WDIFF

draft-ietf-addrconf-ipv6-auto-03.txt --> draft-ietf-addrconf-ipv6-auto-04.txt

ADDRCONF Working Group Susan Thomson (Bellcore) Thomson, Bellcore
INTERNET-DRAFT July 7, Thomas Narten, IBM
<draft-ietf-addrconf-ipv6-auto-04.txt> October 4, 1995
<draft-ietf-addrconf-ipv6-auto-03.txt>

IPv6 Stateless Address Autoconfiguration

Status of this Memo

This document is a submission to the ADDRCONF Working Group of the
Internet Engineering Task Force (IETF). Comments should be submitted
to the addrconf@cisco.com mailing list.

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. Internet Drafts may be updated, replaced, or obsoleted by
other documents at any time. It is not appropriate to use Internet
Drafts as reference material or to cite them other than as a "working
draft" or "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 ds.internic.net, nic.nordu.net, ftp.nisc.sri.com or
munnari.oz.au.

Distribution of this memo is unlimited.

This Internet Draft expires April 4, 1996.

Abstract

This document specifies how a node configures a link-local address
per interface, and how hosts autoconfigure addresses for their
interfaces in IP version 6. In particular, the document describes the
steps a host configures a list of global or site-
local addresses per interface, without any manual configuration.
Stateless takes in determining whether address autoconfiguration is only one mechanism available
should be used, and if so, whether to hosts; stateful address configuration is also available. While use the stateful address configuration is outside mechanism, the scope of this document,
it is specified how hosts determine which configuration method must
be used. The
stateless mechanism or both. This document also specifies a protocol for detecting
whether stateless
address autoconfiguration, and how nodes verify the uniqueness of an
address is a duplicate when before assigning it to an interface. Stateful address
autoconfiguration is initially configured.

Expires January 7, 1995 specified elsewhere.

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Contents

Status of this Memo....................................... 1

1. INTRODUCTION.......................................... 3

2. TERMINOLOGY........................................... 4
2.1. Requirements..................................... 7

3. DESIGN GOALS.......................................... 8

4. PROTOCOL OVERVIEW..................................... 9
4.1. Site Renumbering................................. 10

5. PROTOCOL SPECIFICATION................................ 11
5.1. Host Configuration Variables..................... 11
5.2. Autoconfiguration-Related Variables.............. 12
5.3. Creation of Link-Local Addresses................. 12
5.4. Verifying The Uniqueness Of An Address........... 13
5.4.1. Message Validation.......................... 14
5.4.2. Sending Neighbor Solicitation Messages...... 14
5.4.3. Receiving Neighbor Solicitation and Advertisement Messages 15
5.5. Creation of Global- and Site-Local Addresses..... 16
5.5.1. Sending Router Solicitations................ 16
5.5.2. Absence of Router Advertisements............ 16
5.5.3. Router Advertisement Processing............. 16
5.5.4. Address Lifetime Expiry..................... 18
5.6. Configuration July Consistency........................ 18

6. OPEN ISSUES/TODO...................................... 19

7. SECURITY CONSIDERATIONS............................... 20

8. REFERENCES............................................ 20

AUTHORS' ADDRESSES........................................ 20

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1. INTRODUCTION

In IPv6, a host has two mechanisms available to form a global

This document specifies how hosts autoconfigure their interfaces in IP
version 6. The autoconfiguration process includes determining what
information should be autoconfigured (addresses, other information, or
site-local address that require no manual configuration: the state-
less method
both), and in the stateful method. In case of addresses, whether they should be obtained
through the stateless method, no
external state is maintained for mechanism, the purpose of indicating to stateless mechanism, or both. This
document also specifies stateless address autoconfiguration. Stateful
address autoconfiguration is specified elsewhere.

IPv6 defines both a host
the list of addresses to use for an interface. Rather, stateful and stateless address autoconfiguration
mechanism. Stateless autoconfiguration requires no manual configuration
of hosts, minimal (if any) configuration of routers, and no additional
servers. The stateless mechanism allows a host forms to generate its own
addresses using a
list combination of addresses algorithmically locally available information and
information advertised by concatenating each of the net-
work routers. Routers advertise prefixes of that
identify the attached link to subnet(s) associated with a link, while hosts generate an
"interface token" that uniquely identifies an interface token unique per
link. The interface token on a subnet. An
address is defined to be link-dependent and may be formed by combining the hardware address, two. In the absence of routers, a
host can only generate link-local addresses. However, link-local
addresses are sufficient for example. allowing communication among nodes attached
to the same link.

In contrast, state is maintained
in the stateful address configuration, typically in autoconfiguration model, hosts obtain interface
addresses from a server. For
example, the IPv6 Dynamic Host Configuration Protocol is an example Servers maintain a database that keeps track
of stateful address autoconfiguration.

