requests the receiving node to this mobile node.
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9. Home Agent Operation
9.1. Receiving Router Advertisement Messages
For each link on which a router provides service serve as a its home
agent, registering its primary care-of address.
To begin processing the router maintains a Home Agents List recording the IP address of
all other home agents that link. This list is used in Binding Update, the dynamic home agent address discovery mechanism, described MUST perform
the following sequence of tests:
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The information for IPv6 4 August 1998
- If the list node is learned through receipt of periodic
unsolicited multicast Router Advertisements from each other not a router that implements home agent on
functionality, then the link, node MUST reject the Binding Update and
SHOULD return a Binding Acknowledgement to the mobile node, in
which the Home Agent (H) bit Status field is set, in a
manner similar set to 132 (home registration not
supported).
- Else, if the Default Router List conceptual data structure
maintained by each host home address for Neighbor Discovery [11].
On receipt of a valid Router Advertisement, as defined the binding (the Home Address field
in the
processing algorithm specified for Neighbor Discovery [11], packet's Home Address option) is not an on-link IPv6
address with respect to the home
agent extracts agent's current Prefix List,
then the Source Address of home agent MUST reject the packet Binding Update and performs SHOULD
return a Binding Acknowledgement to the
following steps, mobile node, in addition which the
Status field is set to any steps already required of it by
Neighbor Discovery: 133 (not home subnet).
- If Else, if the address Prefix Length field is not already present nonzero in the Binding Update
and this length differs from the length of the home agent's Home
Agents List, and own
knowledge of the advertisement's Router Lifetime is non-zero,
create a new entry in corresponding subnet prefix on the list, home link,
then the home agent MUST reject the Binding Update and initialize its lifetime from SHOULD
return a Binding Acknowledgement to the advertisement's Router Lifetime field.
- If mobile node, in which the address
Status field is already present in set to 136 (incorrect subnet prefix length).
- Else, if the home agent's Home Agents
List agent chooses to reject the Binding Update for
any other reason (e.g., insufficient resources to serve another
mobile node as a result of home agent), then the home agent SHOULD return a previously-received advertisement, reset
its lifetime
Binding Acknowledgement to the Router Lifetime value mobile node, in which the newly-received
advertisement.
- If the address Status
field is already present in set to an appropriate value to indicate the reason for
the rejection.
If the home agent's Home Agents
List and agent does not reject the received Router Lifetime value is zero, immediately
delete this entry in Binding Update as described
above, then it becomes the Home Agents List
A home agent SHOULD maintain an for the mobile node. The new
home agent (the receiving node) MUST then create a new entry in its Home Agents List
Binding Cache for
each this mobile node (or update its existing Binding
Cache entry for this mobile node, if such valid an entry already exists)
The home agent address until that entry's lifetime
expires, after which time the entry MUST be deleted.
9.2. Dynamic Home Agent Address Discovery
If a received Binding Update indicates that of the mobile node sending
it is attempting dynamic home agent address discovery, as described taken from the Home Address
field in Section 8.2, then the receiving node MUST process packet's Home Address option. The care-of address for
this Binding Cache entry is taken from the Care-of Address field of
the Binding Update as specified in this section.
A mobile node attempts dynamic home agent address discovery by
sending its "home registration" (if the Care-of Address Present (C) bit is set in
the Binding Update to Update) or from the Home-Agents
anycast address for its home IP subnet prefix (the packet MUST also
include a Home Source Address option, as described in Section 10.4). A home
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IPv6 13 March 1998 header (otherwise).
The home agent receiving such a MUST mark this Binding Update Cache entry as a "home
registration" to indicate that the node is serving this subnet
(the as a home
agent is configured with for this anycast address on one of its
network interfaces) MUST reject the binding. Binding Update and SHOULD return Cache entries marked as a Binding Acknowledgement indicating this rejection, with "home
registration" MUST be excluded from the Source
Address of normal cache replacement
policy used for the packet carrying Binding Cache (Section 8.7) and MUST NOT be
removed from the Binding Acknowledgement set to
one of Cache until the unicast addresses expiration of the home agent. Lifetime
period.
The Status field in lifetime for the Binding Acknowledgement Cache entry MUST NOT be set to 135 (dynamic home agent
address discovery response).
In this Binding Acknowledgement rejecting greater than the dynamic
remaining valid lifetime for the subnet prefix in the mobile node's
home agent address discovery specified with the Binding Update, Update. The remaining valid
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lifetime for this home agent SHOULD include prefix is determined by the
IP address of all other home agents currently listed in agent based on
its Home
Agents List. To include this list in the Binding Acknowledgement,
the Option Length field MUST be set to 11 + 16 * (the number own Prefix List entry for this prefix [13]. If the value of IP addresses included in the Other Home Agents
Lifetime field in specified by the
Binding Acknowledgement). The mobile node, upon receiving this
Binding Acknowledgement, MAY then resend node in its Binding Update to is
greater than this prefix lifetime, the unicast home agent address given as the IP Source Address of
the packet carrying MUST decrease the Binding Acknowledgement
binding lifetime to less than or equal to any of the
unicast IP addresses listed in prefix valid lifetime.
The home agent MAY further decrease the Other Home Agents field in specified lifetime for the Acknowledgement. For example,
binding, for example based on a local policy implemented by the mobile node may re-attempt
its home registration with each of these
agent. The resulting lifetime is stored by the home agents agent in turn, by
sending each a the
Binding Update Cache entry, and waiting for the matching this Binding
Acknowledgement, until its registration is accepted Cache entry MUST be deleted by one of these
the home agents.
9.3. Primary Care-of Address Registration
General processing agent after the expiration of a received this lifetime.
The Prefix Length in the Binding Update that requests a
binding to MUST also be cached, is described saved in Section 8.3. However, if the Home Registration (H)
Binding Cache entry.
If the Acknowledge (A) bit is set in the Binding Update, Update (it SHOULD
be), then
after following the step outlined for all home agent MUST return a Binding Acknowledgement to the
mobile node, constructed as follows:
- The Status field MUST be set to a value indicating success (the
value MUST be less than 128). The only currently defined success
Status value is 0, indicating simply that the Binding Update options was
accepted.
- The Sequence Number field MUST be copied from the Sequence Number
given in
Section 8.2, the receiving node Binding Update.
- The Lifetime field MUST process be set to the Binding Update remaining lifetime for
the binding as
specified set by the home agent in its "home registration"
Binding Cache entry for the mobile node. As described above,
this section rather lifetime MUST NOT be greater than following the general procedure remaining valid
lifetime for requests the subnet prefix in the mobile node's home address.
- The Refresh field MUST be set to cache a binding specified value less than or equal to
the Lifetime value being returned in Section 8.3.
To begin processing the Binding Update, Update. If the
home agent MUST perform stores the following sequence Binding Cache entry in nonvolatile storage
(that survives the crash or other failure of tests:
- If the node is not a router that implements home agent
functionality, agent),
then the node MUST reject the Binding Update and Refresh field SHOULD return a Binding Acknowledgement be set to the mobile node, in
which same value as the Status field is
Lifetime field; otherwise, the home agent MAY set the Refresh
field to 132 (home a value less than the Lifetime field, to indicate that
the mobile node SHOULD attempt to refresh its home registration not
supported).
- Else, if
at the indicated shorter interval (although the home address agent will
still retain the registration for the binding (the Home Address field
in Lifetime period, even if
the packet's Home Address option) is mobile node does not an on-link IPv6
address with respect refresh its registration within the
Refresh period).
In addition, the home agent MUST follow the procedure defined in
Section 9.5 to intercept packets on the mobile node's home agent's current Prefix List,
then link
addressed to the mobile node, while the home agent is serving as the
home agent MUST reject the Binding Update and SHOULD for this mobile node.
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return
9.4. Primary Care-of Address De-registration
When a node receives a Binding Acknowledgement to the mobile node, in which Update, it MUST validate it and
determine the
Status field is set type of Binding Update according to 133 (not home subnet).
- Else, if the Prefix Length field is nonzero steps described
in Section 8.2. This section describes the processing of a valid
Binding Update
and this length differs from the length of that requests the receiving node to no longer serve as
its home agent's own
knowledge of the corresponding subnet prefix on agent, de-registering its primary care-of address.
To begin processing the home link,
then Binding Update, the home agent MUST perform
the following test:
- If the receiving node has no entry in its Binding Cache for this
mobile node that is marked as a "home registration", then this
node MUST reject the Binding Update and SHOULD return a Binding
Acknowledgement to the mobile node, in which the Status field is
set to 136 (incorrect subnet prefix length).
- Else, if 137 (not home agent for this mobile node).
If the home agent chooses to does not reject the Binding Update for as described
above, then it MUST delete any other reason (e.g., insufficient resources to serve another existing entry in its Binding Cache
for this mobile node as a home agent), node.
If the Acknowledge (A) bit is set in the Binding Update (it SHOULD
be), then the home agent SHOULD MUST return a Binding Acknowledgement to the
mobile node, in which the constructed as follows:
- The Status field is MUST be set to an appropriate a value to indicate the reason for
the rejection.
If the home agent does not reject indicating success (the
value MUST be less than 128). The only currently defined success
Status value is 0, indicating simply that the Binding Update as described
above, then it becomes the home agent for the mobile node. was
accepted.
- The new
home agent (the receiving node) Sequence Number field MUST then create a new entry or
update the existing entry in its Binding Cache for this mobile node's
home address (given in be copied from the Home Address option Sequence Number
given in the packet), as
described in Section 8.3. Binding Update.
- The Lifetime field MUST be set to zero.
- The Refresh field MUST be set to zero.
In addition, the home agent MUST mark
this Binding Cache entry as a "home registration" stop intercepting packets on the
mobile node's home link addressed to indicate that the mobile node (Section 9.5).
9.5. Intercepting Packets for a Mobile Node
While a node is serving as a the home agent for this binding. mobile node (while the
node has an entry in its Binding Cache entries for this mobile node that is
marked as a "home registration" registration"), this node MUST be excluded from attempt to intercept
packets on the normal cache replacement policy used for mobile node's home link addressed to the Binding Cache
(Section 8.7) mobile node,
and MUST NOT be removed from the Binding Cache until
the expiration of tunnel each intercepted packet to the Lifetime period.
If mobile node using
using IPv6 encapsulation [4].
