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Mobile IP Working Group David B. Johnson
INTERNET-DRAFT Carnegie Mellon University
Charles Perkins
IBM Corporation
13 June
26 November 1996
Mobility Support in IPv6
<draft-ietf-mobileip-ipv6-01.txt>
<draft-ietf-mobileip-ipv6-02.txt>
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 packets destined for the mobile
node directly to it at this care-of address.
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
working documents as Internet-Drafts.
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
material or to cite them other than as "work in progress."
To learn the current status of any Internet-Draft, please check
the "1id-abstracts.txt" listing contained in the Internet-Drafts
Shadow Directories on ftp.is.co.za (Africa), nic.nordu.net (Europe),
munnari.oz.au (Pacific Rim), ds.internic.net (US East Coast), or
ftp.isi.edu (US West Coast).
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Contents
Abstract i
Status of This Memo i
1. Introduction 1
1.1. Design Requirements
2. Terminology 2
2.1. General Terms . . . . . . . . . . . . . . . . . . . 2
1.2. Goals . . . 2
2.2. Mobile IPv6 Terms . . . . . . . . . . . . . . . . . . . . 3
2.3. Specification Language . . . 2
1.3. Assumptions . . . . . . . . . . . . . . 4
3. Overview of Mobile IPv6 Operation 6
4. New IPv6 Destination Options 11
4.1. Binding Update Option . . . . . . . . . 2
1.4. Applicability . . . . . . . . . 11
4.2. Binding Acknowledgement Option . . . . . . . . . . . . . 2
1.5. Terminology 14
4.3. Binding Request Option . . . . . . . . . . . . . . . . . 17
5. Requirements for IPv6 Nodes 18
6. Correspondent Node Operation 20
6.1. Receiving Binding Updates . . . . . . 3
1.6. Specification Language . . . . . . . . . . 20
6.2. Requests to Cache a Binding . . . . . . . 5
2. Overview of Mobile IPv6 Operation 7
3. Message and Option Formats 9
3.1. Binding Update Option . . . . . . . . 21
6.3. Requests to Delete a Binding . . . . . . . . . . 9
3.2. ICMP Binding Acknowledgement Message . . . . 21
6.4. Sending Binding Acknowledgements . . . . . . 13
4. Requirements for IPv6 Nodes 15
5. Binding Cache Management 17
5.1. Receiving Binding Updates . . . . . . 21
6.5. Cache Replacement Policy . . . . . . . . . . 17
5.2. Requests to Cache a Binding . . . . . . 22
6.6. Receiving ICMP Error Messages . . . . . . . . . 17
5.3. Requests to Delete a Binding . . . . . 23
6.7. Sending Packets to a Mobile Node . . . . . . . . . 18
5.4. Sending Binding Acknowledgements . . . 24
7. Home Agent Operation 26
7.1. Primary Care-of Address Registration . . . . . . . . . 18
5.5. Cache Replacement Policy . 26
7.2. Primary Care-of Address De-registration . . . . . . . . . 28
7.3. Tunneling Intercepted Packets to a Mobile Node . . . . . 28
7.4. Renumbering the Home Subnet . 19
5.6. Receiving ICMP Error Messages . . . . . . . . . . . . . . 19
6. 29
8. Mobile Node Considerations 21
6.1. Operation 31
8.1. Movement Detection . . . . . . . . . . . . . . . . . . . 21
6.2. 31
8.2. Forming New Care-of Addresses . . . . . . . . . . . . . . 23
6.3. 33
8.3. Sending Binding Updates to the Home Agent . . . . . . . . 24
6.4. 34
8.4. Sending Binding Updates to Correspondent Nodes . . . . . 25
6.5. 35
8.5. Sending Binding Updates to the Previous Default Router . 25
6.6. 37
8.6. Retransmitting Binding Updates . . . . . . . . . . . . . 37
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8.7. Rate Limiting for Sending Binding Updates . . . . . . . . 26
6.7. 38
8.8. Receiving Binding Acknowledgements . . . . . . . . . . . 26
6.8. 38
8.9. Using Multiple Care-of Addresses . . . . . . . . . . . . 27
6.9. 39
8.10. Returning Home . . . . . . . . . . . . . . . . . . . . . 28
7. Home Agent Considerations 29
7.1. Home Agent Care-of Address Registration . . . . . . . . . 29
7.2. Home Agent Care-of Address De-registration . . . . . . . 31
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7.3. Delivering 39
9. Routing Multicast Packets to a Mobile Node . . . 41
10. Constants 42
11. Security Considerations 43
Acknowledgements 44
A. Open Issues 45
A.1. Session Keys with Local Routers . . . . . . . . 32
7.4. Renumbering the Home Network . . . . . 45
A.2. Source Address Filtering by Firewalls . . . . . . . . . 32
8. Correspondent Node Considerations 34
8.1. Delivering Packets to a Mobile Node . 45
A.3. Dynamic Home Agent Address Discovery . . . . . . . . . . 34
9. Authentication and 46
A.4. Replay Protection 36
10. Routing Multicast Packets 37
11. Constants 38
Acknowledgements 38
References 39
A. Open Issues 40
A.1. Session Keys with Local Routers . . . . . . . . . . . . . 40
A.2. Source Address Filtering by Firewalls for Binding Updates . . . . . . . . . . 40 46
References 47
Chair's Address 42 49
Authors' Addresses 42 50
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1. Introduction
This document specifies the operation of mobile computers using
Internet Protocol Version 6 (IPv6) [6]. Mobile [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 IPv6 subnet, since routing is based on the network prefix in a
packet's destination IP address. In order continue communication
in spite of its movement, a mobile node could change its IP address
each time it moves to a new IPv6 subnet, 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, protocol operation defined here, known as Mobile IPv6, allows transparent routing of IPv6
packets to a
mobile nodes using node to move from one IPv6 subnet to another without changing
the mobile node's IP address. A mobile node is always addressable
by its "home address", the IP address assigned to the mobile node
within its home IPv6 address, subnet. Packets may be routed to it using this
address regardless of the mobile node's current point of attachment
to the
Internet.
The most important function needed to support such routing to mobile
nodes is the reliable Internet, and timely notification of a mobile node's
current location to those other nodes that need it. Correspondent
nodes communicating with a the mobile node need this location information
in order to correctly deliver their own packets may continue to a mobile node;
Mobile IPv6 allows correspondent communicate with
other nodes to learn and cache a mobile
node's location, and to use this cached information to route their
own packets directly (stationary or mobile) after moving to a mobile node at its current location. new subnet.
The
mobile node's "home agent", movement of a router on the mobile node's home
network, also needs this location information in order to forward
intercepted packets node away from the its home network subnet is thus
transparent to the mobile node, for
correspondent nodes that have not yet learned the mobile node's
location, transport and higher-layer protocols and indeed, applications.
The Mobile IPv6 protocol is just as suitable for correspondent nodes that do not even yet
know that the mobile mobility across
homogeneous media as for mobility across heterogeneous media. For
example, Mobile IPv6 facilitates node is currently away movement from home.
A mobile node's current location is represented one Ethernet
segment to another as a "care-of
address", well as it accommodates node movement from an IPv6 address assigned
Ethernet segment to a wireless LAN cell, as long as the mobile node (in addition
to its home IPv6 address) within the foreign network currently being
visited by the mobile node. The association between a mobile node's
home
IP address and its care-of address, along with the remaining
lifetime remains unchanged after such a movement.
One can think of that association, is known the Mobile IPv6 protocol as a "binding", and solving the mobile
node notifies other nodes about its current binding using a new
destination option called "macro"
mobility management problem. More "micro" mobility management
applications -- for example, handoff amongst wireless transceivers,
each of which covers only a Binding Update. very small geographic area, are possibly
more suited to other solutions. For example, as long as node
movement does not occur between link-level points of attachment on
different IPv6 correspondent nodes
then use subnets, link-layer mobility support offered by a Routing header to deliver subsequent packets
number of current wireless LAN products is likely to the mobile
node's care-of address. All IPv6 nodes offer faster
convergence and routers MUST be able to
cache mobile node bindings received in Binding Updates; this leads to
dramatic simplifications in the required protocols, compared lower overhead than Mobile IPv6. Extensions to the
methods required for IPv4.
In this document, "movement" is considered
Mobile IPv6 protocol are also possible to be a change in support a mobile
node's point more local,
hierarchical form of attachment to the Internet handoff, but such that it is no longer
link-level connected to the same IPv6 subnet (network prefix) as
it was previously. If a mobile node is not currently link-level
connected to its home IPv6 network, extensions are beyond the mobile node is said to be
"away from home". sope
of this document.
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1.1. Design Requirements
2. Terminology
2.1. General Terms
IP
Internet Protocol Version 6 (IPv6).
node
A device that implements IP.
router
A mobile node must continue that forwards IP packets not explicitly addressed to be able
itself.
host
Any node that is not a router.
link
A communication facility or medium over which nodes can
communicate at the link layer, such as an Ethernet (simple or
bridged). A link is the layer immediately below IP.
interface
A node's attachment to be addressed by a link.
network prefix
A bit string that consists of some number of initial bits of an
IP address.
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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2.2. Mobile IPv6 Terms
home address
An IP address assigned to a mobile node within its home
IPv6 address, and subnet.
The network prefix in a mobile node's home address is equal to be able
the network prefix of the home subnet.
home subnet
The IP subnet indicated by a mobile node's home address.
Standard IP routing mechanisms will deliver packets destined
for a mobile node's home address to communicate with other IPv6 nodes
using its home address, after changing subnet.
mobile node
A node that can change its link-level point of attachment from
one IPv6 IP subnet to another.
All messages used another, while still being addressable via its
home address.
movement
A change in a mobile node's point of attachment to update another node as the Internet
such that it is no longer link-level connected to the location of same IP
subnet as it was previously. If a mobile node must be authenticated in order is not currently
link-level connected to protect against remote
redirection attacks.
1.2. Goals
The number of administrative messages sent over its home subnet, the link by which
a mobile node is directly attached
said to the Internet should be
minimized, and the size of these messages should be kept as small
as "away from home".
correspondent node
A peer with which a mobile node is reasonably possible. This link communicating. The
correspondent node may often be a wireless link,
having a substantially lower bandwidth and higher error rate than
traditional wired networks, and many either mobile nodes are likely to
operate on limited battery power. By reducing or stationary.
foreign subnet
Any IP subnet other than the number and size
of administrative messages required for mobility support, network
resources and mobile node battery resources are conserved.
1.3. Assumptions
This protocol places no additional constraints node's home subnet.
home agent
A router on the assignment of
IPv6 addresses. That is, a mobile node's home subnet with which the mobile
node may acquire has registered its addresses
using stateless address autoconfiguration [12], or alternatively
using a stateful address configuration protocol such as DHCPv6 [3] or
PPPv6 [7].
This protocol assumes that any current care-of address. While the
mobile node will generally not change
its link-level point of attachment is away from one IPv6 subnet to another
more frequently than once per second.
This protocol assumes that IPv6 unicast home, the home agent intercepts
packets are routed based on the Destination Address in the packet's IPv6 header (and not, for
example, by source address).
1.4. Applicability
Mobile IPv6 is intended to enable nodes to move from one IPv6 home subnet destined to another. It is just as suitable for mobility across homogeneous
media as it is for mobility across heterogeneous media. That is,
Mobile IPv6 facilitates node movement from one Ethernet segment the mobile node's home
address, encapsulates them, and tunnels them to the mobile
node's registered care-of address.
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another as well as it accommodates node movement from an Ethernet
segment to
care-of address
An IP address associated with a wireless LAN, as long as the mobile node's IPv6 address
remains the same after such node while visiting
a movement.
One can think of Mobile IPv6 as solving foreign subnet, which uses the "macro" mobility
management problem. It is less well suited for more "micro" mobility
management applications -- for example, handoff amongst wireless
transceivers, each network prefix of which covers only that
foreign subnet. Among the multiple care-of addresses that a very small geographic
area. As long as
mobile node movement does not occur between link-level
points of attachment on different IPv6 subnets, link-layer mechanisms
for mobility management (i.e., link-layer handoff) may offer faster
convergence and far less overhead than Mobile IPv6.
1.5. Terminology
This document uses have at a time (e.g., with different network
prefixes), the following special terms:
Binding one registered with its home agent is called its
"primary" care-of address.
binding
The association of the home address of a mobile node with a
care-of address for that mobile node, along with the remaining
lifetime of that association.
Binding Cache
A cache, maintained by each IPv6 node,
2.3. Specification Language
In this document, several words are used to signify the requirements
of bindings for other
nodes. An entry in a node's binding cache for which the node specification. These words are often capitalized.
MUST
This word, or the adjective "REQUIRED", means that the
definition is serving as a home agent an absolute requirement of the specification.
MUST NOT
This phrase means that the definition is marked as an absolute
prohibition of the specification.
SHOULD
This word, or the adjective "RECOMMENDED", means that there may
exist valid reasons in particular circumstances to ignore a "home registration"
entry
particular item, but the full implications must be understood
and carefully weighed before choosing a different course.
SHOULD NOT be deleted by the node until the
expiration of its binding lifetime, whereas other Binding Cache
entries MAY be replaced at any time by any reasonable local
cache replacement policy. The Binding Cache is a conceptual
data structure used in this document, which
This phrase means that there may be implemented exist valid reasons in any manner consistent with
particular circumstances when the external particular behavior described
here, for example by being combined with the node's Destination
Cache as maintained through Neighbor Discovery [9].
Binding Update List
A list, maintained by each IPv6 mobile node, of the IPv6
address of each other node to which this node has sent a
Binding Update giving its binding, such that the lifetime of
the binding sent to that node has not yet expired. This is a
conceptual data structure used in this document, which may
acceptable or even useful, but the full implications should be
implemented in any manner consistent with
understood and the external case carefully weighed before implementing
any behavior described here. with this label.
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Care-of Address
An IPv6 address associated with a mobile node while visiting a
foreign network, which uses
MAY
This word, or the network prefix of adjective "OPTIONAL", means that foreign
network. Among an item
is truly optional. For example, one vendor may choose to
include the multiple care-of addresses that item because a mobile
node particular marketplace requires
it or because the vendor feels that it enhances the product,
while another vendor may have at a time (with different network prefixes), omit the
one registered with its home agent is called its "primary"
care-of address.
Correspondent Node
A peer with same item. An implementation
which does not include a mobile node is communicating. The
correspondent node may particular option MUST be either mobile or stationary.
Foreign Network
Any network other than prepared to
interoperate with another implementation which does include the mobile node's home network.