Stateless autoconfiguration is designed to make address configuration
very simple which addresses have been assigned to use and implement, and is suitable for environments
with simple topologies, e.g. routerless networks, and for environ-
ments where system administrative control is not desired, e.g. plug-
and-play environments. which hosts. In contrast, addition to
addresses, stateful address servers can also supply configuration
is designed to support flexible address assignment and is suitable
for more sophisticated topologies information
and for environments where system
administrative control is desired, e.g. corporate networks.

Any node can use stateless address parameters to a host. The stateful autoconfiguration mechanism
allows hosts to form obtain addresses, other configuration information or
both from a server. Stateless and stateful autoconfiguration complement
each other. For example, a link-
local address per interface. A host can use either stateless or
stateful autoconfiguration (or both) to
configure global or site-
local addresses for an interface. its own addresses, but use stateful autoconfiguration to
obtain other information. Stateful autoconfiguration is described in
[DHCPv6].

The choice of mechanism for confi-
guring global or site-local addresses stateless approach is itself configurable, and
requires no manual configuration per host.

One of the basic assumptions of stateless autoconfiguration used when a site is that not particularly concerned
with the token used to form exact addresses per interface is at least hosts use, so long as they are unique per
link. However, whatever the and
properly routable. The stateful approach is used when a site requires
tighter control over exact address assignments. Both stateful and
stateless address autoconfiguration may be used simultaneously. The
site administrator specifies which type of tokens used, interface tokens are
not guaranteed autoconfiguration to always be unique in practice because use
through the setting of errors appropriate fields in
assignment. Thus, it is possible that IPv6 addresses formed using
stateless autoconfiguration are not unique among all nodes on a link.
Since duplicate Router Advertisement
messages [DISCOVERY].

IPv6 addresses are very difficult leased to track down when
they occur, this document also specifies a procedure an interface for detecting
duplicate addresses. Note a fixed (possibly
infinite) length of time. Each address has an associated lifetime that
indicates how long the algorithm does not only apply to
addresses autoconfigured using the stateless mode. It should be used address is bound to verify an interface. When a lifetime
expires, the uniqueness of any address, for example, addresses con-
figured using binding (and address) becomes invalid and the stateful mode or manually configured addresses.

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This document describes how a node configures a link-local address
per

be reassigned to another interface using stateless elsewhere in the Internet. To handle
the expiration of address autoconfiguration, and how a
host configures global or site-local unicast addresses per interface
using stateless bindings gracefully, an address autoconfiguration. Stateful goes through
two distinct phases while assigned to an interface. Initially, an
address autocon-
figuration is outside "preferred", meaning that its use in arbitrary communication
is unrestricted. Later, an address becomes "deprecated" in anticipation
that its current interface binding will become invalid. While in a
deprecated state, the scope use of this document. However, address is discouraged, but not strictly
forbidden. New communication (e.g., the docu-
ment does specify how opening of a host determines whether to new TCP
connection) gives preference to using a non-deprecated address, with use
of the stateless
mechanism or deprecated address restricted to applications that have been
using the stateful mechanism for configuring global or site-
local addresses.

The deprecated address already and would have difficulty switching
to another address without a service disruption.

Finally, this document also describes the algorithm used by a node employs to detect if verify
that an address it is about to assign to an interface is unique on the
link. The "duplicate address detection" algorithm is used before an
address is actually used, independent of whether the address was
obtained via stateless or stateful autoconfiguration.

The autoconfiguration process specified in this document applies only to
hosts and not routers. Since host autoconfiguration uses information
advertised by routers, routers will need to be configured by some other
means. However, it is possible for routers to use the mechanism
described in this document for generating a link-local address. All
nodes (not only hosts) should use the duplicate when initially configured.

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procedure.

Section 2 provides definitions for terminology used throughout this
document. Section 3 describes the design goals that lead to the current
autoconfiguration procedure. Section 4 provides an overview of the
protocol, while Section 5 describes the protocol in detail.

2. TERMINOLOGY

IP - Internet Protocol Version 6. The terms IPv4 and IPv6
are used only in contexts where necessary to avoid
ambiguity.

node - a device that implements IPv6. IP.

router - a node that forwards IPv6 IP packets not explicitly
addressed to itself.

host - any node that is not a router.

upper layer - a protocol layer immediately above IPv6. IP. Examples are

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transport protocols such as TCP and UDP, control
protocols such as ICMP, routing protocols such as OSPF,
and internet or lower-layer protocols being "tunneled"
over (i.e., encapsulated in) IPv6 IP such as IPX, AppleTalk,
or IPv6 IP itself.

link - a communication facility or medium over which nodes can
communicate at the link layer, i.e., the layer
immediately below IPv6. IP. Examples are Ethernets (simple
or bridged); PPP links; X.25, Frame Relay, or ATM
networks; and internet (or higher) layer "tunnels",
such as tunnels over IPv4 or IPv6 itself.

neighbors - nodes attached to the same link.

interface - a node's attachment to a link.

autoconfigurable interface
- an interface that has been configured by system
management to perform autoconfiguration.

packet - an IPv6 IP header plus payload.

link MTU - the maximum transmission unit, i.e., maximum packet
size in octets, that can be conveyed in one piece over
a link.