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In order to intercept such packets on the home agent was not already serving as link, when a node
becomes the home agent for this some mobile node (the home agent (it did not already
have a Binding Cache entry for this home address mobile node marked as a "home
registration"), then the home agent MUST multicast onto the home link
a "gratuitous" Neighbor Advertisement message [11] on behalf of the mobile node, in
order to begin intercepting packets addressed to it while it is away
from home. message [13] on behalf of the
mobile node. Specifically, the home agent follows performs the following
steps:
- The home agent examines the value of the Prefix Length field
in the new "home registration" Binding Update. Cache entry. If this
value is zero, the following step is carried out only for the
individual home address specified
(in the Home Address option in the packet) for this binding. If, instead,
this field is nonzero, then the following step is carried out
for each address for the mobile node formed from the interface
identifier in the mobile node's home address in this Binding Update binding
(the remaining low-order bits in the address after the indicated
subnet prefix), together with each one of the subnet prefixes
currently considered by the home agent to be on-link (including
both the link-local and site-local prefix).
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- For each specific IP address for the mobile node determined
in the first step above, the home agent multicast multicasts onto the
home link (to the all-nodes multicast address) a Neighbor
Advertisement message [11] [13] on behalf of the mobile node, to
advertise the home agent's own link-layer address for this IP
address. The Target Address in the Neighbor Advertisement
message MUST be set to this IP address for the mobile node, and
the Advertisement MUST include a Target Link-layer Address option
specifying the home agent's link-layer address. The Solicited
Flag (S) in the Advertisement MUST NOT be set, since it was not
solicited by any Neighbor Solicitation message. The Override
Flag (O) in the Advertisement MUST be set, indicating that the
Advertisement SHOULD override any existing Neighbor Cache entry
at any node receiving it.
Any node on the home link receiving one of the Neighbor Advertisement
messages described above will thus update its Neighbor Cache to
associate the mobile node's address with the home agent's link
layer address, causing it to transmit any future packets for the
mobile node normally destined to this address instead to the mobile
node's home agent. Since multicasts on the local link (such as
Ethernet) are typically not guaranteed to be reliable, the home
agent MAY retransmit this Neighbor Advertisement message up to
MAX_ADVERT_REXMIT times to increase its reliability. It is still
possible that some nodes on the home link will not receive any of
these Neighbor Advertisements, but these nodes will eventually be
able to detect the link-layer address change for the mobile node's
home address, through use of Neighbor Unreachability Detection [11].
In addition, while this [13].
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While a node is serving as a home agent for this some mobile node (it
still has a "home registration" entry for this mobile node in its
Binding Cache), it the home agent uses IPv6 Neighbor Discovery [13]
to intercept unicast packets on the home link addressed the mobile
node's home address. In order to intercept packets in this way,
the home agent MUST act as a proxy for this mobile node to reply to
any received Neighbor Solicitation messages for it. When a home
agent receives a Neighbor Solicitation message, it MUST check if the
Target Address specified in the message matches the home address
of any mobile node for which it has a Binding Cache entry marked
as a "home registration". This check MUST include all possible
home addresses for the mobile node, based on the subnet prefixes
currently considered to be on-link by the home agent (including the
corresponding link-local address and site-local address), if the
Prefix Length field was nonzero in the Binding Cache entry for this mobile node (from
the Binding Update that created this "home registration" binding at the home
agent. Cache entry) is nonzero.
If such an entry exists in the home agent's Binding Cache, the home
agent MUST reply to the Neighbor Solicitation message
with a Neighbor Advertisement message, giving Neighbor Solicitation message with a Neighbor
Advertisement message, giving the home agent's own link-layer address
as the link-layer address for the specified Target Address. Acting
as a proxy in this way allows other nodes on the mobile node's home
link to resolve the mobile node's IPv6 home address, and allows
the home agent to to defend these addresses on the home link for
Duplicate Address Detection [13].
9.6. Tunneling Intercepted Packets to a Mobile Node
For any packet sent to a mobile node from the mobile node's home
agent (for which the home agent is the original sender of the
packet), the home agent is operating as a correspondent node of
the mobile node for this packet and the procedures described in
Section 8.9 apply. The home agent (as a correspondent node) uses a
Routing header to route the packet to the home agent's own
link-layer address as mobile node by way of the link-layer
care-of address for in the specified
Target Address. Acting as a proxy home agent's Binding Cache (the mobile node's
primary care-of address, in this way allows other nodes on case).
While the mobile node's node is away from home link to resolve and this node is acting
as the mobile node's IPv6 home
address, and allows agent, the home agent to to defend these addresses intercepts any
packets on the home link for Duplicate Address Detection [11].
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Any packet addressed to the mobile node's home address
(including addresses formed from other on-link prefixes, if the
Prefix Length field was nonzero in the Binding Update) will thus be received by Update), as described
in Section 9.5. The home agent cannot use a Routing header to
forward these intercepted packets to the mobile node's node, since it cannot
modify the packet in flight without invalidating any existing IPv6
AH [8] or ESP [9] header present in the packet.
For forwarding each intercepted packet to the mobile node, the
home agent while MUST tunnel the packet to the mobile node using IPv6
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encapsulation [4]; the tunnel entry point node is the home agent,
and the tunnel exit point node is the primary care-of address as
registered away
from home. For any such with the home agent (which is an address of the mobile
node itself). When a home agent encapsulates an intercepted packet received by
for forwarding to the mobile node, the home agent sets the Source
Address in the prepended tunnel IP header to the home agent for agent's own IP
address, and sets the
mobile node, Destination Address in the home agent SHOULD tunnel the packet IP header
to the mobile node's primary care-of address. When received by the
mobile node at (using its primary care-of address, as described address), normal processing of
the tunnel header [4] will result in Section 9.5. decapsulation and processing of
the original packet by the mobile node.
However, packets addressed to the mobile node's link-local address
MUST NOT be tunneled to the mobile node. Instead, such a packet MUST
be discarded, and the home agent SHOULD return an ICMP Destination
Unreachable, Code 3, message to the packet's Source Address (unless
this Source Address is a multicast address).
Similarly, packets Packets addressed to
the mobile node's site-local address
MUST NOT SHOULD be tunneled to the mobile node, unless
node by default, but this behavior MUST be configurable to disable
it; currently, the exact definition and semantics of a "site" and a
site-local address are undefined in IPv6, and this default behavior
might change at some point in the future.
Tunneling of multicast packets to a mobile node follows similar
limitations to those defined above for unicast packets addressed to
the mobile node's
registered primary care-of link-local and site-local addresses. Multicast
packets addressed to a multicast address is within with link-local scope [7],
to which the same site as mobile node is subscribed, MUST NOT be tunneled
to the mobile node's home address. For any node; such packet not forwarded packets SHOULD be silently discarded
(after delivering to other local multicast recipients). Multicast
packets addressed to a multicast address with scope larger
than link-local but smaller than global (e.g., site-local and
organization-local) [7], to which the mobile node is subscribed,
SHOULD be tunneled to the mobile node by default, but this behavior
MUST be configurable to disable it; this default behavior might
change at some point in the future as the definition of these scopes
become better defined in IPv6.
9.7. Renumbering the Home Subnet
IPv6 provides mechanisms through Neighbor Discovery [13] and Address
Autoconfiguration [22] to aid in renumbering a subnet, such as when a
site switches to a new network service provider. In renumbering, new
prefixes and addresses can be introduced for this reason, the packet MUST subnet and old ones
can be discarded, deprecated and the
home agent SHOULD return an ICMP Destination Unreachable, Code 3,
message removed. These mechanisms are defined to work
while all nodes using the packet's Source Address (unless this Source Address is
a multicast address). Currently, however, the exact definition and
semantics of a "site" old prefixes are undefined in IPv6, and the mechanism for
a home agent at home, connected to determine if the care-of address is within
link using these prefixes. Mobile IPv6 extends these mechanisms for
the same
site as case in which one or more mobile nodes using the old prefixes are
away from home address is outside while the scope of this document.
9.4. Primary Care-of Address De-registration
General processing of a received Binding Update that requests a
binding to be deleted, is described renumbering takes place.
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The IPv6 renumbering mechanisms are based on nodes on the Home Registration (H) bit is set link
receiving Prefix Information options in Router Advertisement messages
giving the Binding Update, then
after following the step outlined valid lifetime and preferred lifetime for all Binding Update options in
Section 8.2, different
prefixes on the receiving node MUST process link [13]. Mobile IPv6 arranges to tunnel certain
Router Advertisements giving "important" Prefix Information options
to mobile nodes while away from home. To avoid the Binding Update as
specified in this section rather than following need to tunnel
all Router Advertisements from the general procedure
for requests home link to delete a cache binding specified in Section 8.4. mobile node away
from home, those Router Advertisements that are tunneled to the
mobile node are retransmitted until acknowledged. To begin processing avoid possible
security attacks from forged Router Advertisements tunneled to
the Binding Update, mobile node, all such tunneled Router Advertisements must be
authenticated to the mobile node by its home agent MUST perform using AH [8] or
ESP [9].
Specifically, a home agent serving some mobile node SHOULD construct
and tunnel to the following sequence mobile node a new Router Advertisement when any of tests:
the following conditions occur:
- If The preferred or valid lifetime for an existing prefix on the node
home link is not reduced.
- A new prefix is introduced on the home link.
- The state of the home agent's AdvManagedFlag flag [13] changes
from FALSE to TRUE or from TRUE to FALSE.
The home agent determines these conditions based on its own
configuration as a router and based on the Router Advertisements
that implements it receives on the home link. The home agent
functionality, then constructs a new
Router Advertisement message containing no options other than the node MUST reject
Prefix Information options describing the Binding Update prefixes for which one of
the conditions above has occurred since the last Router Advertisement
tunneled to and acknowledged by the mobile node. When multiple
conditions occur at or near the same time, the home agent SHOULD return
attempt to combine them into a Binding Acknowledgement single Router Advertisement message to
the mobile node, in
which the Status field is set node.
In tunneling each such Router Advertisement to 132 (home registration not
supported).
- Else, if the mobile node, the
home address for agent MUST construct the binding (the Home packet as follows:
- The Source Address
field in the packet's Home Address option) is not an on-link IPv6 address with respect header MUST be set to the
home agent's current Prefix
List, then it IP address to which the mobile node addressed its
current home registration.
- The packet MUST reject the Binding Update include either an AH [8] or ESP [9] header
providing sender authentication, data integrity protection, and SHOULD return
replay protection.
- The packet MUST include a Binding Request destination option.
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Binding Acknowledgement
- The packet MUST be tunneled to the mobile node, node's primary care-of
address using a Routing header, in which the Status
field is set to 133 (not home subnet).
If the home agent does not reject the Binding Update same way as described
above, then it MUST delete any existing entry in its Binding Cache
for this mobile node.