Home Address
An IPv6 address that is assigned for
option.
silently discard
The implementation discards the packet without further
processing, and without indicating an extended period of
time error to a mobile node. It remains unchanged regardless the sender. The
implementation SHOULD provide the capability of logging the
node's current link-level point
error, including the contents of attachment to the Internet.
Home Agent
A router on a mobile node's home network that, while discarded packet, and
SHOULD record the event in a statistics counter.
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3. Overview of Mobile IPv6 Operation
A mobile node is always addressable by its home address, whether it
is currently attached to its home subnet or is away from home. While
a mobile node is at home, intercepts packets on the home network
destined addressed to the mobile node's
home address, encapsulates them,
and tunnels them address are routed to it using conventional Internet routing
mechanisms in the mobile node's current care-of address.
The home agent maintains a registry of same way as if the current binding for node were never mobile. Since
the network prefix of a mobile nodes whose node's home address is on the home network routed
by equal to the home agent.
Home Network
A network, which may possibly be a virtual network, having a
network prefix matching that of a mobile node's its home address.
Standard IPv6 routing mechanisms will deliver subnet, packets destined
for addressed to it will be
routed to its home subnet.
While a mobile node's home address node is attached to the mobile node's home
network.
Link
A facility or medium over which nodes can communicate at the
link layer. A link underlies the network layer.
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Mobile Node
A node that can change its link-level point of attachment some foreign subnet away from
home, it is also addressable by one IPv6 subnet or more care-of addresses, in
addition to another, while still being addressable via its IPv6 home address.
Node A host or a router.
Tunnel
The path followed by care-of address is an IP address
associated with a packet mobile node only while it is encapsulated. visiting a particular
foreign subnet. The
model is that, while it is encapsulated, network prefix of a packet care-of address being used
by a mobile node is routed equal to the network prefix of the foreign
subnet to a knowledgeable decapsulating agent, which decapsulates the packet mobile node is link-level connected, and then correctly delivers it thus
packets addressed to its ultimate
destination.
Virtual Network
A network with no physical instantiation beyond this care-of address will be routed to the
mobile node's location away from home. The association between
a mobile node's home agent
(with address and care-of address is known as a physical network interface on another network). The
home agent generally advertises reachability
"binding" for the mobile node. A mobile node typically acquires its
care-of address through stateless [14] or stateful (e.g., DHCPv6 [3])
address autoconfiguration, according to the network
prefix methods of IPv6 Neighbor
Discovery [8], although other methods of acquiring a care-of address
are also possible.
While away from home, the virtual network using conventional routing
protocols.
1.6. Specification Language
In mobile node registers one of its binding
with a router in its home subnet, requesting this document, several words are used router to signify function
as the requirements
of "home agent" for the specification. These words are often capitalized.
MUST
This word, or mobile node. The care-of address in this
binding registered with its home agent is known as the adjective "required", means that 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
definition is an absolute requirement of mobile node's home address on the specification.
MUST NOT
This phrase means that home subnet, and tunnels
each intercepted packet to the definition mobile node's primary care-of address.
To tunnel each intercepted packet, the home agent encapsulates the
packet using IPv6 encapsulation [4], addressed to the mobile node's
primary care-of address.
Mobile IPv6 provides a mechanism for IPv6 nodes communicating with
a mobile node, to dynamically learn and cache the mobile node's
binding. When sending a packet to any IPv6 destination, a node
checks its cached bindings for an entry for the packet's destination
address. If a cached binding for this destination address is
found, the node uses an absolute
prohibition IPv6 Routing header [5] (instead of IPv6
encapsulation) to route the specification.
SHOULD
This word, or packet to the adjective "recommended", means that, mobile node through the
care-of address indicated in some
circumstances, valid reasons may exist to ignore this item, but binding. If, instead, the full implications must be understood and carefully weighed sending
node has no cached binding for this destination address, the node
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before choosing a different course. Unexpected results may
result otherwise.
MAY
This word, or
sends the adjective "optional", means that this item packet normally (with no Routing header), and the packet
is
one of an allowed set of alternatives. An implementation which
does not include this option MUST be prepared to interoperate
with another implementation which does include the option.
silently discard
The implementation discards the packet without further
processing, subsequently intercepted and without indicating an error to the sender. The
implementation SHOULD provide the capability of logging the
error, including tunneled by the contents mobile node's home
agent as described above. A node communicating with a mobile node is
referred to in this document as a "correspondent node" of the discarded packet, mobile
node.
A mobile node's home agent and
SHOULD record correspondent nodes learn and
cache the event in mobile node's binding through use of a statistics counter.
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destination options [5] defined for Mobile IPv6. Since an IPv6
Destination Options header containing one or more destination options
can appear in any IPv6 13 June 1996
2. Overview packet, any Mobile IPv6 option can be sent in
either of two ways:
- A Mobile IPv6 Operation
In addition to its (permanent) option can be included within any IPv6 home address, packet
carrying any payload such as TCP [11] or UDP [10].
- A Mobile IPv6 option can be sent as a mobile node
while away from home will have assigned separate IPv6 packet
containing no payload. In this case, the Next Header field
in the Destination Options header is set to its network interface(s)
a "primary care-of address" and possibly other "care-of addresses". the value 59, to
indicate "No Next Header" [5].
The following three new IPv6 destination options are defined for
Mobile IPv6:
Binding Update
A care-of address Binding Update is an IPv6 address assigned to used by a mobile node only
while visiting to notify a particular foreign network, typically acquired
through stateless [12] or stateful (e.g., DHCPv6 [3]) address
autoconfiguration. The decision about which manner of address
autoconfiguration to use is made according to the methods of IPv6
Neighbor Discovery [9].
Each time a mobile
correspondent node moves or its link-level point home agent of attachment from
one IPv6 subnet to another, it will configure its primary care-of
address at its new point of attachment, and will send a current binding.
The Binding Update containing that care-of address sent to its home agent. The
care-of address for a the mobile node registered with its node's home agent is
known
marked as the mobile node's "primary" care-of address, and the mobile
node may also have additional care-of addresses, one for each of the
network prefixes a "home registration". Any packet that it currently considers to be on-link. Each
time it changes its primary care-of address, includes a mobile node
Binding Update option MUST also sends
a include an IPv6 Authentication
header [1]. The Binding Update option is described in detail
in Section 4.1.
Binding Acknowledgement
A Binding Acknowledgement is used to each other (correspondent) node that may have acknowledge receipt of
a Binding Update, if an
out-of-date care-of address for acknowledgement was requested in the mobile node
Binding Update. Other Binding Updates MAY be acknowledged
but need not be. Any packet that includes a Binding
Acknowledgement option MUST also include an IPv6 Authentication
header [1]. The Binding Acknowledgement option is described in its
detail in Section 4.2.
Binding Cache. Request
A Binding Request is used to request a mobile node attached to the Internet can always be reached by
sending packets send a
Binding Update to this node, containing its home current binding.
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This option is not
present on its home network, any packet arriving there for it will be
intercepted there typically used by its home agent, which will tunnel the packet a correspondent node to
the
refresh a cached binding for a mobile node's current primary care-of address. node, when the lifetime
on this cached binding is close to expiration. The home agent
uses IPv6 encapsulation [5] Binding
Request option is described in detail in Section 4.3.
Extensions to tunnel the packet.
A correspondent node sending a packet checks its Binding Cache for
an entry for format of these options may be included after the Destination Address
fixed portion of the packet, and uses a
Routing header (instead option data specified in this document. The
presence of encapsulation) to route such extensions will be indicated by the packet to Option Length
field within the
destination mobile node's care-of address if a cached binding is
found. Otherwise, option. When the correspondent node sends Option Length is greater than the packet normally
(with no Routing header), and
length required for the packet is then intercepted and
tunneled by option specified here, the mobile node's home agent remaining octets
are interpreted as described above. When extensions. Currently, no extensions have been
defined.
This document describes the tunneled packet reaches Mobile IPv6 protocol in terms of the mobile node,
following two conceptual data structures used in the mobile node returns
a maintenance of
cached bindings:
Binding Update to the correspondent Cache
A cache, maintained by each IPv6 node, allowing it to cache the
mobile of bindings for other
nodes. An entry in a node's binding for future packets.
Since correspondent nodes cache bindings, it for which the node
is expected that
correspondent nodes usually will route packets directly to the mobile
node's care-of address, so that the serving as a home agent is rarely involved
with packet transmission to the mobile node. This is essential for
scalability and reliability, and for minimizing overall network load.
By caching the care-of address of marked as a mobile node, optimal routing of
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packets can SHOULD NOT be achieved between the correspondent node and the mobile
node. Routing packets directly to the mobile node's care-of address
also eliminates congestion at deleted by the mobile node's home agent and home
network. In addition, until the impact of
expiration of its binding lifetime, whereas other Binding Cache
entries MAY be replaced at any possible failure of the
home agent, the home network, or intervening networks leading to the
home network is drastically reduced, since these components are not
involved time by any reasonable local
cache replacement policy. The Binding Cache MAY be implemented
in any manner consistent with the delivery of most packets to the mobile node.
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in IPv6 13 June 1996
3. Message and Option Formats
3.1. this document, for example by being combined with the node's
Destination Cache as maintained through Neighbor Discovery [8].
Binding Update Option List
A list, maintained by each mobile node, recording information
for each Binding Update is a new IPv6 destination option, used sent by a this mobile
node to notify a correspondent node or its home agent node, for which
the Lifetime of its current
care-of address. As a destination option, it can appear in a
Destination Options header the binding sent in any IPv6 packet [6], and thus can be
included in any normal data packet or can be sent in a separate
packet containing no data. The that Update has not yet
expired. For each such Binding Update, the Binding Update contains List
records the mobile
node's care-of address, an identification IP address of the node to which the Update was
sent, the home address for which the Update (to sequence
Updates and to protect against attempts to replay it), was sent, and a the
remaining lifetime
for of the binding. The mobile node's IPv6 home address MUST Binding Update List
MAY be implemented in any manner consistent with the
source external
behavior described in this document.
When a mobile node configures a new care-of address of the packet containing the Binding Update, since
the option does not contain space and decides to separately represent
use this new address as its primary care-of address, the mobile
node's
node registers this new binding with its home address.
Binding Updates should be considered a form of routing updates;
handled incorrectly, they could be agent by sending
the home agent a source of security problems and
routing loops. Therefore, packets which include Binding Updates MUST
also include Update. The mobile node indicates
that an IPv6 Authentication header [1]; sequencing and replay
protection acknowledgement is then achieved by use of the Identification field in the needed for this Binding Update. Update and
continues to periodically retransmit it until acknowledged. The
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The
home agent acknowledges the Binding 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|A|H|L| Reserved | Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Identification +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Care-of Address +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Home Link-Local Address +
| (only present if L bit set) |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Option Type
16
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 Update option, this field
must be set to 28.
Acknowledge (A)
The Acknowledge (A) bit is set by the sending node to request returning a Binding
Acknowledgement message be returned upon receipt of the
Binding Update option.
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Home Registration (H)
The Home Registration (H) bit is set by the sending node to
request the receiving mobile node.
When a mobile node receives a packet tunneled to act as this node's it from its
home agent.
The Destination Address in the IPv6 header of agent, the packet
carrying this option MUST be mobile node assumes that of a router sharing the same
network prefix as original sending
correspondent node has no binding cache entry for the mobile node's home IPv6 address.
Home Link-Local Address Present (L)
The Home Link-Local Address Present (L) bit indicates the
presence of node,
since the Home Link-Local Address field in correspondent node would otherwise have sent the Binding
Update. This bit is set by packet
directly to the sending mobile node to request
the receiving using a Routing header. The mobile node to act as
thus returns a proxy (for participating in Binding Update to the Neighbor Discovery Protocol) correspondent node, allowing
it to cache the mobile node's binding for routing future packets.
Although the mobile node while may request an acknowledgement for this
Binding Update, it is
away need not, since subsequent packets from home. This bit MUST NOT be set unless the Home
Registration (H) bit is also set in the Binding Update.
Reserved
Sent as 0; ignored on reception.
Lifetime
16-bit unsigned integer. The number of seconds remaining
before the binding must
correspondent node will continue to be considered expired. A value of all
ones (0xffff) indicates infinity. A value of zero indicates
that intercepted and tunneled by
the mobile node's home agent, effectively causing any needed Binding Cache
Update retransmission.
A correspondent node with a binding cache entry for the a mobile node should be
deleted.
Identification
may refresh this binding, for example if the binding's lifetime
is near expiration, by sending a 64-bit number used to sequence Binding Updates and Request to match the mobile
node. Normally, a returned Binding Acknowledgement message with correspondent node will only refresh a binding
cache entry in this Binding
Update. The Identification field also serves to protect
against replay attacks for Binding Updates.
Care-of Address
The current care-of address of way if it is actively communicating with the
mobile node. When set equal node and has indications, such as an open TCP connection to
the home address of the mobile node, that it will continue this communication in the
future. When a mobile node receives a Binding Request, it replies by
returning a Binding Update
option instead indicates that any existing binding for to the
mobile node should be deleted; no binding for sending the Binding Request.
A mobile node
should may use more than one care-of address at the same time,
although only one care-of address may be created.
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Home Link-Local Address registered for it at its
home agent as its primary care-of address. The link-local address of mobile node's home
agent will tunnel all intercepted packets for the mobile node used by to its
registered primary care-of address, but the mobile node when will accept
packets that it was last attached to receives at any of its home network. This field
in the Binding Update is optional and is only present current care-of addresses.
Use of more than one care-of address by a mobile node may be useful,
for example, to improve smooth handoff when the
Home Link-Local Address (L) bit mobile node moves
from one wireless IP subnet to another. If each wireless subnet is set.
As with all IPv6 options,
connected to the highest-order three bits of Internet through a separate base station, such that
the Option
Type Field (16) of wireless transmission range from the Binding Update option specify two base stations overlap,
the following
properties mobile node may be able to remain link-level connected within
both subnets while in the area of overlap. In this case, the option:
- The highest-order two bits are 00: Any mobile
node receiving this
option that does not recognize could acquire a new care-of address in the Option Type MUST skip over
this option new subnet before
moving out of transmission range and continue processing link-level disconnecting from
the header.
- The third-highest-order bit is 0: old subnet. The Option Data does not
change en-route, mobile node may thus still accept packets at
its old care-of address while it works to update its home agent and thus, when an Authentication header is
present
correspondent nodes, notifying them of its new care-of address.