target - a node about which address resolution information is
sought, or a node which is the new first-hop when being
redirected.

address - an IPv6-layer IP-layer identifier for an interface or a set of
interfaces.

unicast address
- an identifier for a single interface. A packet sent to
a unicast address is delivered to the interface

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identified by that address.

anycast

multicast address
- an identifier for a set of interfaces (typically
belonging to different nodes). A packet sent to an
anycast a
multicast address is delivered to one of the all interfaces
identified by that address (the "nearest" one,
according to the routing protocols' measure of
distance). address.

solicited-node multicast address
- an identifier for a set of interfaces (typically
belonging to different nodes). A packet sent to a multicast address is delivered to all interfaces
identified by that address. which Neighbor Solicitation
messages are sent. The algorithm for computing the
address is given in [DISCOVERY].

link-layer address
- a link-layer identifier for an interface. Examples are
include IEEE 802 addresses for Ethernet links, links and E.164
addresses for ISDN links.

link-local address
- an address with a having link-only scope that is limited can be used to
the locally
reach neighboring nodes attached to the same link. All

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interfaces have a link-local unicast address.

site-local address
- an address with a having scope that is limited to the local
site.

global address
- an address with unlimited scope.

communication
- any packet exchange between nodes that requires
or recommends that
the address of each node used in the exchange remain
the same for the duration of the packet exchange.
Examples are a TCP connection or a UDP request-response.

deprecation lifetime request-
response.

tentative address
- indicates the time at which an address should no
longer be used as whose uniqueness on a source link is being
verified, prior to its assignment to an interface. A
tentative address in new
communications. The deprecation lifetime must be
less than or equal is not considered assigned to an
interface in the invalidation lifetime

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of usual sense. An interface discards
received packets addressed to a tentative address, but
accepts Neighbor Discover packets related to duplicate
address detection for the tentative address.

invalidation lifetime

preferred address
- indicates the time at which an address no longer
identifies assigned to an interface whose use by upper
layer protocols is unrestricted. Preferred addresses
may be used as the source or set destination address of interfaces.
The invalidation lifetime must be greater than
packets sent from or equal to the deprecation lifetime of the address.

valid interface.

deprecated address
- an An address assigned to an interface whose deprecation lifetime has use is
discouraged, but not yet
expired. forbidden. A deprecated address
- an
should no longer be used as a source address whose deprecation lifetime has expired, in new
communications, but whose invalidation lifetime has not.

invalid packets sent to deprecated address
- an
are delivered as expected. A deprecated address whose invalidation lifetime has
expired. may
continue to be used as a source address in
communications where switching to a preferred address
causes hardship to a specific upper-layer activity
(e.g., an existing TCP connection).

valid address
- a preferred or deprecated address. A valid address may
appear as the source or destination address of a
packet, and the internet routing system is expected to
be able to deliver packets sent to a valid address.

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invalid address
- an address that is not assigned to any interface. A
valid address becomes invalid when its deprecation
lifetime expires. Invalid addresses should not appear
as the destination or source address of a packet. In
the former case, the internet routing system will be
unable to deliver the packet, in the later case the
recipient of the packet will be unable to respond to
it.

preferred lifetime
- the length of time that a valid address is preferred.
When the preferred lifetime expires, the address
becomes deprecated.

valid lifetime
- the length of time an address remains in the valid
state. The valid lifetime must be greater then or equal
to the preferred lifetime. When the valid lifetime
expires, the address becomes invalid.

interface token
- a link-dependent identifier for an interface that is
(at least) unique per link. An example is Stateless address
autoconfiguration combines an interface token with a
prefix to form an address. An IEEE 802
address. hardware address
is an example of a possible interface token. The manner
in which an interface token is created and its length
is link-specific, and is described in the specification
for the particular link type (e.g., [IPv6-ETHER]).

2.1. Requirements

Throughout this document, the words that are used to define the sig-
nificance
significance of the particular requirements are capitalized. These
words are:

MUST
This word or the adjective "REQUIRED" means that the item is an
absolute requirement of this specification.

MUST NOT
This phrase means the item is an absolute prohibition of this
specification.

SHOULD

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This word or the adjective "RECOMMENDED" means that there may exist

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valid reasons in particular circumstances to ignore this item, but
the full impliciations implications should be understood and the case carefully
weighed before choosing a different course.

SHOULD NOT
This phrase means that there may exist valid reasons in particu-
lar particular
circumstances when the listed behavior is acceptable or even
useful, but the full implications should be understood and the case
carefully weighted before implementing any behavior described with
this label.

MAY
This word or the adjective "OPTIONAL" means that this item is truly
optional. One vendor may choose to include the item because a
particular marketplace requires it or because it enhances the
product, for example, another vendor may omit the same item.

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3. CONCEPTUAL MODEL OF HOST BEHAVIOR

Conceptually, a host maintains three data structures: a list of
addresses per interface and two flags. One flag, called the "address
mode" flag, indicates whether the stateful protocol DESIGN GOALS

Stateless autoconfiguration is to be used for
address configuration (possibly in addition to the stateless proto-
col). The other flag, called designed with the "other following goals in
mind:

o Manual configuration mode" flag,
indicates whether the stateful protocol is to be used for configura-
tion of other information besides addresses.