9.5. Tunneling Intercepted Packets to a Mobile Node
For any packet
sent to a the mobile node from originated by the mobile node's home agent (for which (rather than
using IPv6 encapsulation, as would be used by the home agent is the original sender of the
packet), the for
intercepted packets).
The home agent SHOULD periodically continue to retransmit this
tunneled packet to the mobile node, until it is operating as a correspondent acknowledged by the
receipt from the mobile node of a Binding Update matching the Binding
Request in the packet (i.e., with matching Sequence Number). If
while the mobile node for this packet and is still retransmitting a Router Advertisement
to the procedures mobile node, another condition as described in
Section 8.9 apply. The above occurs on
the home agent (as a correspondent node) uses a
Routing header link causing another Router Advertisement to route the packet be tunneled to
the mobile node by way of node, the home agent SHOULD combine any Prefix Information
options in the unacknowledged Router Advertisement into the new
Router Advertisement and then begin retransmitting the new Router
Advertisement rather than the
care-of address old one.
In addition, as described in Section 9.3, the home agent's Binding Cache (the lifetime returned by a
mobile node's home agent in its Binding Acknowledgement in response
to registration of a new primary care-of address, in this case).
In addition, while address by the mobile node is away from home and this node is
acting as the mobile node's home agent,
MUST be no greater than the home agent intercepts any
packets on remaining valid lifetime for the home link addressed to subnet
prefix in the mobile node's home address, address. Furthermore, as described
in Section 9.3. The home agent cannot use a Routing
header to forward these intercepted packets to 10.7, Binding Updates sent by the mobile node,
since it cannot modify the packet in flight without invalidating any
existing IPv6 Authentication header present in the packet [7].
For forwarding each intercepted packet node to other
nodes MUST use a lifetime no greater than the remaining lifetime of
its home registration of its primary care-of address. These limits
on a binding lifetimes ensure that no node uses a mobile node, the node's home agent MUST tunnel the packet to
address beyond the time that it becomes invalid. The mobile node using IPv6
encapsulation [4];
SHOULD further limit the tunnel entry point node is lifetimes that it sends on any Binding
Updates to be within the remaining preferred lifetime for the prefix
in its home agent, address.
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10. Mobile Node Operation
10.1. Sending Packets While Away from Home
While a mobile node itself (using is away from home, it continues to use its
primary home
address as well as also using one or more care-of address as registered with the home agent). addresses. When
sending a
home agent encapsulates an intercepted packet for forwarding to the while away from home, a mobile node, the home agent sets the Source Address node MAY choose among
these in selecting the prepended
tunnel IP header to address that it will use as the home agent's own IP address, and sets source of the
Destination Address in
packet, as follows:
- From the tunnel point of view of protocol layers and applications
above Mobile IP header to the mobile node's
primary care-of address. When received by (e.g., transport protocols), the mobile node (using
will generally use its
primary care-of address), normal processing of home address as the tunnel header [4]
will result in decapsulation and processing source of the original packet by
for most packets, even while away from home, since Mobile IP
is designed to make mobility transparent to such software.
Doing so also makes the mobile node.
9.6. Renumbering node's mobility and the Home Subnet
Neighbor Discovery [11] specifies a mechanism by which all nodes on a
subnet can gracefully autoconfigure new addresses, say by each node
combining a new subnet prefix with its existing link-layer address.
As fact that it is
currently specified, this mechanism works when away from home transparent to the correspondent nodes are on
the same link as the router issuing the necessary multicast
with which it communicates. For packets
to advertise the new subnet prefix(es) appropriate for sent that are part of
transport-level connections established while the link.
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However, for mobile nodes away from node
was at home, special care must be taken
to allow the mobile nodes to renumber gracefully. The most direct
method of ensuring node MUST use its home address in this is
way. Likewise, for the home agent to encapsulate and
tunnel the multicast packets to the primary care-of address sent that are part of each transport-level
connections that the mobile node for which it is serving as may still be using after moving
to a new location, the home agent. The rules for
this are as follows:
- A mobile node assumes that its subnet prefix has not changed
unless it receives an authenticated Router Advertisement message
from SHOULD use its home agent that the prefix has changed.
- address
in this way. When sending such packets, Mobile IP will modify
the mobile node is at home, packet to move the home agent does not tunnel
Router Advertisements address into a Home Address option
and will set the IPv6 header's Source Address field to it.
- The one of
the mobile node's home agent serves as a proxy for care-of addresses; these modifications to
the packet are then reversed in the node receiving the packet,
restoring the mobile node's home address to be the packet's
Source Address before processing by higher protocol layers and link-local address, including defending
these addresses
applications.
- For short-term communication, particularly for Duplicate Address Detection, while communication that
may easily be retried if it fails, the mobile node is registered with MAY choose
to directly use one of its care-of addresses as the home agent away from home.
- When source of
the packet, thus not requiring the use of a home subnet prefix changes, Home Address option
in the packet. An example of this type of communication might
be DNS queries sent by the home agent tunnels Router
Advertisement packets to each mobile node registered with it that
is currently away from home and using [11, 12]. Using the
mobile node's care-of address as the source for such queries will
generally have a lower overhead than using the mobile node's
home address with address, since no extra options need be used in either the
affected subnet prefix. Such tunneled Router Advertisements MUST
query or its reply, and all packets can be authenticated [7].
- When a routed normally,
directly between their source and destination without relying
on Mobile IP. If the mobile node receives a tunneled Router Advertisement
containing a new subnet prefix, it MUST perform has no particular knowledge
that the communication being sent fits within this general type
of communication, however, the standard
autoconfiguration operation to create its new address.
- When a mobile node returns to SHOULD NOT use its home link, it must again
perform Duplicate Address Detection at
care-of address as the source of the packet in this way.
If the earliest possible
moment after it has deleted its "home registration" binding with
its home agent.
- A mobile node MAY send a Router Solicitation to uses one of its home agent at
any time, within care-of addresses as the constraints imposed by rate control defined
by Neighbor Discovery [11]. source
of some packet while away from home, no special Mobile IP processing
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10. Mobile Node Operation
10.1. Sending Packets While Away from Home
While a mobile node
is away from home, it continues required for sending this packet. The packet is simply addressed
and transmitted in the same way as any normal IPv6 packet, setting
the Source Address field in the packet's IPv6 header to use its home
address as well as also using one or more this care-of addresses. When
sending a packet
address.
On the other hand, if while away from home, a the mobile node MAY choose among
these in selecting the uses its
home address that it will use as the source of the
packet, as follows:
- From a packet from the point of view of
higher protocol layers and or applications
above as described above, special
Mobile IP (e.g., transport protocols), the mobile node
will generally use its home address as the source processing of the this packet is required for most packets, even while away from home, since the insertion of
the Home Address option. Specifically:
- Since Mobile IP is designed to make mobility transparent to such software.
Doing so also makes the node's mobility and higher protocol layers (e.g.,
to TCP), the fact that it packet is
currently away from initially constructed using the mobile
node's home transparent to address as the correspondent nodes
with which it communicates. For packets sent that are part of
transport-level connections established while packet's Source Address, in the same
way as if the mobile node
was were at home, home.
- If the mobile node MUST use its home address in this
way. Likewise, is at home, no special Mobile IP processing
for packets this packet is required. The packet is sent that normally and the
following additional steps are part of transport-level
connections that not performed.
- Likewise, if the mobile node may still be using after moving
to a new location, Source Address field in the packet's IPv6 header
is not the mobile node SHOULD use its node's home address
in this way. When sending such packets, address, no special Mobile IP will modify
the
processing for this packet to move is required. The packet is sent
normally and the home address into following additional steps are not performed.
- Otherwise, insert a Home Address option
and will set into the packet, with the
Home Address field copied from the original value of the Source
Address field in the packet.
- Change the IPv6 header's Source Address field in the packet's IPv6 header to
one of the mobile node's care-of address; these modifications to the packet
are then reversed in the node receiving the packet, restoring addresses. This will typically
be the mobile node's home address to current primary care-of address, but MUST
be the packet's Source Address
before processing by higher protocols layers and applications.
- For short-term communication, particularly for communication a care-of address with a subnet prefix that
may easily be retried if it fails, is on-link on the
network interface on which the mobile node MAY choose to
directly use one of its care-of addresses as will transmit the source
packet.
This addition of the
packet, thus not requiring the use of a Home Address option in
the packet. An example of this type of communication might be
DNS queries sent by the mobile node [9, 10]. Using the mobile
node's care-of address as the source for such queries will
generally have to a lower overhead than using the mobile node's
home address, since no extra options need packet MUST be used in either
performed before outgoing IPsec processing, such as the
query addition of
an AH [8] or its reply, and all packets can be routed normally,
directly between their source and destination without relying
on Mobile IP. If ESP [9] header to the mobile node has no particular knowledge
that packet, is performed. Likewise,
IPsec processing for a received packet containing a Home Address
option MUST be performed before the communication being sent fits within this type packet is possibly modified as
part of
communication, however, processing the Home Address option. By using the mobile node SHOULD NOT use its care-of
address as the source of the packet Source Address in this way.
If the IPv6 header, with the mobile node uses one of its care-of addresses as
node's home address instead in the Home Address option, the source
of some packet while away from home, no special Mobile IP processing
is required for sending this packet. The packet is simply addressed
will be able to safely pass through any router implementing ingress
filtering [6].
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and transmitted
10.2. Receiving Packets While Away from Home
While away from home, a mobile node will receive packets addressed to
its home address, by one of three methods:
- Packets sent by a correspondent node that does not have a
Binding Cache entry for the mobile node, will be sent by the
correspondent node in the same way as any normal IPv6 packet, setting
the Source Address field in IP packet. Such
packets will then be intercepted by the packet's mobile node's home agent,
encapsulated using IPv6 header encapsulation [4], and tunneled to this the
mobile node's primary care-of address.
On
- Packets sent by a correspondent node that has a Binding Cache
entry for the mobile node that contains the mobile node's current
care-of address, will be sent by the correspondent node using
a Routing header. The packet will be addressed to the mobile
node's care-of address, with the final hop in the other hand, if while away from home, Routing header
directing the packet to the mobile node uses its node's home address as the source of a packet from address; the point of view of
higher protocol layers or applications as described above, special
Mobile IP
processing of this packet is required for the insertion last hop of the Home Address option. Specifically:
- Since Mobile IP Routing header is transparent to higher protocol layers (e.g., entirely
internal to TCP), the packet is initially constructed using the mobile
node's node, since the care-of address and home
address as are both addresses within the packet's Source Address, in mobile node.