Since correspondent nodes cache bindings, it is expected that
correspondent nodes usually will route packets directly to the mobile
node's care-of address, so that the home agent is rarely involved
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with packet transmission to the packet, mobile node. This is essential for
scalability and reliability, and for minimizing overall network load.
By caching the entire Binding Update option MUST care-of address of a mobile node, optimal routing of
packets can be
included when computing or verifying achieved from the packet's authenticating
value.
Extensions correspondent node to the Binding Update option format may be included after mobile
node. Routing packets directly to the fixed portion of mobile node's care-of address
also eliminates congestion at the Binding Update option specified above.
The presence mobile node's home agent and home
subnet. In addition, the impact of of any possible failure of such extensions will be indicated by the Option
Length field. When
home agent, the Option Length is greater than 28 octets, home subnet, or intervening networks leading to the remaining octets
home subnet is reduced, since these nodes and links are interpreted as extensions. Currently no
extensions have been defined. not involved
in the delivery of most packets to the mobile node.
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3.2. ICMP
4. New IPv6 Destination Options
4.1. Binding Acknowledgement Message
A Update Option
The Binding Acknowledgement message Update destination option is an informational ICMP message used by a mobile node to acknowledge acceptance
notify a correspondent node or its home agent of a new care-of
address.
The Binding Update (Section 3.1)
option, if that Binding Update has the Acknowledge (A) bit set.
Upon receipt of a Binding Update requesting an acknowledgement, the
receiving node returns a Binding Acknowledgement message addressed to
the care-of address in the Binding Update.
If a mobile node fails to receive an acceptable Binding
Acknowledgement message within INITIAL_BINDACK_TIMEOUT seconds
after transmitting the Binding Update, it SHOULD retransmit the
Binding Update until a Binding Acknowledgement option is received. Such a
retransmitted Binding Update MUST use he same Identification value as
the original transmission. The retransmissions by the mobile node
MUST use an exponential back-off process, encoded in which timeout period
is doubled upon each retransmission until either the node receives
a Binding Acknowledgement message or the timeout period reaches the
value MAX_BINDACK_TIMEOUT.
The ICMP Binding Acknowledgement message has the following format: 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 | Code Option Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|A|H|L| Reserved | Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identification |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Care-of Address +
| |
+ +
| Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Identification +
| |
+ Home Link-Local Address +
| (only present if L bit set) |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Option Type
133
Code
192 ???
Option Length
8-bit unsigned integer indicating the disposition integer. Length of the
Binding Update. Values of option, in octets,
excluding the Code field less than 128
indicate that Option Type and Option Length fields. For the Binding Update was accepted by
current definition of the receiving
node. The following such values are currently defined:
0 Binding Update accepted option, this field
MUST be set to 24 if the Home Link-Local Address Present (L)
bit is not set, and MUST otherwise be set to 40.
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Values of
Acknowledge (A)
The Acknowledge (A) bit is set by the Code field greater than or equal sending node to 128 indicate
that request a
Binding Acknowledgement (Section 4.2) be returned upon receipt
of the Binding Update was rejected option.
Home Registration (H)
The Home Registration (H) bit is set by the sending node to
request the receiving node.
The following such 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 network
134 Identification field mismatch
135 Unknown node to act as this node's home agent address
Checksum agent.
The checksum Destination Address in the IP header of the message calculated packet carrying
this option MUST be that of a router sharing the same network
prefix as specified for ICMP
for IPv6 [4].
Identification
The acknowledgement Identification is derived from the Binding
Update option, for use by home address of the mobile node in matching the
acknowledgement with an outstanding Binding Update.
Up-to-date values binding.
Home Link-Local Address Present (L)
The Home Link-Local Address Present (L) bit indicates the
presence of the Code Home Link-Local Address field are to be specified in the most
recent "Assigned Numbers" [10].
Extensions to the Binding Acknowledgement message format may be
included after the fixed portion of the Binding Acknowledgement
message specified above. The presence of such extensions will be
indicated
Update. This bit is set by the ICMP message length, derived from sending node to request
the IPv6 Payload
Length field. When receiving node to act as a proxy (for participating in
the Option Length is greater than 16 octets, Neighbor Discovery Protocol) for the remaining octets are interpreted as extensions. Currently no
extensions have been defined.
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4. Requirements for IPv6 Nodes
Mobile IPv6 places some special requirements on the functions
provided by different IPv6 nodes. node while it is
away from home. This section itemizes those
requirements, identifying bit MUST NOT be set unless the functionality each requirement is
intended to support. Further details on this functionality Home
Registration (H) bit is
provided also set in the following sections.
Since any IPv6 node may at any time Binding Update.
Reserved
Sent as 0; ignored on reception.
Lifetime
16-bit unsigned integer. The number of seconds remaining
before the binding must be a correspondent considered expired. A value of a mobile
node, all IPv6 nodes MUST support
ones (0xffff) indicates infinity. A value of zero indicates
that the following requirements:
- Every IPv6 Binding Cache entry for the mobile node MUST should be able to process
deleted.
Identification
a received 32-bit number used by the receiving node to sequence Binding Update
option,
Updates, and by the sending node to return match a returned Binding
Acknowledgement message if
requested.
- Every IPv6 node MUST be able to maintain a with this Binding Cache Update.
Care-of Address
The care-of address of the
bindings received in accepted Binding Updates.
- Every IPv6 mobile node MUST be able to maintain Security Associations for use in IPv6 Authentication Headers [2, 1, 6]. An IPv6
node receiving a packet containing a Binding Update option
MUST verify, using the Authentication Header in the packet, this binding. When
set equal to the authenticity home address of the sender (the mobile node for which this
binding applies) before modifying its Binding Cache in response
to that node, the Binding
Update option.
Since option instead indicates that any IPv6 router may at any time have a Binding Cache entry
for a mobile node, all IPv6 router MUST support the following
requirement:
- Every IPv6 router MUST be able to use its Binding Cache in
forwarding packets; if the router has a Binding Cache entry for
the Destination Address of a packet it is forwarding, then the
router SHOULD encapsulate the packet and tunnel it to the care-of
address in the Binding Cache entry.
In order for a mobile node to correctly operate while away from
home, at least one IPv6 router in its home network must support
functioning as a home agent for the mobile node. All IPv6 routers
capable of serving as a home agent MUST support the following special
requirements:
- Every home agent MUST be able to maintain a registry of mobile
node bindings for those mobile nodes existing binding for which it is serving as
the home agent.
- Every home agent MUST be able to intercept packets (e.g., using
Neighbor Advertisements) on the local network addressed to
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a
the mobile node for which it holds a should be deleted; no binding in its registry
indicating that for the mobile
node is currently away from home.
- Every home agent MUST should be able to encapsulate such intercepted
packets created in order to tunnel them to the care-of this case.
Home Link-Local Address
The link-local address for of the mobile node indicated in used by the mobile
node when it was last attached to its binding.
- Every home agent MUST be able to issue Binding Acknowledgement
messages subnet. This field
in response to the Binding Updates received from a mobile
node.
- Every home agent MUST be able to maintain Security Associations
for Update is optional and is only present when the mobile nodes from which it will accept Binding Updates.
Finally, all IPv6 nodes capable
Home Link-Local Address (L) bit is set.
The home address of functioning as mobile nodes MUST
support the following requirements:
- Every IPv6 mobile node MUST be able to perform IPv6
decapsulation [5].
- Every IPv6 mobile node MUST support sending Binding Updates,
as specified in Sections 6.3, 6.4, and 6.5; and MUST be able
to receive and process Binding Acknowledgement messages, as
specified in Section 6.7.
- Every IPv6 mobile node MUST maintain a Binding Update List in
which it keeps track of which other IPv6 nodes it has sent a
Binding Update to, for which the Lifetime sent in that binding
has not yet expired.
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5. Binding Cache Management
The Binding Cache is indicated by
the central data structure Source Address field in Mobile IPv6.
All IPv6 nodes MUST support maintenance of a Binding Cache, and
MUST support processing of received Binding Updates. This section
describes the management aspects IP header of a Binding Cache common to all
nodes.
5.1. Receiving the packet containing
the Binding Updates
Upon receiving Update option.
Any packet that includes a Binding Update option in some packet, the receiving
node MUST validate the packet according to the following tests:
- The packet contains include an IP Authentication header and the
authentication is valid [1]. The IPv6
Authentication header is
assumed [1] in order to provide both authentication and integrity protection.
- protect against forged Binding
Updates.
The length three highest-order bits of the option specified in the Option Length field is
greater than or equal Type are encoded to 28 octets.
- The Identification field is valid.
Any
indicate specific processing of the option [5]. For the Binding
Update not satisfying all of option, these tests MUST be silently
ignored, although three bits are set to 110, indicating that the remainder of
data within the packet (i.e., other options,
extension headers, or payload) SHOULD be processed normally according option cannot change en-route to the packet's final
destination, and that any procedure defined for IPv6 node processing this option that part of does
not recognize the packet.
If Option Type must discard the Binding Update is valid according packet and, only if
the packet's Destination Address was not a multicast address, return
an ICMP Parameter Problem, Code 2, message to the tests above, then packet's Source
Address.
Extensions to the Binding Update is processed further as follows:
- If option format may be included after
the Lifetime specified in fixed portion of the Binding Update is nonzero and
the option specified Care-of Address differs from the Home Address,
this is a request to cache a binding for the mobile node.
Processing for this type above. The
presence of received Binding Update is described
in Section 5.2.
- If such extensions will be indicated by the Lifetime specified in Option Length
field. When the Binding Update Option Length is zero or greater than 24 octets if the
specified Care-of Home
Link-Local Address matches (L) bit is not set, or greater than 40 octets if
the Home Address, then this Link-Local Address (L) bit is
a request to delete set, the mobile node's binding. Processing for
this type of received Binding Update is described in Section 5.3.
5.2. Requests to Cache a Binding
If a node receives a valid Binding Update requesting it to cache a
binding for a mobile node, remaining octets
are interpreted as specified in Section 5.1, then the node
MUST examine the Home Registration (H) bit in the Binding Update extensions. Currently, no extensions have been
defined.
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to determine how to further process the
4.2. Binding Update. If the
Home Registration (H) bit is set, the Acknowledgement Option
The Binding Update is processed
according to the procedure specified in Section 7.1.
If the Home Registration (H) bit Acknowledgement destination option is not set, then the receiving
node SHOULD create a new entry in its Binding Cache for this mobile
node's Home Address (or update its existing Binding Cache Entry for
this Home Address) to record the Care-of Address as specified in the
Binding Update, and begin a timer used to delete this Binding Cache entry
after the expiration acknowledge
receipt of the Lifetime period specified in the Binding
Update.
5.3. Requests to Delete a Binding
If Update option (Section 4.1). When a node
receives a valid Binding Update requesting it addressed to delete
a binding for a mobile node, as specified in Section 5.1, then the
node MUST examine the Home Registration (H) bit itself, in which the Binding Update
to determine how to further process the Binding Update. If the
Home Registration (H)
Acknowledge (A) bit is set, the it MUST return a Binding Update Acknowledgement.
The Binding Acknowledgement option is processed
according to the procedure specified encoded in Section 7.2.
If the Home Registration (H) bit is not set, and if a node receives a
valid Binding Update requesting it to delete a binding for a mobile
node, type-length-value
(TLV) format as specified in Section 5.1, then it MUST delete any existing
entry in its Binding Cache for this mobile node's Home Address.
5.4. Sending Binding Acknowledgements
When any node receives a packet containing a Binding Update option,
it SHOULD return a Binding Acknowledgement message acknowledging
receipt 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Refresh | Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identification |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Option Type
193 ???
Option Length
8-bit unsigned integer. Length of the Binding Update. If the node accepts option, in octets,
excluding the Binding
Update Option Type and adds the binding contained in it to its Binding Cache, Option Length fields. For the
Code field in
current definition of the Binding Acknowledgement option, this
field MUST be set to a value 8.
Status
8-bit unsigned integer indicating the disposition of the
Binding Update. Values of the Status field less than 128; if the node rejects 128
indicate that the Binding Update and does not add was accepted by the binding contained in it to its receiving
node. The following such Status values are currently defined:
0 Binding Cache, Update accepted
Values of the Code Status field in
the Binding Acknowledgement MUST be set to a value greater than or equal to 128. Specific values for the Code field are described in
Section 3.2 and in the most recent "Assigned Numbers" [10].
The Destination Address in the IPv6 header for the Binding
Acknowledgement MUST be set to the Care-of Address copied from the
Binding Update option. This ensures 128
indicate that the Binding Acknowledgement
will be routed to the current location of the node sending the
Binding Update, whether Update was rejected by the receiving
node. The following such Status values are currently defined:
128 Reason unspecified
129 Poorly formed Binding Update was accepted or rejected.
130 Administratively prohibited
131 Insufficient resources
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5.5. Cache Replacement Policy
Any entry in a node's Binding Cache MUST be deleted after the
expiration
132 Home registration not supported
133 Not home subnet
134 Identification field mismatch
135 Unknown home agent address
Up-to-date values of the Lifetime Status field are to be specified in
the Binding Update from most recent "Assigned Numbers" [12].
Refresh
The recommended period at which the entry was created. Conceptually, a mobile node MUST maintain a separate
timer for each entry in its Binding Cache. When creating or updating should send
a new Binding Cache entry Update to this node in response order to a received Binding Update, "refresh" the
mobile node's binding in this node's binding cache, in case
the node sets fails and loses its cache state. The Refresh period
is determined by the timer for node sending the Binging Acknowledgement
(the node caching the binding). If this entry to node is serving as the specified Lifetime period.
When a Binding Cache entry's timer expires,
mobile node's home agent, the Refresh value may be set, for
example, based on whether the node MUST delete stores the
entry.
Each mobile node's Binding Cache will, by necessity, have a finite size.
A
binding in volatile storage or in nonvolatile storage. If the
node MAY use any reasonable local policy for managing sending the space
within its Binding Cache, except that any entry marked Acknowledgement is not serving as a "home
registration" (Section 7.1) SHOULD NOT be deleted from the cache
until
mobile node's home agent, the expiration of its lifetime period. When attempting to
add a new "home registration" entry in response Refresh period SHOULD be set
equal to Binding Update
with the Home Registration (H) bit set, if insufficient space exists
(or can be reclaimed) Lifetime period in the node's Binding Cache, the Acknowledgement;
even if this node MUST
reject the Binding Update and SHOULD return a Binding Acknowledgement
message loses this cache entry due to a failure of
the sending mobile node, in which packets from it can still reach the Code field is set to
131 (Insufficient resources). When otherwise attempting to add mobile node
through the mobile node's home agent, causing a new
entry to its Binding Cache, a
Update to this node MAY if needed choose to drop any
entry already in the Binding Cache other than a "home registration"
entry, in order allow it to make space for the new recreate this cache entry. For example, a
"least-recently used" (LRU) strategy
Lifetime
The granted lifetime for cache entry replacement is
likely to work well.