The address list always includes at least one address, individual machines before connecting them
to the host's
link-local address, which network should not be required. Consequently, a mechanism is an address
needed that can only be used in com-
munications between nodes attached allows a host to the link. In addition, the
address list includes any global obtain or site-local create unique addresses for
each of its interfaces. Address autoconfiguration assumes that have
been manually or automatically configured.

Note each
interface can provide a unique identifier for that stateless address autoconfiguration applies only to the
formation of unicast addresses. A node may, however, have anycast and
multicast addresses associated with interface (e.g.,
an interface. "interface token"). In particular, a
host must join the all-nodes multicast address on any multicast
interface, and the solicited-node multicast address corresponding to
each unicast address on any multicast interface.

3.1. Address Configuration

3.1.1. Link-Local Address

On initialization of an interface, a host must form a link-local
address by concatenating a well-known link-local prefix[1] to simplest case, an interface token that is unique per link. The definition
consists of the
tokens used are link-dependent. For example, in the case link's hardware address. An interface token can be
combined with a prefix to form an address.

o Small sites consisting of a host set of machines attached to a single
link that uses IEEE 802 addresses, should not require the token presence of a stateful server or router
as a prerequisite for communicating. Plug-and-play communication
is achieved through the
48-bit IEEE 802 link-layer address use of the interface. Tokens for link-local addresses. Link-local
addresses have a
specific well-known prefix that identifies the (single)
shared link are defined in link-specific IPv6 documents and are
outside the scope of this document.

Note that a host is able to autoconfigure a link-local address

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completely autonomously. In particular, a host can form a link-local
address without which a router present on the link.

3.1.2. Global/Site-Local Address set of nodes attach. A host forms a new global/site-local address whenever a new prefix is
advertised by a router and stateless address configuration is
enabled. The link-
local address is formed by concatenating the network link-local prefix
to the with its
interface token that is unique per link in the same way as a
link-local address described above.

The mechanism used to advertise network prefixes for token.

o A large site with multiple networks and routers should not require
the purposes presence of a stateful address configuration is the same as server. To enable
hosts to generate site-local or global addresses, Router
Advertisements, which are generated by routers, include options
that used in Neighbor Discovery
for list the purposes set of prefix discovery. A router advertises prefix
information periodically and active prefixes on a host uses this information to config-
ure and reconfigure addresses.

3.2. link.

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One of Autoconfiguration October 1995

o Address configuration should facilitate the goals graceful renumbering of IPv6 address autoconfiguration is not only
a site's machines. For example, a site may wish to be
able renumber all of
its nodes when it switches to autoconfigure a list new network service provider.
Renumbering is achieved through the leasing of addresses on initialization of an
interface, but to be able
interfaces and the assignment of multiple addresses to change the address list dynamically.
Note that same
interface. Lease lifetimes provide the link-local address never changes (except possibly on
interface re-initialization). Host mechanism through which a
site phases out old prefixes. The assignment of multiple addresses may need
to change an interface provides for a
number of reasons. For example, if the transition period during which both
a new address assignment scheme is
provider-based, hosts may need to change addresses when hosts change
provider. Hosts may also need to change addresses when they are
disconnected from one link and connected the one being phased out work simultaneously.

o System administrators need the ability to another. Reconfiguration
must not only allow specify whether stateless
autoconfiguration, stateful autoconfiguration, or both should be
used. Router Advertisements include flags specifying which
mechanisms a host to acquire a new address, but must also
allow hosts to time-out an old address.

Current networking protocols have not been designed to maintain
existing communications during should use.

4. PROTOCOL OVERVIEW

This section describes the typical steps that take place when an address change. For example, a TCP
connection will no longer work if one
interface autoconfigures itself. Autoconfiguration of the hosts changes its a link-local
address in the middle normally takes place when an interface is (re)initialized, e.g.
at startup. Autoconfiguration of a connection. Even in a UDP exchange, a host global and site-local addresses and
other parameters is expected to be able to identify itself using done periodically, starting as soon as possible
after an interface has been initialised or enabled for
autoconfiguration.

A node starts the same autoconfiguration process by generating a link-local
address for the length of interface. Before the exchange.

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To minimise disruption caused by an address change, an address is
configured with two lifetimes : a deprecation lifetime and an invali-
dation lifetime. The deprecation lifetime must can be less than or equal
to the invalidation lifetime. Before expiry of used, however, the deprecation life-
time,
node attempts to verify that the "tentative" address is valid and may be used as the source and destina-
tion not already in any communications. At and after expiry of the deprecation
lifetime, but before
use by another node on the invalidation lifetime has expired, link. The node sends out a Neighbor
Solicitation message containing the tentative address as the target. If
another node is considered already using that address, it will return a Neighbor
Advertisement saying so. If another node is also attempting to be deprecated. A deprecated address can
still be used as use the source and destination in packets legitimately,
but
same address, it will send a Neighbor Solicitation for the deprecated address should not be used target as
well. If a source node determines that its tentative link-local address in
new communications if other valid addresses exist is not
unique, autoconfiguration stops and these addresses
have sufficient scope. If no valid addresses manual configuration of sufficient scope
exist, then the deprecated address should still be used. (Note machine
is required.