- Packets sent by a correspondent node that has a Binding Cache
entry for the same
way as if mobile node that contains an out-of-date care-of
address for the mobile node, will be sent by the correspondent
node were at home.
- using a Routing header, as described above. If the mobile
node is at home, no special Mobile IP processing
for this packet is required. The packet is sent normally a Binding Update to its previous default router when
moving from this care-of address to another, and the
following additional steps are not performed.
- Likewise, if the Source Address field Binding
Cache entry that was created from this Binding Update is still
present in the packet's this router's Binding Cache, then such a packet
will be intercepted by this router, encapsulated using IPv6 header
is not
encapsulation [4], and tunneled to the mobile node's home address, no special Mobile IP
processing for primary
care-of address (registered with this packet is required. The packet is sent
normally and the following additional steps are not performed.
- Otherwise, insert a Home Address option into router, acting as a home
agent for this out-of-date care-of address).
For packets received by either the packet, with first or last of these three
methods, the
Home Address field copied from mobile node SHOULD send a Binding Update to the original value
sender of the Source
Address field packet, as described in Section 10.7, subject to the packet.
- Change
rate limiting defined in Section 10.10. The mobile node SHOULD
also process the Source Address field received packet in the packet's manner defined for IPv6 header to
one of
encapsulation [4], which will result in the encapsulated (inner)
packet being processed normally by upper-layer protocols within the
mobile node's care-of addresses. This will typically
be node, as if it had been addressed (only) to the mobile node's current primary care-of address, but MUST
be a care-of address with a subnet prefix that is on-link on
home address.
For packets received by the
network interface on which second method above (using a Routing
header), the mobile node will transmit the
packet.
This addition of SHOULD process the Home Address option to a received packet MUST be
performed before outgoing IPsec processing, such as in the addition
manner defined for the type of
an AH [7] or ESP [8] IPv6 Routing header used [5], which
will result in the packet being processed normally by upper-layer
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protocols within the mobile node, as if it had been addressed (only)
to the packet, is performed. Likewise,
IPsec processing mobile node's home address.
In addition, the general procedures defined by IPv6 for Routing
headers suggest that a received packet containing a Home Address
option MUST Routing header MAY be performed before automatically
"reversed" to construct a Routing header for use in any response
packets sent by upper-layer protocols, if the received packet is possibly modified as
part of processing the Home Address option. By using
authenticated [5]. If this is done for upper-layer protocol response
packets sent by a mobile node while away from home, the mobile
node SHOULD NOT include its own care-of
address as address, which appears in
the Source Address Routing header of the received packet, in the IPv6 header, with reversed route
for the response packet. If the received Routing header contained
no additional hops (other than the mobile node's home address instead in the Home Address option, the packet
will be able to safely pass through any router implementing ingress
filtering [6].
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10.2.
care-of address), then any upper-layer protocol response packet
SHOULD NOT include a Routing header.
10.3. Movement Detection
A mobile node MAY use any combination of mechanisms available to it
to detect when it has moved from one link to another. The primary
movement detection mechanism for Mobile IPv6 defined here uses the
facilities of IPv6 Neighbor Discovery, including Router Discovery and
Neighbor Unreachability Detection. The description here is based on
the conceptual model of the organization and data structures defined
by Neighbor Discovery [11]. [13].
Mobile nodes SHOULD use Router Discovery to discover new routers and
on-link subnet prefixes; a mobile node MAY send Router Solicitation
messages, or MAY wait for unsolicited (periodic) multicast Router
Advertisement messages, as specified for Router Discovery [11]. [13].
Based on received Router Advertisement messages, a mobile node (in
the same way as any other node) maintains an entry in its Default
Router List for each router, and an entry in its Prefix List for each
subnet prefix, that it currently considers to be on-link. Each entry
in these lists has an associated invalidation timer value (extracted
from the Router Advertisement) used to expire the entry when it
becomes invalid.
While away from home, a mobile node SHOULD select one router from
its Default Router List to use as its default router, and one subnet
prefix advertised by that router from its Prefix List to use as
the subnet prefix in its primary care-of address. A mobile node
MAY also have associated additional care-of addresses, using other
subnet prefixes from its Prefix List. The method by which a mobile
node selects and forms a care-of address from the available subnet
prefixes is described in Section 10.3. 10.4. The mobile node registers
its primary care-of address with its home agent, as described in
Section 10.4. 10.5.
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While a mobile node is away from home and using some router as its
default router, it is important for the mobile node to be able to
quickly detect when that router becomes unreachable, so that it can
switch to a new default router and to a new primary care-of address.
Since some links (notably wireless) do not necessarily work equally
well in both directions, it is likewise important for the mobile
node to detect when it becomes unreachable to packets sent from its
default router, so that the mobile node can take steps to ensure that
any correspondent nodes attempting to communicate with it can still
reach it through some other route.
To detect when its default router becomes unreachable, a mobile
node SHOULD use Neighbor Unreachability Detection. As specified in
Neighbor Discovery [11], [13], while the mobile node is actively sending
packets to (or through) its default router, the mobile node can
detect that the router (as its neighbor) is still reachable either
through indications from upper layer protocols on the mobile node
that a connection is making "forward progress" (e.g., receipt of TCP
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acknowledgements for new data transmitted), or through receipt of a
Neighbor Advertisement message from its default router in response
to an explicit Neighbor Solicitation messages to it. Note that
although this mechanism only detects that the mobile node's default router
has become unreachable to the mobile node only while the mobile node
is actively sending packets to it, this is the only time that this
direction of reachability confirmation is needed. Confirmation
that the mobile node is still reachable from the router is handled
separately, as described below.
For a mobile node to detect when it has become unreachable to from its
default router, however, the mobile node cannot efficiently rely on Neighbor
Unreachability Detection alone, since the network overhead would be
prohibitively high in many cases for a mobile node to continually
probe its default router with Neighbor Solicitation messages even
when it is not otherwise actively sending packets to it. Instead,
a mobile node SHOULD consider receipt of any IPv6 packets from its
current default router as an indication that it is still reachable
from the router. Both packets from the router's IP address and
(IPv6) packets from its link-layer address (e.g., those forwarded but
not originated by the router) SHOULD be considered.
Since the router SHOULD be sending periodic unsolicited multicast
Router Advertisement messages, the mobile node will have frequent
opportunity to check if it is still reachable from its default
router, even in the absence of other packets to it from the router.
If Router Advertisements that the mobile node receives include
an Advertisement Interval option, the mobile node MAY use its
Advertisement Interval field as an indication of the frequency with
which it should expect to continue to receive future Advertisements
from that router. This field specifies the minimum rate (the maximum
amount of time between successive Advertisements) that the mobile
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node should expect. If this amount of time elapses without the
mobile node receiving any Advertisement from this router, the mobile
node can be sure that at least one Advertisement sent by the router
has been lost. It is thus possible for the mobile node to implement
its own policy for determining the number of Advertisements from
its current default router it is willing to tolerate losing before
deciding to switch to a different router from which it may currently
be correctly receiving Advertisements.
On some types of network interfaces, the mobile node MAY also
supplement this monitoring of Router Advertisements, by setting its
network interface into "promiscuous" receive mode, so that it is able
to receive all packets on the link, including those not link-level
addressed to it. it (i.e., disabling link-level address filtering). The
mobile node will then be able to detect any packets sent by the
router, in order to to detect reachability from the router. This
use of promiscuous mode may be useful on very low bandwidth (e.g.,
wireless) links, but its use MUST be configurable on the mobile node.
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If the above means do not provide indication that the mobile node is
still reachable from its current default router (i.e., the mobile
node receives no packets from the router for a period of time), then
the mobile node SHOULD attempt to actively probe the router with
Neighbor Solicitation messages, even if it is not otherwise actively
sending packets to the router. If it receives a solicited Neighbor
Advertisement message in response from the router, then the mobile
node can deduce that it is still reachable. It is expected that the
mobile node will in most cases be able to determine its reachability
from the router by listening for packets from the router as described
above, and thus, such extra Neighbor Solicitation probes should
rarely be necessary.
With some types of networks, it is possible that additional
indications about link-layer mobility can be obtained from
lower-layer protocol or device driver software within the mobile
node. However, a mobile node MUST NOT assume that all link-layer
mobility indications from lower layers indicate a movement of the
mobile node to a new link, such that the mobile node would need to
switch to a new default router and primary care-of address. For
example, movement of a mobile node from one cell to another in many
wireless LANs can be made transparent to the IP level through use of
a link-layer "roaming" protocol, as long as the different wireless
LAN cells all operate as part of the same IP link with the same
subnet prefix. Upon lower-layer indication of link-layer mobility,
the mobile node MAY send Router Solicitation messages to determine if
new routers (and new on-link subnet prefixes) are present on its new
link.
Such lower-layer information might also be useful to a mobile node in
deciding to switch its primary care-of address to one of the other
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care-of addresses it has formed from the on-link subnet prefixes
currently available through different routers from which the mobile
node is reachable. For example, a mobile node MAY use signal
strength or signal quality information (with suitable hysteresis) for
its link with the available routers to decide when to switch to a new
primary care-of address using that router rather than its current
default router (and current primary care-of address). Even though
the mobile node's current default router may still be reachable in
terms of Neighbor Unreachability Detection, the mobile node MAY use
such lower-layer information to determine that switching to a new
default router would provide a better connection.
10.3.
10.4. Forming New Care-of Addresses
After detecting that it has moved from one link to another (i.e., its
current default router has become unreachable and it has discovered a
new default router), a mobile node SHOULD form a new primary care-of
address using one of the on-link subnet prefixes advertised by the
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address using one of the on-link subnet prefixes advertised by the
new router. A mobile node MAY form a new primary care-of address
at any time, except that it MUST NOT do so too frequently (not more
often than once per MAX_UPDATE_RATE seconds).
In addition, after discovering a new on-link subnet prefix, a mobile
node MAY form a new (non-primary) care-of address using that subnet
prefix, even when it has not switched to a new default router. A
mobile node can have only one primary care-of address at a time
(which is registered with its home agent), but it MAY have an
additional care-of address for any or all of the subnet prefixes on its
current link. Furthermore, since a wireless network interface may
actually allow a mobile node to be reachable on more than one link at
a time (i.e., within wireless transmitter range of routers on more
than one separate link), a mobile node MAY have care-of addresses
on more than one link at a time. The use of more than one care-of
address at a time is described in Section 10.12. 10.15.
As described in Section 4, in order to form a new care-of address,
a mobile node MAY use either stateless [18] [22] or stateful (e.g.,
DHCPv6 [2]) address autoconfiguration. If a mobile node needs to
send packets as part of the method of address autoconfiguration,
it MUST use an IPv6 link-local address rather than its own IPv6
home address as the Source Address in the IPv6 header of each such
autoconfiguration packet.