If a packet is sent by a which this node will attempt to a destination for which it has
dropped retain
the cache entry from for this mobile node in its Binding Cache, binding cache. If the packet will be
routed normally, leading to
node sending the Binding Acknowledgement is serving as the
mobile node's home network, where it agent, the Lifetime period also indicates
the period for which this node will be intercepted by continue this service; if
the mobile node's node requires home agent and tunneled to service from this node
beyond this period, the mobile node's current primary care-of address. As when node MUST send a new Binding
Cache entry is initially created, this indirect routing
Update to it before the mobile
node will result in the mobile node sending a Binding Update to this
sending node, allowing it to add expiration of this entry again to its Binding
Cache.
5.6. Receiving ICMP Error Messages
When a correspondent node sends a packet period to a mobile node, if extend the
lifetime.
Identification
The acknowledgement Identification is copied from the
correspondent node has a Binding Cache entry
Update option, for use by the destination mobile node's address (its home address), then the correspondent node
uses a Routing header to deliver the packet to the mobile node's
care-of address, and then to in matching the mobile node's home address.
acknowledgement with an outstanding Binding Update.
Any
ICMP error message caused by the packet on its way to the mobile node
will be returned normally that includes a Binding Acknowledgement option MUST
include an IPv6 Authentication header [1] in order to the correspondent node. protect against
forged Binding Acknowledgements.
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On the other hand, if
If the correspondent node has no returning the Binding Cache
entry Acknowledgement accepted the
Binding Update for which the mobile node, Acknowledgement is being returned (the
value of the packet will be routed to Status field in the mobile
node's home network, where it Acknowledgement is less than 128),
this node will be intercepted by have an entry for the mobile
node's home agent, encapsulated, node in its Binding
Cache, and tunneled to MUST use this entry (which includes the mobile node's care-of address. Similarly, if a address
received in the Binding Update) in sending the packet for a mobile node arrives
at containing the
Binding Acknowledgement to the mobile node's previous default router (e.g., node. The details of sending
this packet to the mobile node
moved after the packet was sent), the router will encapsulate and
tunnel are the same as for sending any packet
to the a mobile node's new care-of address (if it has node using a Binding Cache entry for the mobile node). Any ICMP error message
caused by entry, and are described in
Section 6.7. The packet is sent using a Routing header, routing the
packet on its way to the mobile node while through its care-of address recorded in the
tunnel, will be returned to
Binding Cache entry.
If the node that encapsulated returning the packet Binding Acknowledgement instead
rejected the Binding Update (the home agent or value of the previous default router, respectively). By Status field in the definition of IPv6 encapsulation [5], however,
Acknowledgement is greater than or equal to 128), this encapsulating node MUST relay certain ICMP error messages back to the original
sender of
similarly use a Routing header in sending the packet (the correspondent node).
Thus, whether containing the correspondent node has a
Binding Acknowledgement, as described in Section 6.7, but MUST NOT
use its Binding Cache entry
for in forming the destination mobile node IP header or not, Routing header
in this packet. Rather, the correspondent node
will receive any meaningful ICMP error message that is caused care-of address used by
its packet on its way to the mobile node. If the correspondent this node receives an ICMP Host Unreachable or Network Unreachable
error message after in
sending a the packet to a mobile node using its
cached containing the Binding Acknowledgement MUST be
copied from the care-of address, address received in the correspondent rejected Binding
Update; this node SHOULD delete MUST NOT modify its Binding Cache entry for in response
to receiving this mobile node. If rejected Binding Update and MUST ignore its
Binding Cache in sending the correspondent node
subsequently transmits another packet to the mobile node, in which it returns this Binding
Acknowledgement. The packet is sent using a Routing header, routing
the packet
will be routed to the mobile node's home network, intercepted by Source Address of the
mobile node's home agent, and tunneled to rejected Binding Update
through the mobile node's care-of address using IPv6 encapsulation. indicated in the Binding Update.
The mobile node will then return a three highest-order bits of the Option Type are encoded to
indicate specific processing of the option [5]. For the Binding Update
Acknowledgement option, these three bits are set to 110, indicating
that the correspondent node, allowing it data within the option cannot change en-route to recreate the
packet's final destination, and 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
(correct)
multicast address, return an ICMP Parameter Problem, Code 2, message
to the packet's Source Address.
Extensions to the Binding Cache entry for Acknowledgement option format may be
included after the mobile node. fixed portion of the Binding Acknowledgement
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. Mobile Node Considerations
6.1. Movement Detection
A
4.3. Binding Request Option
The Binding Request destination option is used to request a mobile
node's binding from the mobile node. When a mobile node MAY use any combination of mechanisms available to receives
a packet containing a Binding Request option, it SHOULD return a
Binding Update (Section 4.1) to detect when its link-level point of attachment has moved
from one IPv6 subnet to another. that node.
The primary movement detection
mechanism for Mobile IPv6 defined here uses the facilities 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
194 ???
Option Length
8-bit unsigned integer. Length of
IPv6 Neighbor Discovery, including Router Discovery the option, in octets,
excluding the Option Type and Neighbor
Unreachability Detection. The description here is based on Option Length fields. For the
conceptual model
current definition of the organization and data structures defined by
Neighbor Discovery [9].
Mobile nodes SHOULD use Router Discovery Binding Acknowledgement option, this
field MUST be set to discover new routers and
on-link network prefixes; a mobile node MAY send Router Solicitation
messages, or MAY wait for unsolicited (periodic) Router Advertisement
messages, as specified for Router Discovery [9]. Based on received
Router Advertisement messages, a mobile node (in 0.
The three highest-order bits of 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 network prefix,
that it currently considers Option Type are encoded to be on-link. Each entry in
indicate specific processing of the option [5]. For the Binding
Request option, these
lists has an associated invalidation timer value (extracted from three bits are set to 110, indicating that the
Advertisement) used
data within the option cannot change en-route 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, packet's final
destination, and one network
prefix advertised by that router from its Prefix List 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 use as the network prefix in its primary care-of address. A mobile node
MAY also have associated additional care-of addresses, using other
network prefixes from its Prefix List. packet's Source
Address.
Extensions to the Binding Request option format may be included after
the fixed portion of the Binding Request option specified above.
The method presence of such extensions will be indicated by which a mobile
node selects and forms a care-of address from the available network
prefixes Option
Length field. When the Option Length is described in Section 6.2. The mobile node registers
its primary care-of address with its home agent, greater than 0 octets,
the remaining octets are interpreted as described in
Section 6.3.
While away from home extensions. Currently, no
extensions have been defined.
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5. Requirements for IPv6 Nodes
Mobile IPv6 places some router as its default router,
it special requirements on the functions
provided by different IPv6 nodes. This section summarizes those
requirements, identifying the functionality each requirement is important for a mobile node
intended to support. Further details on this functionality is
provided in the following sections.
Since any IPv6 node may at any time be able to quickly detect when
that router becomes unreachable, so that it can switch a correspondent node of a
mobile node, the following requirements pertain to all IPv6 nodes:
- Every IPv6 node SHOULD be able to process a new
default router received Binding
Update option, and to return a new primary care-of address. Since some
links (notably wireless) do not necessarily work equally well Binding Acknowledgement message if
requested.
- Every IPv6 node SHOULD be able to maintain a Binding Cache of the
bindings received in
both directions, it is likewise important accepted Binding Updates.
In order for the a mobile node to
detect when it becomes unreachable to its default router, so that any
correspondent nodes attempting to communicate with operate correctly while away from
home, at least one IPv6 router in the mobile node
can still reach it.
To detect when its default router becomes unreachable, node's home subnet must
function as a mobile
node SHOULD use Neighbor Unreachability Detection. As specified
in Neighbor Discovery [9], while home agent for the mobile node is actively
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requirements pertain to all IPv6 13 June 1996
sending packets routers capable of serving as a home
agent:
- Every home agent MUST be able to (or through) its default router, the maintain a registry of mobile
node
can detect that bindings, recording each mobile node's primary care-of
address, for those mobile nodes for which it is serving as the router has become unreachable either through
indications from upper layer protocols
home agent.
- Every home agent MUST be able to intercept packets (using proxy
Neighbor Discovery) on the local subnet addressed to a mobile
node that a
connection is not making "forward progress" (e.g., TCP timing out
waiting for an acknowledgement after a number of retransmissions),
or through which it is currently serving as the failure home agent while
that mobile node is away from home.
- Every home agent MUST be able to receive a Neighbor Advertisement messages
form its default router encapsulate such intercepted
packets in response to retransmitted explicit
Neighbor Solicitation messages order to it. No exceptions tunnel them to Neighbor
Unreachability Detection are necessary the primary care-of address
for this aspect of movement
detection in Mobile IPv6.
For a the mobile node indicated in its binding.
- Every home agent MUST be able to detect when it has become unreachable return Binding Acknowledgements
in response to its
default router, however, Binding Updates received from a mobile node.
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Finally, the following requirements pertain all IPv6 nodes capable of
functioning as mobile nodes:
- Every IPv6 mobile node cannot efficiently rely on
Neighbor Unreachability Detection alone, since the network overhead
would MUST be prohibitively high in many cases for a able to perform IPv6
decapsulation [4].
- Every IPv6 mobile node to
continually probe its default router with Neighbor Solicitation
messages even when it is not otherwise actively MUST support sending packets Binding Updates, as
specified in Sections 8.3, 8.4, and 8.5; and MUST be able to
it. Instead, a
receive and process Binding Acknowledgements, as specified in
Section 8.8.
- Every IPv6 mobile node SHOULD consider receipt of any IPv6
packets from its current default router as an indication that MUST maintain a Binding Update List in
which it is
still reachable from the router. Both packets from records the router's IPv6
address and (IPv6) packets from its link-layer IP address (e.g., those
forwarded but not originated by the router) SHOULD be considered.
Since the router SHOULD be sending periodic multicast Router
Advertisement messages, the mobile node will have frequent
opportunity to check if it is still reachable to its default router,
even in the absence of each other packets node to which it from the router. On some
types of network interfaces,
has sent a Binding Update, for which the mobile node MAY also supplement
this by setting its network interface into "promiscuous" receive
mode, so Lifetime sent in that is able to receive all packets on the link, including
those
binding has not link-level addressed to it. The mobile yet expired.
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6. Correspondent Node Operation
A correspondent node will then
be able to detect is any packets sent by the router, node communicating with a mobile node.
The correspondent node, itself, may be fixed or mobile, and may
possibly also be functioning as a home agent for Mobile IPv6. The
procedures in order to this section thus apply to
detect reachability from all IPv6 nodes.
6.1. Receiving Binding Updates
Upon receiving a Binding Update option in some packet, the router. This may be useful on very low
bandwidth (e.g., wireless) links, but its use receiving
node MUST be configurable on validate the mobile node.
If packet according to the above means do not provide indication that following tests:
- The packet contains an IP Authentication header and the mobile node
authentication is still reachable from its current default router (i.e., the
mobile node receives no packets form valid [1]. The Authentication header is
assumed to provide both authentication and integrity protection.
- The Option Length field in the router option is greater than or equal to
24 octets if the Home Link-Local Address (L) bit is not set, or
greater or equal to 40 octets if the Home Link-Local Address (L)
bit is set.
- The Identification field is valid.
Any Binding Update 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 a period that part of
time), the packet.
If the Binding Update is valid according to the tests above, then the mobile node SHOULD actively probe
Binding Update is processed further as follows:
- If the router with
Neighbor Solicitation messages, even if it Lifetime specified in the Binding Update is nonzero and
the specified Care-of Address is not otherwise actively
sending packets equal to the router. If it receives a solicited Neighbor
Advertisement message Source Address
in response from the router, IP header of the packet carrying the Binding Update,
then this is a request to cache a binding for the mobile node can deduce that it is still reachable. It is expected that
(the home address of the mobile node will is specified by the Source
Address field in most cases be able to determine its reachability
from the router by listening packet's IP header). Processing for packets from the router as this
type of received Binding Update is described
above, and thus, such extra Neighbor Unreachability Detection probes
should rarely be necessary.
Johnson in Section 6.2.
- If the Lifetime specified in the Binding Update is zero or the
specified Care-of Address matches the Source Address field in the
IP header of the packet carrying the Binding Update, then this is
a request to delete the mobile node's binding (as above, the home
address of the mobile node is specified by the Source Address
field in the packet's IP header). Processing for this type of
received Binding Update is described in Section 6.3.
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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,
6.2. Requests to Cache a Binding
If a mobile node MUST NOT assume that all link-layer
mobility indications from lower layers indicate receives a movement of the
mobile node's link-layer connection valid Binding Update requesting it to cache a
binding for a new IPv6 subnet, such that
the mobile node, as specified in Section 6.1, then the node would need
MUST examine the Home Registration (H) bit in the Binding Update
to switch determine how to a new default router and
primary care-of address. Upon lower-layer indication of link-layer
mobility, further process the mobile Binding Update. If the
Home Registration (H) bit is set, the Binding Update is processed
according to the procedure specified in Section 7.1.
If the Home Registration (H) bit is not set, then the receiving node
SHOULD send Router Solicitation messages
to determine if new routers (and create a new on-link network prefixes) are
present on entry in its new link.
Such lower-layer information might also be useful to a Binding Cache for this mobile node in
deciding to switch
(or update its primary care-of existing Binding Cache entry for this mobile node, if
such an entry already exists). The home address to one of the other
care-of addresses it has formed from the on-link network prefixes
currently available through different default 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 taken from the available default routers to decide when to
switch to a Source Address field in the packet's IP header.
The new primary care-of Binding Cache entry records the association between this
address using that default router
rather than its current default router (and current primary care-of
address). Even though and the mobile node's current default router may
still be reachable Care-of Address specified in terms of Neighbor Unreachability Detection, the
mobile Binding Update.
The node MAY use such lower-layer information must also begin a timer to determine that
switching delete this Binding Cache entry
after the expiration of the Lifetime period specified in the Binding
Update.
6.3. Requests to Delete a new default router would provide Binding
If a better connection.
6.2. Forming New Care-of Addresses
After detecting that its link-layer point of attachment has moved
from one IPv6 subnet to another (i.e., its current default router
has become unreachable and node receives a valid Binding Update requesting it has discovered to delete
a new default router), binding for a mobile node, as specified in Section 6.1, then the
node SHOULD form a new primary care-of address using one of MUST examine the on-link network prefixes advertised by Home Registration (H) bit in the new router. A mobile Binding Update
to determine how to further process the Binding Update. If the
Home Registration (H) bit is set, the Binding Update is processed
according to the procedure specified in Section 7.2.