Once a node ascertains that
there will always be at least one valid address in the tentative address list, is unique, it assigns
it to the link-local address (see below), but interface. At this address is only useful point, the node has IP-level connectivity
with neighboring nodes via its link-local address.

To generate site-local or global addresses, a host listens for communications on Router
Advertisements. To obtain an advertisement quickly, a host sends one or
more Router Solicitations to the local link, all-routers multicast group. If no
Router Advertisement is received, the host assumes that stateful address
autoconfiguration is desired and thus cannot be used in
place invokes an appropriate protocol.

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Router Advertisements contain two flags indicating what type of a deprecated stateful
autoconfiguration (if any) should be performed. A "managed address for non-local link communications).
configuration" flag indicates whether hosts should use stateful
autoconfiguration to obtain addresses. An "other configuration" flag
indicates whether hosts should use stateful autoconfiguration to obtain
additional information (excluding addresses).

Router Advertisements also contain zero or more Prefix Information
options that indicate what type of stateless address becomes invalid when the invalidation lifetime expires.
Such an address must not autoconfiguration
should be used as a source done. It should be noted that the stateless and stateful
address autoconfiguration fields in outgoing com-
munications or accepted as Router Advertisements are processed
independently of one another, and a destination address in incoming communi-
cations. An invalid host may use both stateful and
stateless address is removed from autoconfiguration simultaneously. One Prefix
Information option field, the address list of "autonomous address-configuration flag",
indicates whether or not the
interface.

Note that option even applies to stateless
autoconfiguration. If it does, additional option fields contain a
subnet prefix together with lifetime values indicating how long
addresses created from the deprecation lifetimes prefix remain preferred and invalidation lifetimes of valid.

Routers advertise Router Advertisements periodically. Hosts process the
link-local address are set to infinity. Thus,
information contained in each advertisement as described above.

For safety, all addresses obtained through autoconfiguration should be
tested for uniqueness. In the link-local address
is never deprecated.

The intention case of addresses created through
stateless autoconfig, however, the two lifetimes per uniqueness of an address is to allow system
administrators to specify a graceful transition period during
renumbering. The purpose of
determined primarily by the deprecation time is to indicate to portion of the host to start using another (presumably longer lasting) address
in new communications to minimise formed from an
interface token. Thus, if a node has already verified the risk uniqueness of breaking communications
when
a link-local address, additional addresses created from the old one times out. A system administrator same
interface token need not be tested for uniqueness. In contrast, all
addresses obtained via stateful address autoconfiguration should set the
deprecation period long enough so be
tested for uniqueness individually. To accommodate sites that most, if not all, communica-
tions have switched over to using believe
the new overhead of performing duplicate address by the time detection outweighs its
benefits, the old
one becomes invalid. The length use of the deprecation period will duplicate address detection can be
environment-dependent as it depends on disabled through
the expected length administrative setting of commun-
ications.

The fact that addresses have a deprecation lifetime does not need per-interface configuration flag.

4.1. Site Renumbering

Address leasing facilitates site renumbering by providing a mechanism to
affect
time-out addresses in hosts. At present, the implementation of applications, i.e. an application TCP/IP protocol suite
provides no support for changing endpoint addresses while a TCP
connection is
not expected to react when open. If an end-point address it is using becomes deprecated.
The purpose of the deprecation lifetime is changes, existing
connections break and all communication to help the old address fails. Even
when applications or
networking software use UDP as a transport protocol, addresses must
generally remain the same during a packet exchange.

Distinguishing valid addresses into preferred and deprecated categories
provides a way of indicating to select upper layers that a sufficiently long-lasting source

Expires January 7, 1995 valid address may

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address at the beginning of a new communication. The IP layer is
expected to provide a means for upper layers or applications to
select

become invalid shortly, and future communication using the most appropriate source address given a particular desti-
nation. An application may choose to select will
fail, should the source address
itself address's deprecation lifetime expire before starting a new
communication or may leave the address
unspecified, in which case the upper networking ends. To avoid this scenario, higher layers will should use the
mechanism provided by the IP layer to choose a suitable
preferred address on (assuming one of sufficient scope exists) to increase
the application's behalf.

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4. ROUTER SPECIFICATION

The stateless likelihood that an address autoconfiguration mechanism relies on the pre-
fix discovery mechanism specified in [2] for advertising network pre-
fixes required will remain valid for the formation duration of addresses with site-local or glo-
bal scope.

A prefix the
communication. It is advertised up to system administrators to set appropriate
prefix lifetimes in a Prefix Information option of a Router
Advertisement. Prefix Information includes

1. order to minimize the prefix itself

2. impact of failed communication
when renumbering takes place. The deprecation period should be long
enough that most, if not all, communications are using the prefix length

3. a flag indicating whether new address
at the prefix time an address becomes invalid.