In some cases, a mobile node may already know a (constant) IPv6
address that has been assigned to it for its use only while
visiting a specific foreign link. For example, a mobile node may be
statically configured with an IPv6 address assigned by the system
administrator of some foreign link, for its use while visiting that
link. If so, rather than using address autoconfiguration to form a
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new care-of address using this subnet prefix, the mobile node MAY use
its own pre-assigned address as its care-of address on this link.
10.4.
10.5. Sending Binding Updates to the Home Agent
After deciding to change its primary care-of address as described
in Sections 10.2 10.3 and 10.3, 10.4, a mobile node MUST register this care-of
address with its home agent in order to make this its primary care-of
address. To do so, the mobile node sends a packet to its home agent
containing a Binding Update option, with the packet constructed as
follows:
- The Home Registration (H) bit MUST be set in the Binding Update.
- The Acknowledge (A) bit MUST be set in the Binding Update.
- The packet MUST contain a Home Address option, giving the mobile
node's home address for the binding.
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- The care-of address for the binding MUST be used as the Source
Address in the packet's IPv6 header, or the Care-of Address
Present (C) bit MUST be set in the Binding Update and the care-of
address for the binding MUST be specified in the Care-of Address
field in the Binding Update.
- The Prefix Length field SHOULD be set to the length of the mobile
node's subnet prefix in its home address, to request the mobile
node's home agent to serve as a home agent for all home addresses
for the mobile node based on all on-link subnet prefixes on the
home link. Otherwise, this field MUST be set to zero.
The Acknowledge (A) bit in the Binding Update requests the home
agent to return a Binding Acknowledgement in response to this
Binding Update. As described in Section 5.2, the mobile node SHOULD
retransmit this Binding Update to its home agent until it receives
a matching Binding Acknowledgement. Once reaching a retransmission
timeout period of MAX_BINDACK_TIMEOUT, the mobile node SHOULD
continue to periodically retransmit the Binding Update at this rate
until acknowledged (or until it begins attempting to register a
different primary care-of address).
The Prefix Length field in the Binding Update allows the mobile node
to request its home agent to serve all home addresses for the mobile
node, as indicated by the interface identifier in the mobile node's
home address (the remaining low-order bits after the indicated subnet
prefix), together with each on-link subnet prefix on the home link.
Until the lifetime of this registration expires, the home agent
considers itself the home agent for each such home address of the
mobile node. As the set of on-link subnet prefixes on the home link
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changes over time, the home agent changes the set of home addresses
for this mobile node for which it is serving as the home agent.
If the mobile node has additional home addresses using a different
interface identifier, then the mobile node SHOULD send an additional
packet containing a Binding Update to its home agent to register
the care-of address for each such other home address (or set of
home addresses sharing an interface identifier). These additional
Binding Updates MUST each be sent as a separate packet, since each
MUST contain an AH [8] or ESP [9] header to authenticate the Binding
Update as coming from the home address being bound.
10.6. Dynamic Home Agent Address Discovery
It is possible that when the mobile node needs to send such a Binding
Update to its home agent, that agent to register its new primary care-of address,
as described in Section 10.5, the mobile node does may not know the
address of any router on its home link that can serve as a home agent
for it. For example, some nodes on its home link may have been
reconfigured while the mobile node has been away from home, such that
the router that was operating as the mobile node's home agent has
been replaced by a different router serving this role.
In this case, the mobile node SHOULD use the dynamic home agent
address discovery procedure to find the address of a suitable home
agent on its home link. To do so, the mobile node sends the packet,
as described above, with the Destination Address in the packet's IPv6
header set to the Home-Agents anycast address for its home subnet
prefix. As described in Section 9.2, the home agent on its home link
that receives this Binding Update will reject the Update, returning
to the mobile node the home agent's own global unicast IP address
along with a list of the global unicast IP addresses of each other
home agent operating on the home link. The mobile node SHOULD then
retransmit its Binding Update to one of these homes agent using the
provided global unicast address; the mobile node MAY re-attempt
this home registration with each of these home agents in turn, by
sending each a Binding Update and waiting for the matching Binding
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Acknowledgement, until its registration is accepted by one of these
home agents.
If the mobile node has a current registration with some home agent
on its home link (the Lifetime for that registration has not yet
expired), then the mobile node MUST attempt any new registration
first with that home agent. If that registration attempt fails
(e.g., times out or is rejected), the mobile node SHOULD then
reattempt this registration with another home agent on its home link.
If the mobile node knows of no other suitable home agent, then it MAY
attempt the dynamic home agent address discovery procedure described
above.
10.5.
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10.7. Sending Binding Updates to Correspondent Nodes
A mobile node MAY send a Binding Update to any correspondent node at
any time to allow it to cache its current care-of address (subject to
the rate limiting defined in Section 10.8). 10.10). In any Binding Update
sent by a mobile node, the care-of address (either the Source Address
in the packet's IPv6 header or the Care-of Address field in the
Binding Update) MUST be set to one of the care-of addresses currently
in use by the mobile node or to the mobile node's home address.
If set to one of the mobile node's current care-of addresses (the
care-of address given MAY differ from the mobile node's primary
care-of address), the Binding Update requests the correspondent node
to create or update an entry for the mobile node in the correspondent
node's Binding Cache to record this care-of address for use in
sending future packets to the mobile node. In this case, the
Lifetime value sent in the Binding Update MUST be no greater than
the remaining lifetime of the mobile node's home registration of its
primary care-of address at its home agent.
If, instead, the care-of address is set to the mobile node's home
address, the Binding Update requests the correspondent node to delete
any existing Binding Cache entry that it has for the mobile node.
A mobile node MAY set the care-of address differently for sending
Binding Updates to different correspondent nodes.
When sending any Binding Update, the mobile node MUST record in its
Binding Update List the following fields from the Binding Update:
- The IP address of the node to which the Binding Update was sent.
- The home address for which the Binding Update was sent, sent.
- The remaining lifetime of the binding, initialized from the
Lifetime field sent in the Binding Update.
The mobile node MUST retain in its Binding Update List information
about all Binding Updates sent, for which the lifetime of the binding
has not yet expired. When However, when sending a Binding Update, if an
entry already exists in the mobile node's Binding Update List for
an earlier Binding Update sent to that same destination node, the
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existing Binding Update List entry is updated to reflect the new
Binding Update rather than creating a new Binding Update List entry.
In general, when a mobile node sends a Binding Update to its home
agent to register a new primary care-of address (as described in
Section 10.4), 10.5), the mobile node will also send a Binding Update to
each correspondent other node for which an entry exists in the mobile node's
Binding Update List. Thus, correspondent other relevant nodes are generally kept
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updated about the mobile node's binding and can send packets directly
to the mobile node using the mobile node's current care-of address.
The mobile node, however, need not send these Binding Updates
immediately after configuring a new care-of address. For example,
since the Binding Update is a destination option and can be included
in any packet sent by a mobile node, the mobile node MAY delay
sending a new Binding Update to any correspondent node for a
short period of time, in hopes that the needed Binding Update
can be included in some packet that the mobile node sends to that
correspondent node for some other reason (for example, as part of
some TCP connection in use). In this case, when sending a packet
to some correspondent node, the mobile node SHOULD check in its
Binding Update List to determine if a new Binding Update to this
correspondent node is needed, and SHOULD include the new Binding
Update in this packet as necessary.
In addition, when a mobile node receives a packet for which the
mobile node can deduce that the original sender of the packet has
no Binding Cache entry for the mobile node, or for which the mobile
node can deduce that the original sender of the packet has an
out-of-date care-of address for the mobile node in its Binding Cache,
the mobile node SHOULD return a Binding Update to the sender giving
its current care-of address. address (subject to the rate limiting defined
in Section 10.10). In particular, the mobile node SHOULD return a
Binding Update in response to receiving a packet that meets all of
the following tests:
- The packet was tunneled using IPv6 encapsulation.
- The Destination Address in the tunnel (outer) IPv6 header is
equal to any of the mobile node's care-of addresses.
- The Destination Address in the original (inner) IPv6 header
is equal to one of the mobile node's home address. If the original packet
contains a Routing header, the final Address indicated in the
Routing header should be used in addresses; or this comparison rather than the
Destination Address in is equal to one of the original IPv6 header. mobile node's previous
care-of addresses, if the mobile node has an entry in its Binding
Update List representing an unexpired Binding Update sent to
a previous default router for this previous care-of address
(Section 10.8).
- The Source Address in the tunnel (outer) IPv6 header differs from
the Source Address in the original (inner) IPv6 header.
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The destination address to which the Binding Update should be sent
in response to receiving a packet meeting all of the above tests above, is
the Source Address in the original (inner) IPv6 header of the packet.
The home address for which this Binding Update is sent should be the
Destination Address of the original (inner) packet.
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Binding Updates sent to correspondent nodes are not generally
required to be acknowledged. However, if the mobile node wants
to be sure that its new care-of address has been added to entered into a
correspondent node's Binding Cache, the mobile node MAY request an
acknowledgement by setting the Acknowledge (A) bit in the Binding
Update. In this case, however, the mobile node SHOULD NOT continue
to retransmit the Binding Update once the retransmission timeout
period has reached MAX_BINDACK_TIMEOUT.
A mobile node MAY choose to keep its location private from certain
correspondent nodes, and thus need not send new Binding Updates to
those correspondents. A mobile node MAY also send a Binding Update
to such a correspondent node to instruct it to delete any existing
binding for the mobile node from its Binding Cache, as described in
Section 5.1. No other IPv6 nodes are authorized to send Binding
Updates on behalf of a mobile node.
10.6.
10.8. Sending Binding Updates to the Previous Default Router
After switching to a new default router (and thus also changing its
primary care-of address), a mobile node MAY send a Binding Update to
its previous default router, giving its new care-of address. The
packet carrying the Binding Update MUST be addressed to the mobile
node's previous default router's global unicast address, learned
by the mobile node based on Prefix Information options received in
Router Advertisements from it in which the Router Address (R) bit is
set.
If the mobile node sends such a Binding Update, the home address
for the binding, specified in the Home Address option included in
the packet carrying this Binding Update, MUST be set the mobile
node's old primary care-of address (that it used while using this
default router), and the care-of address for the binding (either the
Source Address in the packet's IPv6 header or the Care-of Address
field in the Binding Update) MUST be set to the mobile node's new
primary care-of address. In addition, the Home Registration (H)
bit MUST also be set in this Binding Update, to request the mobile
node's previous default router to temporarily act as a home agent
for the mobile node's old primary care-of address. The previous
default router mobile node's old primary care-of address. The previous
default router will thus tunnel packets for the mobile node to its
new care-of address. All of the procedures defined for home agent
operation must be followed by this previous default router for this
registration. Note that the previous router does not necessarily
know the mobile node's (permanent) home address as part of this
registration.