If the Home Registration (H) bit is not set, then the receiving node MAY form a new primary care-of address at any time, except
that it
MUST NOT do so too frequently (more often than once per
MAX_UPDATE_RATE seconds).
In addition, after discovering a new on-link network prefix, a delete any existing entry in its Binding Cache for this mobile node MAY form a new (non-primary) care-of
node. The home address using that
network prefix, even when it has not switched to a new default
router. A of the mobile node can have only one primary care-of address
at is taken from the Source
Address field in the packet's IP header.
6.4. Sending Binding Acknowledgements
When any node receives a time (registered with its home agent), but it MAY have an
additional care-of address for each network prefix on its current
link. Furthermore, since packet containing a wireless network interface may actually
allow Binding Update option
in which the Acknowledge (A) bit is set, it SHOULD return a mobile Binding
Acknowledgement message acknowledging receipt of the Binding
Update. If the node accepts the Binding Update and adds the binding
contained in it to its Binding Cache, the Status field in the
Binding Acknowledgement MUST be reachable on more than one link at set to a time
(i.e., within wireless transmitter range of routers on more value less than one
separate link), a mobile 128; if
the node MAY have care-of addresses on more rejects the Binding Update and does not add the binding
contained in it to its Binding Cache, the Status field in the Binding
Acknowledgement MUST be set to a value greater than or equal to 128.
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one link at a time. For more information on using more than one
care-of address at a time, see
Specific values for the Status field are described in Section 6.8. 4.2 and
in the most recent "Assigned Numbers" [12].
As described in Section 2, 4.2, the packet in which the Binding
Acknowledgement is returned MUST include an IPv6 Authentication
header [1] in order to form protect against forged Binding
Acknowledgements, and the packet MUST be sent using a new Routing
header through the care-of address,
a mobile node MAY use either stateless [12] or stateful (e.g.,
DHCPv6 [3]) address autoconfiguration. If a mobile node needs contained in the Binding Update
being acknowledged. This ensures that the Binding Acknowledgement
will be routed to
send packets as part of the method current location of address autoconfiguration, it
MUST use an IPv6 link-local address rather than its own IPv6 home
address as the Source Address.
In some cases, a mobile node may already know sending the
Binding Update, whether the Binding Update was accepted or rejected.
6.5. Cache Replacement Policy
Any entry in a (constant) IPv6
address that has been assigned to it for its use while visiting this
network. For example, it may node's Binding Cache MUST be statically configured with an IPv6
address assigned by deleted after the system administrator
expiration of the new network. If
so, rather than using address autoconfiguration to form a new care-of
address using this network prefix, Lifetime specified in the mobile node SHOULD use its own
pre-assigned address as its care-of address on this network.
6.3. Sending Binding Updates to Update from which
the Home Agent
After changing its primary care-of address as described in
Sections 6.1 and 6.2, entry was created or was last updated. Conceptually, a mobile node SHOULD register its new primary
care-of address with its home agent. To do so, the mobile node sends
maintains a packet to separate timer for each entry in its home agent containing a Binding Update option with
the Acknowledge (A) bit set, requesting the home agent to return Cache. When
creating or updating a Binding Acknowledgement message Cache entry in response to this a received
and accepted Binding Update.
As described in Section 3.2, Update, the mobile node SHOULD retransmit sets the timer for this
Binding Update entry
to its home agent until it receives the specified Lifetime period. When a matching Binding
Acknowledgement message. Once reaching a retransmission timeout
period of MAX_BINDACK_TIMEOUT, Cache entry's timer
expires, the mobile node SHOULD continue
to periodically retransmit deletes the entry.
Each node's Binding Update at this rate until
acknowledged.
It is useful for Cache will, by necessity, have a mobile finite size.
A node to MAY use any reasonable local policy for managing the space
within its Binding Cache, except that any entry marked as a "home
registration" (Section 7.1) MUST NOT be able deleted from the cache until
the expiration of its lifetime period. When attempting to add a new
"home registration" entry in response to send a Binding Update
its home agent without explicitly knowing the home agent's address.
For example, since with the mobile node was last at home, it may have
become necessary to replace
Home Registration (H) bit set, if insufficient space exists (or can
be reclaimed) in the node's Binding Cache, the node serving as its home agent due MUST reject the
Binding Update and SHOULD return a Binding Acknowledgement message
to the failure of sending mobile node, in which the original node or due Status field is set to reconfiguration of the
home network. It thus may not always be possible or convenient for 131
(Insufficient resources). When otherwise attempting to add a new
entry to its Binding Cache, a
mobile node MAY, if needed, choose to know the exact address of drop any
entry already in its own home agent.
Mobile nodes can dynamically discover Binding Cache, other than a "home registration"
entry, in order to make space for the address of new entry. For example, a home agent
"least-recently used" (LRU) strategy for cache entry replacement is
likely to work well.
If a packet is sent by sending a node to a destination for which it has
dropped the cache entry from its Binding Update Cache, the packet will be
routed normally, leading to the anycast address on their mobile node's home
network. Each router on subnet. There,
the home network which receives this Binding
Update MUST reject packet will be intercepted by the Binding Update mobile node's home agent and include its address in
tunneled to the mobile node's current primary care-of address. As
when a Binding Acknowledgement message indicating Cache entry is initially created, this indirect
routing to the rejection. The mobile node is assumed to know a proper anycast address on through its home network agent will result in the
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before making use of this method for determining a particular home
agent's address.
6.4. Sending Binding Updates to Correspondent Nodes
A 26 November 1996
mobile node MAY also include sending a Binding Update in any normal data
packet sent to this sending node, allowing
this node to add an entry again for this destination to its Binding
Cache.
6.6. Receiving ICMP Error Messages
When a correspondent node. For each correspondent node sends a packet to which it a mobile node, if the
correspondent node has sent a Binding Update, Cache entry for the destination
mobile node MUST keep
information to determine whether or not node's address (its home address), then the correspondent
node has
been sent uses a fresh Binding Update since Routing header to deliver the last time packet to the mobile node
switched to a new primary
through the care-of address. When a address recorded in the Binding Cache entry. Any
ICMP error message caused by the packet is on its way to the mobile node
will be
sent returned normally to a the correspondent node.
On the other hand, if the correspondent node that has not been sent a fresh no Binding
Update, Cache
entry for the mobile node SHOULD include the Binding Update within node, the
packet. Thus, correspondent nodes are generally kept updated and
can send almost all data packets directly packet will be routed to the mobile node using
node's home subnet, where it will be intercepted by the mobile node's current binding. Such Binding Updates are not
generally required
home agent, encapsulated, and tunneled to be acknowledged; however, if the mobile node
wants node's care-of
address. Any ICMP error message caused by the packet on its way to be sure, an acknowledgement can be requested, although in
this case,
the mobile node SHOULD NOT continue while in the tunnel, will be returned to retransmit the
Binding Update once the retransmission timeout period has reached
MAX_BINDACK_TIMEOUT.
A mobile node MAY also send a Binding Update in any otherwise empty
packet, whenever the mobile node wishes to update a correspondent
node as to its current binding. This is normally done only if the mobile suspects that its
node's home agent is not operational or is
too far away, a correspondent node is not sending (the source of the traffic tunnel) By the definition of
IPv6 encapsulation [4], this encapsulating node MUST relay certain
ICMP error messages back to the proper care-of address, or there original sender of the packet, which
in this case is an immediate need for the correspondent node.
Likewise, if a packet for a mobile node to obtain arrives at the mobile node's
previous default router (e.g., the binding. A mobile node can detect
that a correspondent node is not sending packets to moved after the proper
care-of address because in that case packet
was sent), the packets arrive at router will encapsulate and tunnel the packet to the
mobile node's new care-of address by encapsulation instead by inclusion in (if it has a
routing header within Binding Cache entry
for the packet.
A mobile node MAY choose node). As above, any ICMP error message caused by the
packet while in this tunnel will be returned to keep its location private from the previous default
router (the source of the tunnel), which MUST relay certain
correspondent nodes, and thus need not send new Binding Updates ICMP
error messages back to
those correspondents. A mobile the correspondent node MAY also send a Binding Update
to such [4].
Thus, in all cases, any meaningful ICMP error messages caused by
packets from a correspondent node to instruct it to delete any existing
binding for the a mobile node from its Binding Cache, as described in
Section 3.1. No other IPv6 nodes are authorized will be returned
to the correspondent node. If the correspondent node receives
persistent ICMP Host Unreachable or Network Unreachable error
messages after sending packets to send Binding
Updates on behalf of a mobile node.
6.5. Sending node based on an entry in
its Binding Updates Cache, the correspondent node SHOULD delete this Binding
Cache entry. If the correspondent node subsequently transmits
another packet to the Previous Default Router
After switching mobile node, the packet will be routed to a new default router (and thus also changing
its primary the
mobile node's home subnet, intercepted by the mobile node's home
agent, and tunneled to the mobile node's care-of address), a address using IPv6
encapsulation. The mobile node SHOULD send will then return a Binding Update to
the correspondent node, allowing it to recreate a (correct) Binding
Cache entry for the mobile node.
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Update message
6.7. Sending Packets to a Mobile Node
Before sending any packet, the sending node SHOULD examine its previous default router, giving its new care-of
address.
Binding Cache for an entry for the destination address to which the
packet is being sent. If it sends such the sending node has a Binding Update, Cache entry
for this address, the mobile sending node MUST set SHOULD use a Routing header to
route the Home Address field packet to its old primary care-of address (that it
used while using this default router), and set mobile node (the destination node) through
the Care-of Address
field to its new primary care-of address. Note that the previous
router does not necessarily know the mobile node's home address as
part of this sequence recorded in that Binding Cache entry. For
example, assuming use of events.
The a Type 0 Routing header [5], if no other use
of a Routing header is involved in the routing of this packet, the
mobile node's previous default router then, node sets the following fields in effect,
temporarily act the packet's IP header and
Routing header as a home agent for indicated below:
- The Destination Address in the mobile node's old primary
care-of address. If any subsequent packets arrive at this previous
router for forwarding packet's IP header is set to the
mobile node's old primary care-of
address, address copied from the router SHOULD encapsulate each and tunnel it Binding Cache
entry.
- The Routing header is initialized to contain a single route
segment, with an Address of the mobile node at its new primary care-of address. Moreover, node's home address (the
original destination address to which the
previous router should issue Neighbor Advertisement packets for packet was being sent).
Following the
previous care-of address, so that on-link neighbors definition of a Type 0 Routing header [5], this packet
will send packets
destined routed to the mobile node's old primary care-of address address, where it will be
delivered to the
previous router for encapsulation and tunneling to its new care-of
address.
6.6. Rate Limiting for Sending Binding Updates
A mobile node MUST NOT send Binding Update messages more often than
once per MAX_UPDATE_RATE seconds to any correspondent node. After
sending 5 consecutive Binding Updates to a particular correspondent (the mobile node with has associated the same
care-of address, the mobile node SHOULD reduce address with its
rate network interface). Normal processing of sending Binding Updates to that correspondent node, to
the
rate of SLOW_UPDATE_RATE per second. The Routing header by the mobile node MAY continue
to send Binding Updates at will then proceed as follows:
- The mobile node swaps the slower rate indefinitely, Destination Address in hopes
that the correspondent node will finally be able to process a Binding
Update packet's IP
header and begin the Address specified in the Routing header. This
results in the packet's IP Destination Address being set to route its packets directly the
mobile node's home address.
- The mobile node then resubmits the packet to its IPv6 module for
further processing. Since the mobile node at recognizes its own
home address as one if its current primary care-of address.
6.7. Receiving IP addresses, the packet is
processed further within the mobile node, in the same way then as
if the mobile node was at home.
If, instead, the sending node has no Binding Acknowledgements
Upon receiving a Cache entry for the
destination address to which the packet carrying is being sent, the sending
node simply sends the packet normally, with no Routing header. If
the destination node is not a Binding Acknowledgement message, mobile node (or is a mobile node MUST validate that
is currently at home), the packet according will be delivered directly to the following
tests:
- The packet contains an IP Authentication header this
node and processed normally by it. If, however, the
authentication destination node
is valid [1]. The Authentication header a mobile node that is
assumed to provide both authentication currently away from home, the packet will
be intercepted by the mobile node's home agent and integrity protection.
- tunneled (using
IPv6 encapsulation [4]) to the mobile node's current primary care-of
address, as described in Section 7.3. The ICMP Checksum is valid. mobile node will then send
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- The length of
a Binding Update to the ICMP message (derived from sending node, as described in Section 8.4,
allowing the IPv6 Payload
Length field) is greater than or equal sending node to 16 octets.
- The Identification field is valid.
Any create a Binding Acknowledgement not satisfying all Cache entry for its use
in sending subsequent packets to this mobile node.
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7. Home Agent Operation
7.1. Primary Care-of Address Registration
General processing of these tests MUST a received Binding Update that requests a
binding to be
silently discarded.
If cached, is described in Section 6.2. However, if the Binding Acknowledgement
Home Registration (H) bit is valid, set in the mobile Binding Update, then the
receiving node MUST examine process the Code field Binding Update as follows:
- If specified in this
section, rather than following the Code field indicates that general procedure specified in
Section 6.2.
To begin processing the Binding Update was accepted
(the Code field Update, the home agent MUST perform
the following sequence of tests:
- If the node is less than 128), not a router that implements home agent
functionality, then the mobile node MUST
update reject the corresponding entry in its Binding Update List and
SHOULD return a Binding Acknowledgement message to
indicate that the Binding Update has been acknowledged. The mobile node SHOULD thus stop retransmitting
node, in which the Binding Update. Status field is set to 132 (Home registration
not supported).
- If Else, if the Code field indicates that home address for the binding in the Binding Update was not
accepted
(the Code field Source Address in the packet's IP header) is greater than or equal not an on-link
IPv6 address with respect to 128), the home agent's current Prefix
List, then the mobile node home agent MUST delete reject the corresponding Binding Update List
entry. Optionally, and
SHOULD return a Binding Acknowledgement message to the mobile node MAY take steps to correct
node, in which the
cause of Status field is set to 133 (Not home subnet).
- Else, if the error and retransmit home agent chooses to reject the Binding Update, subject Update for
any other reason (e.g., insufficient resources to
the rate limiting restriction specified in Section 6.6.