The IP layer is expected to be used for prefix
discovery[2].

4. provide a flag indicating whether the prefix is to be used means for stateless upper layers (including
applications) to select the most appropriate source address autoconfiguration

5. given a
particular destination and possibly other constraints. An application
may choose to select the deprecation lifetime of source address itself before starting a new
communication or may leave the prefix address unspecified, in seconds for which case the pur-
pose of address deprecation

6
upper networking layers will use the invalidation lifetime of mechanism provided by the prefix for IP layer
to choose a suitable address on the purpose of application's behalf.

Detailed address invalidation. This field is also used by prefix
discovery[2].

Router Advertisement processing is specified completely in [2] along
with selection rules are beyond the message formats and configuration variables.

Expires January 7, 1995 [Page 12]

INTERNET-DRAFT Stateless Address Configuration July 1995 scope of this document.

5. HOST PROTOCOL SPECIFICATION

This section specifies host address

Address autoconfiguration behavior is performed on
receiving a Router Advertisement. per-interface basis. For
multihomed hosts, address autoconfiguration is performed independently
on each interface.

5.1. Host Configuration Variables

A host SHOULD MUST allow the following variable to be configured per mul-
ticast for each
multicast interface:

Perform_Addr_Config

AutoConfig If set, the host MUST use either stateless or stateful mechanisms
to configure global or site-local addresses and to acquire other
configuration information as specified autoconfigures itself following the
procedure described in this document.

Default: TRUE

An interface that has

DuplAddrDetect If set, the Perform_Addr_Config flag set is called an
"autoconfigurable interface".

5.2. Message Validation

A host node MUST silently discard any Router Advertisement that does not
specify the validity checks as specified in [2]. An advertisement
that passes these validity checks is called a valid advertisement.

5.3. Router Advertisement Processing

To receive a Router Advertisement, a host joins use the all-nodes multi-
cast address over all multicast-capable interfaces.

Expires January 7, 1995 duplicate detection
procedure (Section 5.4) to verify addresses are
unique before assigning them to an interface.

Default: TRUE

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5.2. Autoconfiguration-Related Variables

A host performs the following address configuration processing when maintains a
valid solicited or unsolicited Router Advertisement is received over
an autoconfigurable interface:

For each valid Router Advertisement:

The host stores the current value number of the Address Mode data structures and then
sets the Address Mode to flags:

ManagedFlag Copied from the value Managed field of the Managed most recently
received Router Advertisement message. The flag (M bit).
If the new value is set, the host MUST use stateful address confi-
guration to configure and maintain
starts out in a list FALSE state.

OtherFlag Copied from the Other field of site-local or global
addresses per interface.

Note that this does not mean that the stateful protocol is neces-
sarily invoked each time a most recently
received Router Advertisement arrives message. The flag
starts out in a FALSE state.

AddressList List of addresses together with their associated
lifetimes. Addresses on the M
bit set. list can be obtained
through stateless or stateful address
autoconfiguration, or some other external mechanism.
AddressList initially contains no entries.

The host uses values of these variables and flags changes over time as the
lifetimes of prefixes (and addresses) expire, new prefixes are learned,
etc.

If system management changes an interface's AutoConfig flag only from TRUE to indicate whether
FALSE, the
stateful protocol is to value of ManagedFlag and OtherFlag MUST be used set to configure addresses. The state-
ful protocol is enabled as soon FALSE, with
any in-progress autoconfiguration activities interrupted as described
below in Section 5.5.3.

5.3. Creation of Link-Local Addresses

A host forms a link-local address whenever an interface is initialized
and the Address Mode changes from
FALSE to TRUE. The protocol AutoConfig flag is disabled as soon as TRUE. (Note that the AutoConfig flag
changes may be
set independently of interface initialization. If the link-local address
has not yet been created when the AutoConfig is changed from TRUE FALSE to FALSE. The actual times
TRUE, it is created at which this time.) An interface is initialized after the proto-
col
following events:

- The interface is invoked, for example, to request initialized at system startup time.

- The interface is reinitialized after a list of addresses temporary interface failure
or
renew after being temporarily disabled by system management.

- The interface attaches to a list of addresses, are specified link for the first time.

A link-local address is formed by prepending the protocol itself.

The host stores well-known link-local
prefix E8::0 [ADDR-ARCH] (of appropriate length) to the current value interface token.

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If the interface token has a length of N bits, the Other Configuration flag
and then sets interface token
replaces the Other Configuration Mode flag to that in right-most N zero bits of the
Router Advertisement (O bit). link-local prefix. If the new value
interface token is set, the host
MUST use stateful more than 118 bits in length, autoconfiguration to acquire other fails
and manual configuration
information besides the address.

The above disclaimer applies here as well. The O bit indicates
whether the host must use the stateful mode to acquire other con-
figuration information. is required.

A link-local address has an infinite preferred and valid lifetime; it is
never timed out.