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10.9. Retransmitting Binding Updates
If, after sending a Binding Update in which the Acknowledge (A) bit
is set, a mobile node fails to receive a Binding Acknowledgement
within INITIAL_BINDACK_TIMEOUT seconds, the mobile node SHOULD
retransmit the Binding Update until a Binding Acknowledgement
is received. Such a retransmitted Binding Update MUST use the
same Sequence Number value as the original transmission. The
retransmissions by the mobile node MUST use an exponential
back-off process, in which the timeout period is doubled
upon each retransmission until either the node receives a
Binding Acknowledgement or the timeout period reaches the value
MAX_BINDACK_TIMEOUT.
10.10. Rate Limiting for Sending Binding Updates
A mobile node MUST NOT send Binding Updates more often than once per
MAX_UPDATE_RATE seconds to any node. After sending MAX_FAST_UPDATES
consecutive Binding Updates to a particular node with the same
care-of address, the mobile node SHOULD reduce its rate of sending
Binding Updates to that node, to the rate of SLOW_UPDATE_RATE per
second. The mobile node MAY continue to send Binding Updates at this
slower rate indefinitely, in hopes that the node will thus tunnel eventually
be able to process a Binding Update and begin to route its packets for
directly to the mobile node to at its new care-of address. All of the procedures defined for home agent
operation must be followed by this previous default router for this
registration. Note that the previous router does not necessarily
know the mobile node's (permanent) home address as part of this
registration.
10.7. Retransmitting
10.11. Receiving Binding Updates
If, after sending Acknowledgements
Upon receiving a packet carrying a Binding Update Acknowledgement, a mobile
node MUST validate the packet according to the following tests:
- The packet contains a valid AH [8] or ESP [9] header providing
sender authentication, data integrity protection, and replay
protection.
- The Option Length field in which the Acknowledge (A) bit option is set, a greater than or equal to
11 octets.
- The Sequence Number field matches the Sequence Number sent by the
mobile node fails to receive a this destination address in an outstanding Binding
Update.
Any Binding Acknowledgement not satisfying all of these tests MUST be
silently ignored, although the remainder of the packet (i.e., other
options, extension headers, or payload) SHOULD be processed normally
according to any procedure defined for that part of the packet.
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within INITIAL_BINDACK_TIMEOUT seconds,
When a mobile node receives a packet carrying a valid Binding
Acknowledgement, the mobile node MUST examine the Status field as
follows:
- If the Status field indicates that the Binding Update was
accepted (the Status field is less than 128), then the mobile
node SHOULD
retransmit MUST update the corresponding entry in its Binding Update until a Binding Acknowledgement
is received. Such a retransmitted
List to indicate that the Binding Update MUST use he
same Sequence Number value as the original transmission. has been acknowledged.
The
retransmissions by the mobile node MUST use an exponential
back-off process, in which the timeout period is doubled
upon each retransmission until either then stop retransmitting the node receives a Binding Acknowledgement or Update.
- If the timeout period reaches Status field indicates that the value
MAX_BINDACK_TIMEOUT.
10.8. Rate Limiting for Sending Binding Updates
A Update was
rejected (the Status field is greater than or equal to 128), then
the mobile node MUST NOT send delete the corresponding Binding Updates more often than once per
MAX_UPDATE_RATE seconds to any node. After sending MAX_FAST_UPDATES
consecutive Update List
entry (and MUST also stop retransmitting the Binding Updates Update).
Optionally, the mobile node MAY then take steps to correct the
cause of the error and retransmit the Binding Update (with a particular node with new
Sequence Number value), subject to the same
care-of address, rate limiting restriction
specified in Section 10.10. In particular, if the Status field
is equal to 135 (dynamic home agent address discovery response),
then the mobile node SHOULD reduce MAY reattempt its rate home registration with
the home agent address given in the Source Address field of sending the
packet carrying the Binding Updates to that node, Acknowledgement or with any of the
home agent IP addresses listed in the Home Agents List field in
the Binding Acknowledgement. If any of these addresses is not a
global unicast address or does not have a subnet prefix equal to
the rate of SLOW_UPDATE_RATE per
second. The mobile node MAY continue to send Binding Updates at the
slower rate indefinitely, in hopes node's own subnet prefix, then that the node will eventually particular address
MUST be able to process a Binding Update ignored and begin to route its packets
directly to the mobile node at MUST NOT reattempt its new care-of address.
10.9. home
registration with that home agent.
10.12. Receiving ICMP Error Messages
The Option Type value for a Binding Update option specifies that
any Requests
When a mobile node receiving this option that does not recognize the Option
Type receives a packet containing a Binding Request,
it SHOULD return an ICMP Parameter Problem, Code 2, message to the sender of the a packet containing the Binding Update option. If
a node sending a Binding Update receives such an ICMP error message
in response, it should record Update.
The Lifetime field in its this Binding Update List that future
Binding Updates should not SHOULD be sent to this destination.
Likewise, although ALL IPv6 nodes (whether host or router, whether
mobile or stationary) MUST implement the ability set to receive packets
containing a Home Address option, all Option Type values in IPv6
include a specification of the behavior that a node receiving new
lifetime, extending any current lifetime remaining from a
packet containing previous
Binding Update sent to this option performs if it does not implement
receipt of that type of option. For the Home Address option, the
Option Type value specifies that any node receiving (as indicated in any existing
Binding Update List entry for this option that
does not recognize the Option Type SHOULD return an ICMP Parameter
Problem, Code 2, message to node), except that this lifetime
MUST NOT exceed the sender of remaining lifetime for the packet containing mobile node's primary
care-of address registration at its home agent. When sending this
Binding Update, the
Home Address option. If a mobile node receives such an ICMP error
message from some node indicating that it does not recognize MUST update its Binding Update List
in the same way as for any other Binding Update sent by the mobile node's Home Address option,
node.
Note, however, that the mobile node SHOULD log MAY choose to keep its current
binding private from the
error and then discard sender of the ICMP message; Binding Request. In this error message indicates
that
case, the mobile node instead SHOULD returns a Binding Update to the
sender, in which the original packet was addressed (the node
returning Lifetime field is set to zero and the ICMP error message) does not correctly implement this
required part of care-of
address is set to the IPv6 protocol. mobile node's home address.
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10.10.
10.13. Receiving Binding Acknowledgements
Upon receiving a packet carrying ICMP Error Messages
The Option Type value for a Binding Acknowledgement, a mobile Update option specifies that
any node MUST validate receiving this option that does not recognize the packet according Option
Type SHOULD return an ICMP Parameter Problem, Code 2, message to
the following tests:
- The packet contains either an AH [7] or ESP [8] header providing sender authentication, data integrity protection, and replay
protection.
- The Option Length field in the option is greater than or equal to
11 octets.
- The Sequence Number field matches of the Sequence Number sent by packet containing the
mobile Binding Update option. If
a node to this destination address in sending a Binding Update receives such an outstanding ICMP error message
in response, it should record in its Binding
Update.
Any Update List that future
Binding Acknowledgement Updates should not satisfying all of these tests MUST be
silently ignored, sent to this destination.
Likewise, although the remainder of the packet (i.e., other
options, extension headers, ALL IPv6 nodes (whether host or payload) SHOULD be processed normally
according router, whether
mobile or stationary) MUST implement the ability to any procedure defined for that part correctly process
received packets containing a Home Address option, all Option Type
values in IPv6 include a specification of the packet.
When behavior that a mobile node receives
receiving a packet carrying a valid Binding
Acknowledgement, the mobile node MUST examine the Status field as
follows:
- If the Status field indicates containing this option performs if it does not
implement receipt of that type of option. For the Binding Update was
accepted (the Status field is less than 128), then Home Address
option, the mobile Option Type value specifies that any node MUST update receiving
this option that does not recognize the corresponding entry in its Binding Update
List Option Type SHOULD return
an ICMP Parameter Problem, Code 2, message to indicate that the Binding Update has been acknowledged.
The mobile node MUST thus stop retransmitting sender of the Binding Update.
- If
packet containing the Status field indicates Home Address option. If a mobile node receives
such an ICMP error message from some node indicating that it does
not recognize the Binding Update was
rejected (the Status field is greater than or equal to 128), then mobile node's Home Address option, the mobile
node MUST delete SHOULD log the corresponding Binding Update List
entry (and MUST also stop retransmitting error and then discard the Binding Update).
Optionally, ICMP message; this
error message indicates that the mobile node MAY then take steps to correct which the
cause of original packet
was addressed (the node returning the ICMP error and retransmit the Binding Update (with a new
Sequence Number value), subject to message) does not
correctly implement this required part of the rate limiting restriction
specified in IPv6 protocol.
10.14. Receiving Tunneled Router Advertisements
Section 10.8. In particular, if 9.7 describes the Status field
is equal to 135 (dynamic operation of a home agent address discovery response),
then the to support
renumbering a mobile node MAY reattempt its node's home registration with any
of subnet while the mobile node is
away from home. The home agent IP addresses listed in tunnels certain Router Advertisement
messages to the Other Home Agents
field mobile node while away from home, giving "important"
Prefix Information options that describe changes in the Binding Acknowledgement or with prefixes in
use on the mobile node's home agent
address given in link.
When a mobile node receives a tunneled Router Advertisement, it MUST
validate it according to the following tests:
- The Source Address field of the IP packet carrying the Binding Acknowledgement. If any of these addresses Router
Advertisement is not
unicast a address or does not have a subnet prefix equal to the
mobile node's own subnet prefix, then that particular same as the home agent address
MUST be ignored and to which the
mobile node MUST NOT reattempt last sent an accepted "home registration" Binding
Update to register its home
registration with that home agent. primary care-of address.
- The packet contains either an AH [8] or ESP [9] header providing
sender authentication, data integrity protection, and replay
protection.
- The packet contains a Binding Request destination option.
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10.11. Receiving Binding Requests
When
Any received tunneled Router Advertisement not meeting all of these
tests MUST be silently discarded.
If a received tunneled Router Advertisement is not discarded
according to the tests listed above, the mobile node receives a packet containing a Binding Request, MUST process the
Router Advertisement as if it SHOULD return were connected to the sender a packet containing a Binding Update.
The Lifetime field its home link [13].