6.8. Using Multiple Care-of Addresses
As described in Section 6.2, a serve another
mobile node MAY have more than
one care-of address at as a time. Particularly in home agent), then the case of many
wireless networks, home agent SHOULD return
a mobile node effectively may be reachable through
multiple link-level points of attachment at Binding Acknowledgement message to the same time (e.g.,
with overlapping wireless cells), on which different on-link network
prefixes may exist. A mobile node SHOULD select a primary care-of
address from among those care-of addresses node, in which
the Status field is set to an appropriate value to indicate the
reason for the rejection.
If the home agent does not reject the Binding Update as described
above, then it has formed using any
of these network prefixes, based on becomes the movement detection mechanism
in use (Section 6.1). When home agent for the mobile node selects a node. The new primary
care-of address, it MUST register it with its
home agent through (the receiving node) MUST then create a
Binding Update message with new entry or
update the Acknowledge (A) bit set, existing entry in its Binding Cache for this mobile node's
home address, as described in Section 6.3.
To assist in smooth handoffs, a mobile node SHOULD retain its
previous primary care-of address 6.2. In addition, the home
agent MUST mark this Binding Cache entry as a 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 "home registration"
to indicate that
link. the node is serving as a home agent for this
binding. Binding Cache entries marked as a "home registration" MUST
be excluded from the normal cache replacement policy used for the
Binding Cache (Section 6.5) and MUST NOT be removed from the Binding
Cache until the expiration of the Lifetime period.
If the previous primary care-of address home agent was allocated using
stateful address autoconfiguration [3], the not already serving as a home agent for this
mobile node may (the home agent did not wish already have a Binding Cache
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to release the
entry for this address immediately upon switching to marked as a new primary
care-of address. The stateful address autoconfiguration server
will allow mobile nodes to acquire new addresses while still using
previously allocated addresses.
6.9. Returning Home
A "home registration"), then the
home agent MUST multicast onto the home subnet (to the all-nodes
multicast address) a Neighbor Advertisement message [8] on behalf
of the mobile node detects that it has returned node, to its home network
through advertise the movement detection algorithm in use (Section 6.1),
when home agent's own link-layer
address for the mobile node detects that its node's home network prefix is again
on-link. IP address. 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, Target Address in
the mobile node Neighbor Advertisement message MUST be set the Care-of Address field to its own IPv6 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 node's
home address, and SHOULD retransmit the Binding Update until Advertisement MUST include a matching
Binding Acknowledgement message is received. Target Link-layer
Address option specifying the home agent's link-layer address. The mobile node MUST also send out
Solicited Flag (S) in the appropriate Neighbor Advertisement packets with the MUST NOT be set, since it was
not solicited by any Neighbor Solicitation message. The Override flag
Flag (O) in the Advertisement MUST be set, so indicating that its
neighbors the
Advertisement SHOULD override any existing Neighbor Cache entry at
any node receiving it.
Any node on its the home network subnet receiving this Neighbor Advertisement
message will thus update its Neighbor Cache to associate the relevant information mobile
node's home address with the home agent's link layer address, causing
it to transmit future packets for the mobile node in their Neighbor Caches. The instead to the
mobile node
MUST do this for both its link-local address and its node's home address.
The 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 packets can be repeated a small number
of message up to
MAX_ADVERT_REXMIT times to guard against occasional loss of packets increase its reliability. It is still
possible that some nodes on the home
network.
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7. Home Agent Considerations
7.1. Home Agent Care-of Address Registration
General processing subnet will not receive any of a received Binding Update that requests a
binding to
these Neighbor Advertisements, but these nodes will eventually be cached, is described in Section 5.2. However, if the
Home Registration (H) bit is set in the Binding Update, then the
receiving node MUST process the Binding Update as specified in this
section, rather than following the generall procedure specified in
Section 5.2.
To begin processing
able to detect the Binding Update, link-layer address change for the mobile node's
home agent MUST perform
the following sequence address, through use of tests:
- If the Neighbor Unreachability Detection [8].
In addition, while this node is not serving as a router that implements home agent
functionality, then the to this
mobile node MUST reject the Binding Update and
SHOULD return (it still has a Binding Acknowledgement message to the "home registration" entry for this mobile
node,
node in which the Code field is set its Binding Cache), it MUST act as a proxy for this mobile
node to 132 (Home registration
not supported).
- Else, reply to any received Neighbor Solicitation messages for it.
When a home agent receives a Neighbor Solicitation message, it MUST
check if the Home Target Address field specified in the Binding Update is not an
on-link IPv6 address with respect to message matches the home agent's current
Prefix List, then
address of any mobile node for which it has a Binding Cache entry
marked as a "home registration". If such an entry exists in its
Binding Cache, the home agent MUST reject reply to the Binding Update
and SHOULD return a Binding Acknowledgement Neighbor Solicitation
message to the mobile
node, in which the Code field is set to 133 (Not home network).
- Else, if the home agent chooses to reject the Binding Update for
any other reason (e.g., insufficient resources to serve another
mobile node as with a home agent), then Neighbor Advertisement message, giving the home agent SHOULD return a
Binding Acknowledgement message to the mobile node, in which the
Code field is set to an appropriate value to indicate
agent's own link-layer address as the reason link-layer address for the rejection.
If
specified Target Address. Likewise, if the mobile node included its
home agent does not reject link-local address and set the Home Link-Local Address (L) bit
in its Binding Update as described
above, then with which it becomes the registered with its home agent,
its home agent MUST also similarly act as a proxy for the mobile node. The
new
node's home agent (the receiving node) MUST then create link-local address while it has a new "home registration"
entry
(or update the existing entry) in its Binding Cache for this the mobile node's Home Address, node. Acting as described a proxy
in Section 5.2. In
addition, this way allows other nodes on the mobile node's home agent MUST mark this Binding Cache entry as a
"home registration" subnet to indicate that
resolve the node is serving as a mobile node's IPv6 home
agent for this binding. Binding Cache entries marked as a "home
registration" SHOULD be excluded from the normal cache replacement
policy used for the Binding Cache (Section 5.5) address and SHOULD NOT be
removed from the Binding Cache until the expiration of the Lifetime
period.
If IPv6 link-local
address, and allows the home agent was not already serving as a to to defend these addresses on
the home agent subnet for the
Home Duplicate Address specified in the Binding Update (the home agent did Detection [8].
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not already have
7.2. Primary Care-of Address De-registration
General processing of a received Binding Cache entry for this address marked as Update that requests a "home registration"),
binding to be deleted, is described in Section 6.3. However, if the
Home Registration (H) bit is set in the Binding Update, then the home agent
receiving node MUST multicast onto process the home network (to Binding Update as specified in this
section, rather than following the all-nodes multicast address), a Neighbor
Advertisement message on behalf of general procedure specified in
Section 6.3.
To begin processing the mobile node, with Binding Update, the fields
in home agent MUST perform
the Neighbor Advertisement set as follows:
Router Flag (R)
1 -- following sequence of tests:
- If the sending node (the home agent) is not a router.
Solicited Flag (S)
0 -- router that implements home agent
functionality, then the Neighbor Advertisement message is unsolicited.
Override Flag (O)
1 -- node MUST reject the advertisement Binding Update and
SHOULD override any existing Neighbor
Cache entry at the receiver, updating return a Binding Acknowledgement message to the receiver's cached
link-layer address for this Target Address.
Target Address
The mobile node's home address, copied from
node, in which the Home Address Status field of is set to 132 (Home registration
not supported).
- Else, if the Binding Update.
Options
The home agent MUST include at least a Target Link-layer
Address option in address for the Neighbor Advertisement message, binding in which the Link-Layer Binding Update
(the Source Address gives in the link-layer packet's IP header) is not an on-link
IPv6 address of with respect to the home
agent itself.
Any node on agent's current Prefix
List, then it MUST reject the home network receiving this Neighbor Advertisement Binding Update and SHOULD return a
Binding Acknowledgement message will thus update its Neighbor Cache to associate the mobile
node's node, in which the
Status field is set to 133 (Not home address with subnet).
If the home agent's link layer address, causing agent does not reject the Binding Update as described
above, then it to transmit future packets MUST delete any existing entry in its Binding Cache
for the this mobile node instead to node.
In addition, the home agent MUST multicast a Neighbor Advertisement
message (to the all-nodes multicast address), giving the mobile
node's home agent. Since multicasts on the local link (such address as Ethernet) are typically not guaranteed to be reliable, the Target Address, and specifying the mobile
node's link-layer address in a Target Link-layer Address option in
the Neighbor Advertisement message. The home agent MAY retransmit
this Neighbor Advertisement message a small
number of up to MAX_ADVERT_REXMIT times
to increase its reliability. It is still possible
that some reliability; any nodes on the home network will not receive any subnet that miss
all of these Neighbor Advertisements, but these nodes will Advertisements can also eventually be able
to detect the
link-layer address change for the mobile node's home address, through
use of Neighbor Unreachability Detection [9].
In addition, while this node is serving as a home agent [8].
7.3. Tunneling Intercepted Packets to a Mobile Node
For any packet sent to a mobile node (it has at least one entry marked as a "home registration" in
its Binding Cache), it SHOULD act 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 proxy for each such correspondent node of the mobile
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node to reply to any received Neighbor Solicitation messages for
it. When a Section 6.7
apply. The home agent receives uses a Neighbor Solicitation message, it
MUST check if Routing header to route the Target Address specified packet
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to the message matches
the Home Address of any mobile node for which it has a through the care-of address in the home agent's
Binding Cache
entry marked as a "home registration". If such an entry exists (the mobile node's primary care-of address, in its Binding Cache, this
case).
In addition, while the mobile node is away from home agent MUST reply to the Neighbor
Solicitation message with a Neighbor Advertisement message, giving and this node
is acting as the mobile node's home agent's own link-layer address as agent, the link-layer address for home agent intercepts
any packets on the specified Target Address.
7.2. Home Agent Care-of Address De-registration
General processing of a received Binding Update that requests a
binding home subnet addressed to be deleted, is the mobile node's
home address, as described in Section 5.3. However, if the
Home Registration (H) bit is set in the Binding Update, then 7.1. The home agent cannot
use a Routing header to forward these intercepted packets to the
receiving node MUST process
mobile node, since it cannot modify the Binding Update as specified packet in this
section, rather than following the generall procedure specified flight without
invalidating any existing IPv6 Authentication header present in
Section 5.3.
To begin processing the Binding Update,
packet [1].
For forwarding each intercepted packet to the mobile node, the
home agent MUST perform tunnel the following sequence of tests:
- If packet to the mobile node is not a router that implements home agent
functionality, then using IPv6
encapsulation [4]; the tunnel entry point node MUST reject is the Binding Update home agent,
and
SHOULD return a Binding Acknowledgement message to the mobile
node, in which the Code field tunnel exit point node is set to 132 (Home registration
not supported).
- Else, if the Home Address field in the Binding Update is not an
on-link IPv6 mobile node itself (using its
primary care-of address as registered with respect to the home agent's current
Prefix List, then it MUST reject the Binding Update and SHOULD
return agent). When a Binding Acknowledgement message
home agent encapsulates an intercepted packet for forwarding to the
mobile node, in
which the Code field is set to 133 (Not home network).
If the home agent does not reject sets the Binding Update as described
above, then it MUST delete any existing entry in its Binding Cache
for this mobile node's Home Address, as specified Source Address in the Binding
Update.
In addition, prepended
tunnel IP header to its own IP address, and sets the home agent SHOULD multicast a Neighbor Advertisement
message (to Destination
Address in the all-nodes multicast address), giving tunnel IP header to the mobile node's home address as primary care-of
address. When received by the Target Address, mobile node (using its primary care-of
address), normal processing of the tunnel header [4] will result in
decapsulation and specifying processing of the original packet by the mobile
node's link-layer address in a Target Link-layer Address option in
node.
7.4. Renumbering the Home Subnet
Neighbor Advertisement message. The home agent MAY retransmit
this Neighbor Advertisement message Discovery [8] specifies a small number of times to
increase its reliability, and any nodes on the home network that miss
all of these Neighbor Advertisements can also eventually detect the
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link-layer address change for the mobile node's home address, through
use of Neighbor Unreachability Detection [9].
7.3. Delivering Packets to a Mobile Node
Home agents cannot use Routing headers to deliver packets to the
mobile node, because they can't modify the packet and add to it
in flight. They must always use IPv6 encapsulation [5] for this
purpose.
When a home agent encapsulates a packet for delivery to the mobile
node, the home agent uses the care-of address as the destination
address in the outer IPv6 header. Since the mobile node is presumed
to be receiving packets at the care-of address, the delivery path
from the care-of address to the mobile node's home address is then
trivial.
Note that the home agent cannot insert a routing header, or
modify the destination address of the mobile node, because of IPv6
authentication mechanisms [1]. The home agent is expected to be
involved only rarely with the transmission of data to the mobile
node, because the mobile node will send Binding Updates as soon as
possible to its correspondent nodes.
7.4. Renumbering the Home Network
Neighbor Discovery [9] specifies a mechanism by which all mechanism by which all nodes on a
network
subnet can gracefully autoconfigure new addresses, say by each node
combining a new routing prefix with their its existing MAC link-layer address.
As currently specified, this mechanism works when the nodes are on
the same link as the router issuing the necessary multicast packets
to advertise the new routing prefix(es) appropriate for the link.
However, for mobile nodes away from home, special care must be taken
to allow the mobile nodes to renumber gracefully. The most direct
method of insuring ensuring this is for the home agent to encapsulated encapsulate and
tunnel the multicast packets to the primary care-of address of the each
mobile node for which it is serving as necessary. the home agent. The rules for
this are as follows:
- A mobile node assumes that its routing prefix has not changes changed
unless it receives authenticated router advertisement Router Advertisement messages
from its home agent that the prefix has changed.
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- When the mobile node is at home, the home agent does not tunnel
router advertisements
Router Advertisements to it.
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- The mobile node's home agent serves as a proxy for the mobile
node's home address and link-local address, including defending
these addresses for Duplicate Address Detection, while the mobile
node is registered with the home agent away from home.
- When a home network subnet prefix changes, the home agent tunnels router
advertisement Router
Advertisement packets to each mobile node which is currently
away from home and using a home address with the affected
routing prefix. Such tunneled router advertisements Router Advertisements MUST be
authenticated [1].
- When a mobile node receives a tunneled router advertisement Router Advertisement
containing a new routing prefix, it must perform the standard
autoconfiguration operation to create its new address
- When a mobile node returns to its home network, subnet, it must again
perform Duplicate Address Detection at the earliest possible
moment after it has registered with its home agent.