5.4. Verifying The stateful protocol Uniqueness Of An Address

Duplicate address detection is enabled for this
purpose as soon as performed on an interface only if the Other Configuration Mode changes from FALSE
DuplAddrDetect configuration variable is set to TRUE. The protocol

Duplicate address detection is disabled as soon as the mode changes from
TRUE applied to FALSE. The mode does not indicate the timing of frequency an address once after an
address is created, but before assigning it to an interface, regardless
of acquiring that information. This whether the address is defined obtained through stateful, stateless or manual
configuration. All addresses SHOULD be tested for uniqueness. However,
when stateless address autoconfiguration is used, address uniqueness is
determined solely by the stateful
protocol itself.

For each Prefix-Information extension in interface token, assuming that subnet prefixes
are assigned correctly (i.e., if all of an interface's addresses are
generated from the same token, either all addresses or none of them will
be duplicates). Thus, for a set of addresses formed from the Router Advertisement same
interface token, it is sufficient to check that has the Autonomous flag set:

- If one of the prefix advertised matches addresses is
unique on the prefix link. In such cases, one of those addresses MUST be
verified before any of the addresses can be assigned to an

Expires January 7, 1995 [Page 14]

INTERNET-DRAFT Stateless Address Configuration July 1995

autoconfigured address already in interface.
Normally, the list, then set link-local address would be tested, since it is the
deprecation timer first
address to that be formed.

The procedure for detecting duplicate addresses makes use of Neighbor
Solicitation and Advertisement messages as described below. If a
duplicate address is discovered during the deprecation lifetime speci-
fied in procedure, the extension and interface will
need to be manually configured with a new token, or all IP addresses for
the invalidation timer interface will need to be manually configured. Note that of the invalidation lifetime.

Note method
for detecting duplicates is not completely reliable, and it is possible
that this processing MUST NOT be duplicate addresses will still exist.

An address on which the duplicate address detection procedure is applied
is said to be tentative until the procedure has been completed
successfully. A tentative address is not considered "assigned to an
interface" in the link-
local address. traditional sense. That is, if the well-known link-local prefix
is advertised for some reason (probably a configuration
error), then the prefix should be ignored interface must accept
Neighbor Solicitation and a system
management error logged.

- If Advertisement messages containing the prefix advertised does not match
tentative address in the prefix of Target Address field, but processes such
packets differently from those whose Target Address matches an address
assigned to the interface. Other packets addressed to the tentative
address should be silently discarded.

It should also be noted that duplicate address detection will nearly

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INTERNET-DRAFT IPv6 Stateless Address Autoconfiguration October 1995

always need to be performed before an address already in the list, then form is assigned to an address using this
network prefix and the interface token. Definitions of the
interface token to be used on a specific link are documented
elsewhere. avoid problems that directly result from multiple nodes
using the same addresses. If address resolution is done in parallel with
duplicate address detection, and the prefix advertised address is too short or too long subsequently determined
to form a
128-bit address, given the interface token, be in use by another node, the prefix is
ignored and an error is logged.

Add this node performing duplicate address to
detection may send packets containing the list tentative address that
interfere with the deprecation timer set
to that proper functioning of the deprecation lifetime and other nodes, especially the invalidation
timer to that of
one already using the invalidation lifetime.

Note: The address list should be variable-length. Hosts
should be able to store address.

5.4.1. Message Validation

A node MUST silently discard any Neighbor Solicitation or Neighbor
Advertisement that does not specify the link-local address as well validity checks as all
addresses configured using both specified in
[DISCOVERY]. A solicitation that passes these validity checks is called
a valid solicitation or valid advertisement.

5.4.2. Sending Neighbor Solicitation Messages

Before sending a Neighbor Solicitation, an interface MUST join the stateless all-
nodes multicast address and stateful
modes. If the implementation cannot store all addresses, solicited-node multicast address of the
host should log a system management error.

Note
tentative address. The former insures that if the deprecation lifetime is zero, node receives Neighbor
Advertisements from other nodes already using the address with
that prefix is immediately deprecated. Similarly, if address; the invalida-
tion lifetime is zero, latter
insures that two nodes attempting to use the same address simultaneously
detect each other's presence.

To check an address, a node sends a Neighbor Solicitation with that prefix is immediately
made invalid. (The invalidation lifetime is defined a Target
Address set to be no less
than the deprecation lifetime.) If address being checked. The source of the deprecation lifetime solicitation
is
infinity, set to the unspecified address is never deprecated. Similarly, if and the
invalidation lifetime destination is infinity, set to the
solicited-node multicast address is never invali-
dated. The value of infinity is defined in [2].

An address the target address.

If the Neighbor Solicitation is valid until the deprecation timer expires. A valid
address can first message to be used as sent from an
interface after interface (re)initialization, the node should delay the
message by a source address in all outgoing

Expires January 7, 1995 [Page 15]

INTERNET-DRAFT Stateless Address Configuration July 1995

communications random amount of time between 0 and is accepted
MAX_RTR_SOLICITATION_DELAY as a destination address specified in all
incoming communications.