Such processing MAY result in this Binding Update SHOULD be set to the mobile node configuring a new
lifetime, extending any current lifetime remaining from a previous
Binding Update sent home
address, although due to this node (as indicated in any existing
Binding Update List entry for this node). When sending this Binding
Update, separation between preferred lifetime and
valid lifetime, such changes should not affect most communication by
the mobile node MUST update its Binding Update List node, in the same way as for any other Binding Update sent by the mobile node.
Note, however, nodes that the mobile node MAY choose to keep its current
binding private from the sender of the Binding Request. are at home.
In addition, in processing the packet containing this
case, Router
Advertisement, the mobile node instead SHOULD returns return to the home agent a
Binding Update in response to the
sender, Binding Request carried in which the Lifetime field is set
packet. The correct formation of this Binding Update by the mobile
node and processing of it by the home agent will be viewed by the
home agent as an acknowledgement of this Router Advertisement,
confirming to zero.
10.12. it that this Router Advertisement was received by the
mobile node.
10.15. Using Multiple Care-of Addresses
As described in Section 10.3, 10.4, a mobile node MAY use more than one
care-of address at a time. Particularly in the case of many wireless
networks, a mobile node effectively might be reachable through
multiple links at the same time (e.g., with overlapping wireless
cells), on which different on-link subnet prefixes may exist. A
mobile node SHOULD select a primary care-of address from among those
care-of addresses it has formed using any of these subnet prefixes,
based on the movement detection mechanism in use, as described in
Section 10.2. 10.3. When the mobile node selects a new primary care-of
address, it MUST register it with its home agent through by sending it a
Binding Update with the Home Registration (H) and Acknowledge (A)
bits set, as described in Section 10.4. 10.5.
To assist with smooth handoffs, a mobile node SHOULD retain
its previous primary care-of address as a (non-primary) care-of
address, and SHOULD still accept packets at this address, even after
registering its new primary care-of address with its home agent.
This is reasonable, since the mobile node could only receive packets
at its previous primary care-of address if it were indeed still
connected to that link. If the previous primary care-of address was
allocated using stateful address autoconfiguration [2], the mobile
node may not wish to release the address immediately upon switching
to a new primary care-of address.
10.13.
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10.16. Routing Multicast Packets
A mobile node that is connected to its home link functions in the
same way as any other (stationary) node. Thus, when it is at home,
a mobile node functions identically to other multicast senders and
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receivers. This section therefore describes the behavior of a mobile
node that is not on its home link.
In order to receive packets sent to some multicast group, a mobile
node must join that multicast group. One method by which a mobile
node MAY join the group is via a (local) multicast router on the
foreign link being visited. The mobile node SHOULD use its care-of
address sharing a subnet prefix with the multicast router, as
the source IPv6 address of its multicast group membership control
messages.
Alternatively, a mobile node MAY join multicast groups via a
bi-directional tunnel to its home agent. The mobile node tunnels the
appropriate its
multicast group membership control packets to its home agent, and the
home agent forwards multicast packets down the tunnel to the mobile
node.
A mobile node that wishes to send packets to a multicast group
also has two options: (1) send directly on the foreign link being
visited; or (2) send via a tunnel to its home agent. Because
multicast routing in general depends upon the Source Address used in
the IPv6 header of the multicast packet, a mobile node that tunnels a
multicast packet to its home agent MUST use its home address as the
IPv6 Source Address of the inner multicast packet.
10.14.
10.17. Returning Home
A mobile node detects that it has returned to its home link through
the movement detection algorithm in use (Section 10.2), 10.3), when the
mobile node detects that its home subnet prefix is again on-link.
The mobile node SHOULD then send a Binding Update to its home agent,
to instruct its home agent to no longer intercept or tunnel packets
for it. In this Binding Update, the mobile node MUST set the care-of
address for the binding (the Source Address field in the packet's
IPv6 header) to the mobile node's own home address. As with other
Binding Updates sent to register with its home agent, the mobile
node MUST set the Acknowledge (A) and Home Registration (H) bits,
and SHOULD retransmit the Binding Update until a matching Binding
Acknowledgement is received.
In addition, the mobile node MUST multicast onto the home link
(to the all-nodes multicast address) a Neighbor Advertisement
message [11], [13], to advertise the mobile node's own link-layer address
for its own home address. The Target Address in this Neighbor
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Advertisement message MUST be set to the mobile node's home address,
and the Advertisement MUST include a Target Link-layer Address option
specifying the mobile node's link-layer address. The mobile node
MUST multicast such a Neighbor Advertisement message for each of its
home addresses, as defined by the current on-link prefixes, including
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its link-local address and site-local address. The Solicited
Flag (S) in these Advertisements MUST NOT be set, since they were
not solicited by any Neighbor Solicitation message. The Override
Flag (O) in these Advertisements MUST be set, indicating that the
Advertisements SHOULD override any existing Neighbor Cache entries at
any node receiving them.
Since multicasts on the local link (such as Ethernet) are typically
not guaranteed to be reliable, the mobile node MAY retransmit these
Neighbor Advertisement messages up to MAX_ADVERT_REXMIT times to
increase their reliability. It is still possible that some nodes on
the home link will not receive any of these Neighbor Advertisements,
but these nodes will eventually be able to recover through use of
Neighbor Unreachability Detection [11]. [13].
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11. Constants
INITIAL_BINDACK_TIMEOUT 1 second
MAX_BINDACK_TIMEOUT 256 seconds
MAX_UPDATE_RATE once per second
SLOW_UPDATE_RATE once per 10 seconds
MAX_FAST_UPDATES 5 transmissions
MAX_ADVERT_REXMIT 3 transmissions
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12. IANA Considerations
This document defines four new types of IPv6 destination options,
each of which must be assigned an Option Type value:
- The Binding Update option, described in Section 5.1
- The Binding Acknowledgement option, described in Section 5.2
- The binding Request option, described in Section 5.3
- The Home Address option, described in Section 5.4
In addition, this document defines a two new Neighbor Discovery [11]
option, [13]
options, which must be assigned an Option Type value values within the option
numbering space for Neighbor Discovery messages:
- The Advertisement Interval option, described in Section 6.2. 6.3.
- The Home Agent Information option, described in Section 6.4.
Finally, this document defines a new type of anycast address, which
must be assigned a reserved interface identifier value for use with any subnet prefix to
define this anycast address on each subnet:
- The Home-Agents anycast address, used in the dynamic home agent
address discovery procedure described in Sections 9.2 and 10.4. 10.6.
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13. Security Considerations
13.1. Binding Updates, Acknowledgements, and Requests
The Binding Update option described in this document will result
in packets addressed to a mobile node being delivered instead to
its care-of address. This ability to change the routing of these
packets could be a significant vulnerability if any packet containing
a Binding Update option was not authenticated. Such use of "remote
redirection", for instance as performed by the Binding Update option,
is widely understood to be a security problem in the current Internet
if not authenticated [1].
The Binding Acknowledgement option also requires authentication,
since, for example, an attacker could otherwise trick a mobile node
into believing a different outcome from a registration attempt with
its home agent.
No authentication is required for the Binding Request option, since
the use of this option does not modify or create any state in either
the sender or the receiver. The Binding Request option does open
some issues with binding privacy, but those issues can be dealt with
either through existing IPsec encryption mechanisms or through use of
firewalls.
The existing IPsec replay protection mechanisms allow a "replay
protection window" to support receiving packets out of order.
Although appropriate for many forms of communication, Binding Updates
MUST be applied only in the order sent. The Binding Update option
thus includes a Sequence Number field to provide this necessary
sequencing. The use of this Sequence Number together with IPsec
replay protection is similar in many ways, for example, to the the
sequence number in TCP. IPsec provides strong replay protection but
no ordering, and the sequence number provides ordering but need not
worry about replay protection such as through the sequence number
wrapping around.
13.2. Home Address Options Option
No special authentication of the Home Address option is required,
except that if the IPv6 header of a packet is covered by
authentication, then that authentication MUST also cover the Home
Address option; this coverage is achieved automatically by the
definition of the Option Type code for the Home Address option
(Section 5.4), since it indicates that the option is included in the
authentication computation. Thus, even when authentication is used
in the IPv6 header, the security of the Source Address field in the
IPv6 header is not compromised by the presence of a Home Address
option. Without authentication of the packet, then any field in the
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IPv6 header, including the Source Address field, and any other parts
of the packet, including the Home Address option, can be forged or
modified in transit. In this case, the contents of the Home Address
option is no more suspect than any other part of the packet.
The use of the Home Address option allows packets sent by a
mobile node to pass normally through routers implementing ingress
filtering [6]. Since the care-of address used in the Source Address
field of the packet's IPv6 header is topologically correct for the
sending location of the mobile node, ingress filtering can trace the
location of the mobile node in the same way as can be done with any
sender when ingress filtering is in use.
However, if a node receiving a packet that includes a Home Address
option implements the processing of this option by physically
copying the Home Address field from the option into the IPv6 header,
replacing the Source Address field there, then the ability to
trace the true location of the sender is removed once this step
in the processing is performed. This diminishing of the power of
ingress filtering only occurs once the packet has been received at
its ultimate destination, and does not affect the capability of
ingress filtering while the packet is in transit. Furthermore, this
diminishing can be entirely eliminated by appropriate implementation
techniques in the receiving node. For example, the original contents
of the Source Address field (the sending care-of address) could be
saved elsewhere in memory with the packet, until all processing of
the packet is completed.
13.3. General Mobile Computing Issues
The mobile computing environment is potentially very different from
the ordinary computing environment. In many cases, mobile computers
will be connected to the network via wireless links. Such links
are particularly vulnerable to passive eavesdropping, active replay
attacks, and other active attacks. Furthermore, mobile computers
are more susceptible to loss or theft than stationary computers.
Any secrets such as authentication or encryption keys stored on the
mobile computer are thus subject to compromise in ways generally not
common in the non-mobile environment.
Users who have sensitive data that they do not wish others to have
access to should use additional mechanisms (such as encryption) to
provide privacy protection, but such mechanisms are beyond the scope
of this document. Users concerned about traffic analysis should
consider appropriate use of link encryption. If stronger location
privacy is desired, the mobile node can create a tunnel to its home
agent. Then, packets destined for correspondent nodes will appear
to emanate from the home subnet, and it may be more difficult to
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pinpoint the location of the mobile node. Such mechanisms are all
beyond the scope of this document.
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Changes from Previous Draft
This appendix briefly lists some of the major changes in this
draft relative to the previous version of this same draft,
draft-ietf-mobileip-ipv6-04.txt:
- Replaced the ID Length field in the Binding Update with the
Prefix Length field.