- A mobile node may send a router solicitation Router Solicitation to its home agent at
any time, within the constraints imposed by rate control in the
Neighbor Discovery specification [9]
Note that a mobile node is guaranteed that its home address is unique
and used by no other mobile node. However, in some circumstances it
may nevertheless be true that other nodes on its home network form
the same link-local address as the mobile node during the time when
the mobile node is away from its home network. Thus, there is the
requirement above that the mobile node perform Duplicate Address
Detection when it returns again to its home network. [8]
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8. Correspondent Node Considerations
8.1. Delivering Packets to a Mobile Node
The routing infrastructure of the Internet will normally route a
packet destined to a Operation
8.1. Movement Detection
A mobile node MAY use any combination of mechanisms available to
it to detect when its link-level point of attachment has moved
from one IP subnet to another. The primary movement detection
mechanism for Mobile IPv6 defined here uses the mobile node's home network,
if the Destination Address in the packet's facilities of
IPv6 header Neighbor Discovery, including Router Discovery and Neighbor
Unreachability Detection. The description here is based on the mobile
node's home address. Once the packet reaches
conceptual model of the home network, it
will be intercepted organization and data structures defined by the mobile node's home agent if the mobile
node is away from home, and will then be encapsulated using IPv6
encapsulation and tunneled to the mobile node's current primary
care-of address. Using this delivery mechanism, the sender need not
know that the node is mobile.
Correspondent
Neighbor Discovery [8].
Mobile nodes that have received SHOULD use Router Discovery to discover new routers and cached a Binding Update
for
on-link network prefixes; a mobile node, node MAY instead route packets directly to that send Router Solicitation
messages, or MAY wait for unsolicited (periodic) Router Advertisement
messages, as specified for Router Discovery [8]. Based on received
Router Advertisement messages, a mobile
node's care-of address. To do so, the correspondent node includes
a Routing header (in the same way as any
other node) maintains an entry in its Default Router List for each packet
router, and an entry in its Prefix List for each network prefix, that
it currently considers to be on-link. Each entry in these lists has
an associated invalidation timer value (extracted from the mobile node, Router
Advertisement) used to cause expire the
packet entry when it becomes invalid.
While away from home, a mobile node SHOULD select one router from its
Default Router List to be routed use as its default router, and one network
prefix advertised by that router from its Prefix List to the mobile node's care-of address use as
the last
intermediate routing point before reaching the final destination
of the mobile node's home address. When the packet arrives at the network prefix in its primary care-of address (which the address. A mobile node has
MAY also have associated with its additional care-of addresses, using other
network interface), normal processing of the Routing header by the prefixes from its Prefix List. The method by which a mobile
node will result in delivery of the packet to selects and forms a care-of address from the available network
prefixes is described in Section 8.2. The mobile node registers
its primary care-of address with its home agent, as the final destination of the packet.
For example, assuming no other use of the Routing header described in the
packet, the sender initializes the Destination Address
Section 8.3.
While away from home and using some router as its default router,
it is important for a 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 IPv6
header mobile node to detect
when it becomes unreachable to its default router, so that the mobile node's care-of address, and includes
node can take steps to ensure that any correspondent nodes attempting
to communicate with the it can still reach it through some other
route.
To detect when its default router becomes unreachable, a Type 0
Routing header [6] mobile
node SHOULD use Neighbor Unreachability Detection. As specified in the packet initialized as follows:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Hdr Ext Len | Routing Type=0|Segments Left=1|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Strict/Loose Bit Map |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Home Address +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Next Header
8-bit selector. Identifies the type of header immediately
following
Neighbor Discovery [8], while the Routing header.
Hdr Ext Len
8-bit unsigned integer. Length of the Routing header in
8-octet units, not including the first 8 octets. For this use
of the Type 0 Routing header, Hdr Ext Len mobile node is equal actively sending
packets to 2.
Routing Type
0
Segments Left
8-bit unsigned integer. Number of route segments remaining
before reaching (or through) its default router, the final destination. For this use of mobile node can
detect that the
Type 0 Routing header, Segments Left router is initialized to 1 by the
sender.
Reserved
8-bit reserved field. Initialized to zero for transmission;
ignored still reachable either through indications
from upper layer protocols on reception.
Strict/Loose Bit Map
24-bit bit-map, numbered 0 to 23, left-to-right. For this use
of the Type 0 Routing header, bit 0 of the Strict/Loose Bit Map mobile node that a connection is set
making "forward progress" (e.g., receipt of TCP acknowledgements for
new data transmitted), or through receipt of a Neighbor Advertisement
message form its default router in response to 1, indicating strict routing from the care-of
address an explicit Neighbor
Solicitation messages to it. Note that although this mechanism only
detects that the mobile node's home address (both addresses are
associated with default router has become unreachable
to the mobile node itself).
Home Address
The home address of while the destination mobile node.
If a correspondent node receives an ICMP Host Unreachable or Network
Unreachable message after is actively sending a packet 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 using
its cached care-of address, to detect when it SHOULD delete the cache entry from has become unreachable to its Binding Cache until information about
default router, however, the mobile node's current
care-of address becomes available (via a Binding Update).
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9. Authentication and Replay Protection
When sending Binding Updates, many cases for a mobile node uses the Identification
field in the option, in conjunction to
continually probe its default router with the IPv6 Authentication
Header, Neighbor Solicitation
messages even when it is not otherwise actively sending packets to protect against replays of the Binding Update. The style
it. Instead, a mobile node SHOULD consider receipt of replay protection specified for the any IPv6 Binding Update involves
the use of a timestamp
packets from its current default router as an indication that it is
still reachable from the Identification data. Accordingly router. Both packets from the
mobile node router's IP
address and the target of (IPv6) packets from its Binding Update have to roughly
agree on link-layer address (e.g., those
forwarded but not originated by the current time. Stale Binding Updates MUST router) SHOULD be rejected.
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10. Routing Multicast Packets
A considered.
Since the router SHOULD be sending periodic multicast Router
Advertisement messages, the mobile node that is connected will have frequent
opportunity to its home network functions just
like any other (stationary) node. Thus, when check if it is at home, a mobile
node functions identically still reachable to its default router,
even in the absence of other multicast senders and receivers.
This section therefore describes packets to it from the behavior router. On some
types of a network interfaces, the mobile node MAY also supplement this
by setting its network interface into "promiscuous" receive mode,
so that it is not able to receive all packets on its home network.
In order receive multicasts, a the link, including
those not link-level addressed to it. The mobile node must join will then
be able to detect any packets sent by the multicast
group. Mobile nodes MAY join multicast groups router, in order to receive
transmissions in one of two ways. First, they MAY join to
detect reachability from the group
via a (local) multicast router router. This may be useful on very low
bandwidth (e.g., wireless) links, but its use MUST be configurable on
the visited subnet. This option
assumes mobile node.
If the above means do not provide indication that there the mobile node
is a multicast still reachable from its current default router present on (i.e., the
mobile node receives no packets form the router for a period of
time), then the visited
subnet. The mobile node SHOULD use its dynamically acquired care-of
address (if actively probe the router with
Neighbor Solicitation messages, even if it has acquired one) as is not otherwise actively
sending packets to the source IPv6 address of its
multicast group membership control message packets. Otherwise, router. If it
MAY use its home address.
Alternatively, receives a solicited Neighbor
Advertisement message in response from the router, then the mobile
node which wishes to receive multicasts can
join groups via a bi-directional tunnel to its home agent, assuming deduce that its home agent it is a multicast router. The still reachable. It is expected that the
mobile node tunnels
the appropriate multicast group membership control packets will in most cases be able to determine its
home agent reachability
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from the home agent forwards multicast router by listening for packets down the
tunnel to from the mobile node. The home agent must tunnel the packet
directly to 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's dynamically acquired care-of address,
or, the packet must be tunneled first to
node. However, a mobile node MUST NOT assume that all link-layer
mobility indications from lower layers indicate a movement of the
mobile node's home
address and then recursively tunneled link-layer connection to a new IP subnet, such that the
mobile node's care-of
address.
A mobile node which wishes would need to send packets switch to a multicast group also
has two options: (1) send directly on the visited network; or (2)
send via a tunnel to its home agent. Because multicast routing in
general depends upon new default router and primary
care-of address. Upon lower-layer indication of link-layer mobility,
the IPv6 source address, a mobile node which
sends multicast packets directly on the visited SHOULD send Router Solicitation messages to determine
if new routers (and new on-link network MUST use a
dynamically acquired care-of address as the IPv6 source address.
Similarly, prefixes) are present on its
new link.
Such lower-layer information might also be useful to a mobile node which tunnels a multicast packet in
deciding to switch its home
agent MUST use its home address as the IPv6 source primary care-of address to one of both the (inner) multicast packet and other
care-of addresses it has formed from the (outer) encapsulating packet.
This second option assumes that on-link network prefixes
currently available through different default routers from which the home agent
mobile node is reachable. For example, a multicast mobile node MAY use signal
strength or signal quality information (with suitable hysteresis)
for its link with the available default routers to decide when to
switch to a new primary care-of address using that default 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.
8.2. Forming New Care-of Addresses
After detecting that its link-layer point of attachment has moved
from one IPv6 subnet 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 network 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 network prefix, a
mobile node MAY form a new (non-primary) care-of address using that
network 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 (registered with its home agent), but it MAY have an
additional care-of address for each network prefix on its current
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11. Constants
INITIAL_BINDACK_TIMEOUT 1 second
MAX_BINDACK_TIMEOUT 256 seconds
MAX_UPDATE_RATE 1 per second
SLOW_UPDATE_RATE once per 10 seconds
Acknowledgements
We would like to thank Thomas Narten for contributing valuable
discussion and reviewing this draft, and for helping
link. Furthermore, since a wireless network interface may actually
allow a mobile node to shape some be reachable on more than one link at a time
(i.e., within wireless transmitter range of
the recent changes relevant 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 8.9.
As described in Section 3, in order to form a new care-of address,
a mobile node MAY use either stateless [14] or stateful (e.g.,
DHCPv6 [3]) address autoconfiguration. If a mobile node needs to
send packets as part of the operation method of Neighbor Discovery.
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it MUST use an IPv6 13 June 1996
References
[1] R. Atkinson. IP Authentication Header. RFC 1826, August 1995.
[2] R. Atkinson. Security Architecture for link-local address rather than its own IPv6
home address as the Internet Protocol.
RFC 1825, August 1995.
[3] J. Bound and C. Perkins. Dynamic Host Configuration Protocol
for IPv6. draft-ietf-dhc-dhcpv6-05.txt -- work Source Address in progress,
June 1996.
[4] A. Conta and S. Deering. Internet Control Message Protocol
(ICMPv6) for the Internet Protocol Version 6 (IPv6). RFC 1885,
December 1995.
[5] A. Conta and S. Deering. Generic Packet Tunneling in IPv6.
draft-ietf-ipngwg-ipv6-tunnel-01.txt - work in progress,
February 1996.
[6] S. Deering and R. Hinden. Internet Protocol, Version 6 (IPv6)
Specification. RFC 1883, December 1995.
[7] D. Haskin and E. Allen. IP Version 6 over PPP.
draft-ietf-ipngwg-pppext-ipv6cp-03.txt - work in progress, June
1996.
[8] David B. Johnson 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 subnet. For example, a mobile node may be
statically configured with an IPv6 address assigned by the system
administrator of some foreign subnet, for its use while visiting that
subnet. If so, rather than using address autoconfiguration to form
a new care-of address using this network prefix, the mobile node
SHOULD use its own pre-assigned address as its care-of address on
this subnet.
8.3. Sending Binding Updates to the Home Agent
After deciding to change its primary care-of address as described
in Sections 8.1 and 8.2, 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 Home Registration (H)
bit is set in the Binding Update. The mobile node also sets the
Acknowledge (A) bit in the Binding Update, requesting the home
agent to return a Binding Acknowledgement message in response to
this Binding Update. As described in Section 4.2, the mobile node
SHOULD retransmit this Binding Update to its home agent until it
receives a matching Binding Acknowledgement message. 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).
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8.4. Sending Binding Updates to Correspondent Nodes
A mobile node MAY send a Binding Update to any correspondent node at
any time (subject to the rate limiting defined in Section 8.7). In
any Binding Update sent by a mobile node, the Care-of Address field
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
a 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. If, instead, the Care-of Address field
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 field 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,
- The remaining lifetime of the binding, initialized from the
Lifetime field of 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 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
existing Binding Update List 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 8.3), the mobile node will also typically send a Binding
Update to each correspondent node for which an entry exists in the
mobile node's Binding Update List. Thus, correspondent nodes are
generally kept updated and can send almost all packets directly to
the mobile node using the mobile node's current binding.
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
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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 in its Binding Cache entry for the mobile node, the
mobile node SHOULD return a Binding Update to the sender giving its
current care-of address. 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) IP header is equal
to any of the mobile node's care-of addresses.
- The Destination Address in the original (inner) IP header is
equal to 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 this comparison rather than the
Destination Address in the original IP header.
- The Source Address in the tunnel (outer) IP header differs from
the Source Address in the original (inner) IP header.
The destination address to which the Binding Update should be sent in
response to receiving a packet meeting all of the tests above, is the
Source Address in the original (inner) IP header of the packet.
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 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.
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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 4.1. No other IPv6 nodes are authorized to send Binding
Updates on behalf of a mobile node.
8.5. 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 SHOULD send a Binding
Update message to its previous default router, giving its new care-of
address. If the mobile node sends such a Binding Update, the Source
Address 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 field 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.
Note that the previous router does not necessarily know the mobile
node's home address as part of this sequence of events.
If any subsequent packets arrive at this previous router for
forwarding to the mobile node's old primary care-of address,
the router SHOULD encapsulate each such packet (using IPv6
encapsulation [4]) and tunnel it to the mobile node at its new
primary care-of address. Moreover, for the lifetime of the "home
registration" Binding Cache entry at this router, this router MUST
act as a proxy for the mobile node's previous care-of address,
for purposes of participation in Neighbor Discovery [8], in the
same way as any home agent does for a mobile node's home address
(Section 7.1). This allows the router to intercept packets addressed
to the mobile node's previous care-of address, and to encapsulate and
tunnel them to the mobile node's new care-of address, as described in
Section 7.3.
8.6. Retransmitting Binding Updates
If, after sending a Binding Update in which the Acknowledge (A)
bit is set, a mobile node fails to receive an acceptable 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 he same Identification value as the original
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transmission. The retransmissions by the mobile node MUST use
an exponential back-off process, in which 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.
8.7. 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 correspondent node. After sending 5
consecutive Binding Updates to a particular correspondent node with
the same care-of address, the mobile node SHOULD reduce its rate
of sending Binding Updates to that correspondent node, 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 that
the correspondent node will eventually be able to process a Binding
Update and begin to route its packets directly to the mobile node at
its new care-of address.
8.8. Receiving Binding Acknowledgements
Upon receiving a packet carrying a Binding Acknowledgement, a mobile
node MUST validate the packet according to the following tests:
- The packet contains an IP Authentication header and the
authentication is valid [1]. The Authentication header is
assumed to provide both authentication and integrity protection.
- The Option Length field in the option is greater than or equal to
8 octets.
- The Identification field is valid.
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.
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 MUST update the corresponding entry in its Binding Update
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List to indicate that the Binding Update has been acknowledged.
The mobile node MUST thus stop retransmitting the Binding Update.
- If the Status field indicates that the Binding Update was not
accepted (the Status field is greater than or equal to 128), then
the mobile node MUST delete the corresponding Binding Update List
entry. Optionally, the mobile node MAY take steps to correct the
cause of the error and retransmit the Binding Update, subject to
the rate limiting restriction specified in Section 8.7.
8.9. Using Multiple Care-of Addresses
As described in Section 8.2, a mobile node MAY have more than
one care-of address at a time. Particularly in the case of many
wireless networks, a mobile node effectively may be reachable
through multiple link-level points of attachment at the same time
(e.g., with overlapping wireless cells), on which different on-link
network 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 network prefixes, based on the movement detection
mechanism in use (Section 8.1). When the mobile node selects a new
primary care-of address, it MUST register it with its home agent
through a Binding Update message with the Home Registration (H) and
Acknowledge (A) bits set, as described in Section 8.3.
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 [3], the
mobile node may not wish to release the address immediately upon
switching to a new primary care-of address. The stateful address
autoconfiguration server will allow mobile nodes to acquire new
addresses while still using previously allocated addresses.
8.10. Returning Home
A mobile node detects that it has returned to its home subnet through
the movement detection algorithm in use (Section 8.1), when the
mobile node detects that the network prefix of its home subnet 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
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MUST set the Care-of Address field to its own IPv6 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 message is received.
In addition, the mobile node MUST multicast onto the home subnet
(to the all-nodes multicast address) a Neighbor Advertisement
message [8], to advertise its link-layer address for its own IPv6
home address. The Target Address in this Neighbor 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. Similarly, the
mobile node MUST multicast a Neighbor Advertisement message to
advertise its link-layer address for its IPv6 link-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 subnet will not receive any of these Neighbor
Advertisements, but these nodes will eventually be able to recover
through use of Neighbor Unreachability Detection [8].
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9. Routing Multicast Packets
A mobile node that is connected to its home subnet 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
receivers. This section therefore describes the behavior of a mobile
node that is not on its home subnet.
In order receive packets sent to some multicast group, a mobile node
must join the that multicast group. One method by which a mobile
node MAY join the group is via a (local) multicast router on the
foreign subnet being visited. This option assumes that there is a
multicast router present on the foreign subnet. The mobile node
SHOULD use its care-of address sharing a network prefix with the
multicast router, as the source IPv6 address of its multicast group
membership control message packets.
Alternatively, a mobile node MAY join multicast groups via a
bi-directional tunnel to its home agent, assuming that its home agent
is a multicast router. The mobile node tunnels the appropriate
multicast group membership control packets to its home agent, and the
home agent forwards multicast packets down the tunnel to the mobile
node. The home agent MUST tunnel the packet directly to the mobile
node's primary care-of address.
A mobile node that wishes to send packets to a multicast group
also has two options: (1) send directly on the foreign subnet
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 IP header of the multicast packet, a mobile node that sends
multicast packets directly on the foreign subnet MUST use its
care-of address as the IPv6 Source Address of each multicast packet.
Similarly, a mobile node that tunnels a multicast packet to its home
agent MUST use its home address as the IPv6 Source Address of both
the (inner) multicast packet and the (outer) encapsulating packet.
This second option assumes that the home agent is a multicast router.
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10. 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_ADVERT_REXMIT 3
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11. Security Considerations
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 [2].
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 Charles E. Perkins. Route Optimization other active attacks.
Users who have sensitive data that they do not wish others to see
should use mechanisms outside the scope of this document (such as
encryption) to provide appropriate protection. Users concerned about
traffic analysis should consider appropriate use of link encryption.
If absolute 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 pinpoint the location of the mobile node. Such
mechanisms are all beyond the scope of this document.
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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 draft. We would
particularly like to thank Thomas Narten and Erik Nordmark 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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progress, February 1996.
[9] T. Narten, E. Nordmark, IPv6 26 November 1996
A. Open Issues
A.1. Session Keys with Local Routers
In the IPv4 route optimization proposal [7], a mechanism is outlined
whereby a session key can be established between foreign agents
and mobile nodes, without requiring any pre-established security
relationship between them. A similar mechanism could be defined for
IPv6, to avoid the need for a possibly time-consuming negotiation
between routers and W. Simpson. mobile nodes for the purpose of obtaining the
session key, which under many circumstances would only be used once.
This mechanism, if needed, can be specified completely outside
the Mobile IPv6 Neighbor
Discovery. draft-ietf-ipngwg-discovery-03.txt -- work in
progress, November 1995.
[10] Joyce K. Reynolds protocol and Jon Postel. Assigned Numbers. RFC 1700,
October 1994.
[11] Fumio Teraoka. draft-teraoka-ipv6-mobility-sup-02.txt.
Internet Draft -- would amount to a way of creating a
dynamic security association between two nodes which do not share an
existing trust relationship, but which need to agree on a key for
some particular purpose (here, allowing the future authentication of
a Binding Update). Hopefully, the work in progress, January 1996.
[12] S. Thomson and T. Narten. IPv6 Stateless of the IP Security Working
Group will allow this function to be performed appropriately for
mobile nodes, say by a Diffie-Hellman key exchange.
A.2. Source Address
Autoconfiguration. draft-ietf-addrconf-ipv6-auto-06.txt
- work Filtering by Firewalls
The current specification does nothing to permit mobile nodes to
send their packets through firewalls which filter out packets with
the "wrong" source IPv6 addresses in progress, November 1995.
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mobile node's home address may be unlikely to fall within the ranges
required to satisfy the firewall's criteria for further delivery.
As indicated by recent discussion, firewalls are unlikely to
disappear. Any standardized solution [13] to the firewall problem
based on hiding the non-local source address outside the source
address field of the IP header is likely to fail. Any vendor or
facilities administrator wanting to filter based on the address in
the IPv6 13 June 1996
A. Open Issues
A.1. Session Keys with Local Routers
In source address field would also quickly begin filtering on
hidden source addresses.
Assume, for the IPv4 route optimization proposal [8], moment, that a mechanism mobile node is outlined
whereby able to establish a session key can be established between foreign agents
and
secure tunnel through a firewall protecting the domain in which
a correspondent node is located. The mobile nodes, without requiring any pre-established security
relationship between them. A similar mechanism node could be defined for
IPv6, then
encapsulate its packet so that the outer IP header was addressed
to avoid the need for a possibly time-consuming negotiation
between routers firewall and used the mobile nodes for node's care-of address as the purpose of obtaining
source address. When the
session key, which under many circumstances firewall decapsulates, it would only be used once.
This mechanism, if needed, can be specified completely outside
the Mobile IPv6 protocol and would amount to a way of creating a
dynamic security association between two nodes which do not share an
existing trust relationship, but which need able to agree
authenticate the inner packet based (correctly) on a key for
some particular purpose (here, allowing the future mobile node's
home address. After the authentication is performed, the firewall
could forward the packet to the correspondent node as desired. This
simple procedure has the feature that it requires the minimal amount
of
a Binding Update). Hopefully, encapsulation, no assistance by routers or other agents, and that
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the work of firewall can establish a security relationship with the IP Security Working
Group will allow this function to be performed appropriately for mobile nodes, say by a Diffie-Hellman key exchange.
A.2. Source
node based on its home (i.e., permanent) address.
A.3. Dynamic Home Agent Address Filtering by Firewalls
The current specification does nothing to permit Discovery
It is useful for a mobile nodes node to be able to send their packets through firewalls which filter out packets with a Binding Update
its home agent without explicitly knowing the "wrong" source IPv6 addresses in home agent's address.
For example, since the IPv6 packet header. The mobile node's home address node was last at home, it may be unlikely have
become necessary to fall within replace the ranges
required node serving as its home agent due
to satisfy the firewall's criteria for further delivery.
As indicated by recent discussion, firewalls are unlikely to
disappear. Any standardized solution [11] failure of the original node or due to reconfiguration of the firewall problem
based on hiding
home subnet. It thus may not always be possible or convenient for a
mobile node to know the non-local source exact address outside of its own home agent. Several
methods of allowing a mobile node to dynamically discover the source address field
of a router in its home subnet are currently under consideration.
A.4. Replay Protection for Binding Updates
Some transforms for use in conjunction with the IP Authentication
Header [1] provide support for replay protection [9, 6]. Ideally,
such transforms would directly support the needs of Mobile IPv6 header is likely to fail. Any vendor or
facilities administrator wanting
for providing replay protection for Binding Updates and Binding
Acknowledgements. However, this does not currently appear to filter based on the address in be
the IPv6 source address field would also quickly begin filtering on
hidden source addresses.
Assume, case. These transforms provide optional support for accepting
packets out of order, through use of an "out of order window" in the moment, that a mobile node is able
receiver, and it does not currently seem to establish a
secure tunnel through a firewall protecting be specified how the domain in which
size (or presence) of such a correspondent node window can be controlled. For Binding
Updates, it is located. The mobile node could then
encapsulate its packet so important that any packets containing a Binding
Update that arrive at the outer IPv6 header was addressed
to the firewall and used receiver do so strictly in the mobile node's care-of address order sent
(although some may harmlessly be dropped, as long as a later Binding
Update does arrive). Without control of the
source address. When window at the firewall decapsulates, it would receiver,
this ordering requirement on Binding Update delivery cannot be able
supported directly by these transforms, although these transforms do
use a sequence number to
authenticate the inner packet based (correctly) on the mobile node's
home address. After support their own replay protection.
The Identification field in the authentication Binding Update (and Binding
Acknowledgement) is performed, currently specified in this document for use
in sequencing Binding Updates at the firewall
could forward receiver, and in matching
returned Binding Acknowledgements with outstanding Binding Updates
at the packet to sender. The use of this field in this manner, together with
the correspondent node as desired. This
simple procedure has use of the feature current IP Authentication transforms that it requires supports
replay protection, seems to support the minimal amount
of encapsulation, no assistance by routers or other agents, and necessary replay protection
requirements for Mobile IPv6, although it seems that the need for two
sequence numbers in the packet (one for IP Authentication and one for
Mobile IPv6) could be simplified.
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References
[1] Randall Atkinson. IP Authentication header. RFC 1826, August
1995.
[2] S. M. Bellovin. Security problems in the firewall can establish a security relationship TCP/IP protocol suite.
ACM Computer Communications Review, 19(2), March 1989.
[3] Jim Bound and Charles Perkins. Dynamic Host Configuration
Protocol for IPv6 (DHCPv6). Internet-Draft,
draft-ietf-dhc-dhcpv6-07.txt, August 1996. Work in progress.
[4] Alex Conta and Stephen Deering. Generic packet
tunneling in IPv6 specification. Internet-Draft,
draft-ietf-ipngwg-ipv6-tunnel-02.txt, June 1996. Work
in progress.
[5] Stephen E. Deering and Robert M. Hinden. Internet Protocol
version 6 (IPv6) specification. RFC 1883, December 1995.
[6] Shu jen Chang and Robert Glenn. HMAC-SHA IP authentication with the mobile
node based on its home (i.e., permanent) address.
replay prevention. Internet-Draft,
draft-ietf-ipsec-ah-hmac-sha-04.txt, November 1996. Work in
progress.
[7] David B. Johnson and Charles Perkins. Route optimization in
Mobile IP. Internet-Draft, draft-ietf-mobileip-optim-04.txt,
February 1996. Work in progress.
[8] Thomas Narten, Erik Nordmark, and William Allen Simpson.
Neighbor Discovery for IP version 6 (IPv6). RFC 1970, August
1996.
[9] Michael J. Oehler and Robert Glenn. HMAC-MD5 IP
authentication with replay prevention. Internet-Draft,
draft-ietf-ipsec-ah-hmac-md5-04.txt, November 1996. Work in
progress.
[10] J. B. Postel. User Datagram Protocol. RFC 768, August 1980.
[11] J. B. Postel, editor. Transmission Control Protocol. RFC 793,
September 1981.
[12] Joyce K. Reynolds and Jon Postel. Assigned numbers. RFC 1700,
October 1994.
Johnson and Perkins Expires 13 December 26 May 1997 [Page 47]
INTERNET-DRAFT Mobility Support in IPv6 26 November 1996
[13] Fumio Teraoka. Mobility support in IPv6. Internet-Draft,
draft-teraoka-ipv6-mobility-sup-03.txt, April 1996. Work in
progress.
[14] Susan Thomson and Thomas Narten. IPv6 stateless address
autoconfiguration. RFC 1971, August 1996.
Johnson and Perkins Expires 26 May 1997 [Page 41] 48]
INTERNET-DRAFT Mobility Support in IPv6 13 June 26 November 1996
Chair's Address
The Working Group can be contacted via its current chair: chairs:
Jim Solomon
Motorola, Inc.
1301 E. Algonquin Rd.
Schaumburg, IL 60196
Work: +1-847-576-2753
USA
Phone: +1 847 576-2753
E-mail: solomon@comm.mot.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
Johnson and Perkins Expires 26 May 1997 [Page 49]
INTERNET-DRAFT Mobility Support in IPv6 26 November 1996
Authors' Addresses
Questions about this document can also be directed to the authors:
David B. Johnson
Computer Science Department
Carnegie Mellon University
Computer Science Department
5000 Forbes Avenue
Pittsburgh, PA 15213-3891
Work:
USA
Phone: +1 412 268-7399
Fax: +1 412 268-5576
E-mail: dbj@cs.cmu.edu
Charles Perkins
Room H3-D34
IBM Corporation
T. J. Watson Research Center
IBM Corporation
Room H3-D34
30 Saw Mill River Rd.
Hawthorne, NY 10532
Work:
USA
Phone: +1 914 789-7350
Fax: +1 914 784-6205
E-mail: perk@watson.ibm.com
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