- Added a definition of "interface identifier" in Section 3.1.
- Added a description of dynamic home agent address discovery to
the basic operation overview in Section 4.1.
- Added a description of the new Home Agents List conceptual data
structure in Section 4.3. This list is used in the dynamic home
agent address discovery mechanism.
- Added some of the Other Home Agents field major changes in this
draft relative to the Binding Acknowledgement
option format, and modified the description previous version of this same draft,
draft-ietf-mobileip-ipv6-05.txt:
- Clarified that the setting
for the Option Length field Advertisement Interval option in the Binding Acknowledgement to
accommodate the Other Home Agents field. This field is used Section 6.3
MAY be included in
the dynamic Router Advertisements by any router, not just
by home agent address discovery mechanism. agents.
- Added Modified Section 9.1, describing the processing performed by 6.5 to document a
home agent required change to maintain its Home Agents List when the home agent
receives a valid Router Advertisement message
MaxRtrAdvInterval limit, in which the Home
Agent (H) bit is set.
- Revised addition to the description of dynamic home agent address discovery
in Section 9.2 change to include use of the new Home Agents List
MinRtrAdvInterval limit, and
the return of the IP addresses from this list in the Other Home
Agents field of the Binding Acknowledgement clarified that rejects the
anycast Binding Update. these new limits MAY
be used by any router, not just by home agents.
- Revised Added Section 10.10 6.6 to include document new limits on sending Router
Solicitations by a description of the Other Home
Agents field in mobile node while away from home. These
changes are related to the received Binding Acknowledgement. MAX_RTR_SOLICITATIONS and
RTR_SOLICITATION_INTERVAL Neighbor Discovery constants.
- Added Section 6, listing modifications 6.2 documenting a modification to IPv6 Neighbor
Discovery: The the format of
a Prefix Information option for use in Router Advertisement message is changed
messages. This modification allows a router to
include the Home Agent (H) bit, easily and
efficiently advertise its own global unicast address.
- Defined a new Advertisement Interval
option is defined Home Agent Information Option for Router Advertisement messages,
Advertisements (Section 6.4). This option allows those routers
functioning as a home agent to optionally specify a preference
(relative to other home agents on this link) and the
value of MinRtrAdvInterval a lifetime for
this advertisement for providing home agent service. Use of this
option by home agents is allowed to be less
than the generic limit for routers of 3 seconds [11]. optional.
- Added a description in the IANA Considerations in Section 12, of
the need to assign an Option Type value for the new Advertisement
Interval option that can appear on Router Advertisement messages.
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- Changed 10.2, defining the rule in Section 9.3 dealing with forwarding
site-local-addressed packets general procedures to be used
by a mobile node in receiving packets while the mobile
nodes is away from home. Such In
particular, for packets now MUST NOT be tunneled
to the mobile node, unless the mobile node's registered primary
care-of address is within the same site as the mobile node's home
address.
- Added received with a description in Section 10.9 Routing header, this
section defines an exception for any use of what a mobile node should
do if it receives an ICMP Parameter Problem error message in Routing header
automatically derived by "reversing" the received Routing header,
for any response to packets sent by upper-layer protocols.
- Changed the Home Address option in some packet that it
sent. Although ALL IPv6 nodes MUST implement receipt treatment of packets
containing addressed to a Home Address option, mobile node's
site-local address while the encoding mobile node is away from home. The
current consensus of an Option Type
value in IPv6 always specifies some behavior for the case in
which the receiver does not recognize that type of option.
- In Section 10.2, changed SHOULD to MAY in specifying Mobile IP Working Group is that upon
lower-layer indication of link-layer mobility, such
packets SHOULD be tunneled to the mobile node
MAY send Router Solicitation messages by default, but
this behavior MUST be configurable to determine if new routers disable it; currently,
the exact definition and semantics of a "site" and a site-local
address are present on its new link.
- Also undefined in Section 10.2, added IPv6, and this default behavior might
change at some point in the future.
- Added a description definition of how the value
specified in the Advertisement Interval option in received
Router Advertisements MAY be used treatment of multicast packets
addressed to a multicast group to which a mobile node is
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subscribed, for which the multicast scope is link-local,
site-local, organization-local, etc. As with packets sent to a
mobile node's movement
detection algorithm.
- Moved the section on routing link-local and site-local addresses, link-local
multicast packets MUST NOT be tunneled to and from a the mobile host while away from home, node, and
multicast packets addressed to now be Section 10.13, a subsection of multicast address with scope
larger than link-local but smaller than global (e.g., site-local
and organization-local) SHOULD be tunneled to the description of mobile node operation
(Section 10), rather than being a separate section on its own.
This better integrates by
default, but this operation into the document. behavior MUST be configurable to disable it.
- Corrected the specification of the length of the Binding Update
option. The correct length is 24, not 16, if Added Section 7.2, detailing Mobile IP requirements on all IPv6
routers. They SHOULD be able to send an Advertisement Interval
option in their Router Advertisements, and SHOULD be able to
support sending unsolicited multicast Router Advertisements at
the Care-of Address
Present (C) bit is set. faster rate described in Section 6.5.
- Corrected Added Section 10.14 describing the specification mobile node side of
renumbering the length of home network, matching the Binding
Acknowledgement option. The correct length is 11, not 12 (plus
16 times home agent processing
described in Section 9.7.
- Simplified the number sequence of addresses listed tests in Section 9.4 performed by a
home agent being requested to no longer serve as the Other Home Agents
field sending
mobile node's home agent.
- Clarified in the Acknowledgement). Section 10.5 that if a mobile node has multiple home
addresses using different interface identifiers, then it SHOULD
send a separate Binding Update to its home agent for each.
- Other minor clarifications and correction Finally filled in Section 2, giving a comparison of typographical errors
throughout. Mobile IPv6
with Mobile IP for IPv4.
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Acknowledgements
We would like to thank the members of the Mobile IP and IPng Working
Groups for their comments and suggestions on this work. We would
particularly like to thank Josh Broch, Thomas Narten, Erik Nordmark,
and Jim Solomon for their detailed reviews of earlier versions of
this draft. Their suggestions have helped to improve both the design
and presentation of the protocol.
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References
[1] S. M. Bellovin. Security problems in the TCP/IP protocol suite.
ACM Computer Communications Review, 19(2), March 1989.
[2] Jim Bound and Charles Perkins. Dynamic Host Configuration
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draft-ietf-dhc-dhcpv6-10.txt, May 1997. Work in progress.
[3] Scott Bradner. Key words for use in RFCs to indicate
requirement levels. RFC 2119, March 1997.
[4] Alex Conta and Stephen Deering. Generic packet
tunneling in IPv6 specification. Internet-Draft,
draft-ietf-ipngwg-ipv6-tunnel-07.txt, December 1996.
Work in progress.
[5] Stephen E. Deering and Robert M. Hinden. Internet
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progress.
[6] Paul Ferguson and Daniel Senie. Network ingress filtering:
Defeating denial of service attacks which employ IP source
address spoofing. RFC 2267, January 1998.
[7] Robert M. Hinden and Stephen E. Deering. IP Version 6
addressing architecture. Internet-Draft,
draft-ietf-ipngwg-addr-arch-v2-06.txt, January 1998. Work in
progress.
[8] Stephen Kent and Randall Atkinson. IP Authentication header.
Internet-Draft, draft-ietf-ipsec-auth-header-02.txt, October
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[8]
[9] Stephen Kent and Randall Atkinson. IP Encapsulating Security
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October 1997. Work in progress.
[9]
[10] Stephen Kent and Randall Atkinson. Security architecture for
the Internet Protocol. Internet-Draft,
draft-ietf-ipsec-arch-sec-02.txt, November 1997. Work in
progress.
[11] P. Mockapetris. Domain Names---concepts Names -- concepts and facilities.
RFC 1034, November 1987.
[10]
[12] P. Mockapetris. Domain Names---implementation Names -- implementation and
specification. RFC 1035, November 1987.
[11]
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[13] Thomas Narten, Erik Nordmark, and William Allen Simpson.
Neighbor Discovery for IP version 6 (IPv6). Internet-Draft,
draft-ietf-ipngwg-discovery-v2-00.txt, July 1997. Work in
progress.
[12]
[14] Charles Perkins. IP encapsulation within IP. RFC 2003, October
1996.
[13]
[15] Charles Perkins, editor. IP mobility support. RFC 2002,
October 1996.
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[14]
[16] Charles Perkins. Minimal encapsulation within IP. RFC 2004,
October 1996.
[15]
[17] Charles Perkins and David B. Johnson. Route optimization in
Mobile IP. Internet-Draft, draft-ietf-mobileip-optim-07.txt,
November 1997. Work in progress.
[18] David C. Plummer. An Ethernet address resolution protocol:
Or converting network protocol addresses to 48.bit Ethernet
addresses for transmission on Ethernet hardware. RFC 826,
November 1982.
[19] J. B. Postel. User Datagram Protocol. RFC 768, August 1980.
[16]
[20] J. B. Postel, editor. Transmission Control Protocol. RFC 793,
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[17]
[21] Joyce K. Reynolds and Jon Postel. Assigned numbers. RFC 1700,
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[18]
[22] Susan Thomson and Thomas Narten. IPv6 stateless address
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Chair's Address
The Working Group can be contacted via its current chairs:
Jim Solomon
Motorola, Inc.
1301 E. Algonquin Rd.
Schaumburg, IL 60196
RedBack Networks
1389 Moffett Park Drive
Sunnyvale, CA 94089-1134
USA
Phone: +1 847 576-2753 408 548-3583
Fax: +1 408 548-3599
E-mail: solomon@comm.mot.com solomon@rback.com
Erik Nordmark
Sun Microsystems, Inc.
2550 Garcia Avenue
Mt. View, CA 94041
USA
Phone: +1 415 786-5166
Fax: +1 415 786-5896
E-mail: nordmark@sun.com
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Authors' Addresses
Questions about this document can also be directed to the authors:
David B. Johnson
Carnegie Mellon University
Computer Science Department
5000 Forbes Avenue
Pittsburgh, PA 15213-3891
USA
Phone: +1 412 268-7399
Fax: +1 412 268-5576
E-mail: dbj@cs.cmu.edu
Charles Perkins
Sun Microsystems, Inc.
Technology Development Group
Mail Stop MPK15-214
Room 2682
901 San Antonio Road
Palo Alto, CA 94303
USA
Phone: +1 415 786-6464
Fax: +1 415 786-6445
E-mail: cperkins@eng.sun.com
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----