When [DISCOVERY]. This serves to
alleviate congestion when many nodes start up on the deprecation lifetime of an address expires, link at the address
SHOULD continue to be used same
time, such as after a source address if it power failure, and may help to avoid race
conditions when more than one node is in use in
existing communications, but SHOULD NOT trying to solicit for the same
address at the same time.

There should be used in new communica-
tions if a valid address is available and it has sufficient scope.
The IP layer MUST continue way for a node to accept datagrams destined determine whether a sending
interface loops back packets sent to a
deprecated address since multicast address. Otherwise it
will not be possible for a deprecated address is still defined node to
identify the interface.

An address remains deprecated until its invalidation timer expires
at which point determine whether a solicitation
received on an interface is from itself or from another node with a
duplicate address. This issue is discussed in more detail below.

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INTERNET-DRAFT IPv6 Stateless Address Autoconfiguration October 1995

5.4.3. Receiving Neighbor Solicitation and Advertisement Messages

On receipt of a valid Neighbor Solicitation message on an interface,
node behavior depends on whether the target address becomes invalid and is removed from tentative or not.
If the target address list. An invalid address can no longer be used as a
source address in outgoing communications and is not recognised as
a valid destination address tentative, the solicitation is processed in incoming communications since
the normal way [DISCOVERY]. If the target address is defined tentative,
processing takes place as follows. There are two cases to no longer identify consider.

If the interface.

On initialisation source address of an interface, if a host determines that there
are no IPv6 routers on a link, the solicitation is not the unspecified
address, a host MUST attempt to use stateful
autoconfiguration to acquire addresses and other configuration
information. This node is needed to support networks with no IPv6
routers. The host determines that there are no routers performing address resolution on the
link after startup if no Router Advertisements are heard in address. The
node receiving the
time that it would take to send MAX_ROUTER_SOLICITATIONs and wait
for a response[2]. If a router comes up on solicitation should silently discard the link message and Router
Advertisements begin to be received, a host
MUST start to use
Router Advertisements in the normal way, and, in particular, use
advertisements NOT return a response. Responding to determine whether stateless or stateful address
configuration should be in use.

Note that it is possible resolution requests
for hosts to get a tentative address information
using both stateless and stateful protocols since both may be
enabled at risks polluting the Neighbor Caches of other
nodes should the same time. Even if only stateless address autocon-
figuration mode is enabled, it is still possible for hosts to get
information from multiple sources since multiple routers may already be
advertising prefix information. The rules for handling this is as
follows: hosts accept in use by another node.

If the union source address of all information received using the stateless and stateful protocols. If different sources config-
ure Neighbor Solicitation is the same unspecified
address, then the address solicitation is updated with from a node performing duplicate address
detection. There are two cases to consider. First, the most
recently advertised lifetime.

It solicitation may
have been sent by the receiving node (e.g., the packet was looped back).
Alternatively, another node (with the same hardware address and/or
interface token) is also possible for hosts to contain address information from
different sources, when changing from one mechanism attempting to use the other,
i.e. when changing from stateless mode to stateful mode, and vice

Expires January 7, 1995 [Page 16]

INTERNET-DRAFT Stateless Address Configuration July 1995

versa. address. In this the first
case, the rules are no different from above. If solicitation should be ignored. In the
newly enabled mode second case, the
tentative address is configured a duplicate and should not be used (by either
node).

Determining whether a multicast solicitation was looped back to hand out different addresses
than the mode just disabled, then the host contains the union of
addresses
sender or actually came from both sources until the addresses configured using
the old protocol timeout. another node is implementation-dependent.
If both the old and new modes are con-
figured two interfaces happen to hand out have the same hardware link address, then one
cannot distinguish the address is updated
with two cases by comparing the most recently advertised lifetime. NOTE: The above
assumes that packet contents.
Instead, the stateless and stateful modes implementation must have a good understanding of the same life-
time
interface's multicast loopback semantics.

Expires January 7, 1995 [Page 17]

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6. NODE SPECIFICATION

This section specifies the rules for forming In particular:

- If a link-local address. It
also specifies the protocol to be used Neighbor Solicitation for duplicate address detec-
tion.

6.1. Forming a Link-Local Address

A node MUST have a link-local address. A node forms a link-local tentative address whenever an interface is initialised. The method for forming received
prior to having sent a link-local Neighbor Solicitation, the tentative address
is link-dependent a duplicate.

- If a Neighbor Solicitation has been sent, and an identical one is outside
received, the scope of
this document.

An interface may be initialised or become autoconfigurable after any
of tentative address is a duplicate if the following events:

- The interface is initialized at system startup time.
does not loopback multicast packets.

- The interface In all cases, if more Neighbor Solicitation for the tentative
address are received than have been sent, the tentative address is reinitialized after
a temporary duplicate.

If a Neighbor Advertisement containing the tentative address is received
while performing duplicate address detection, the node MUST disable that
interface
failure or after being temporarily disabled by and log a system manage-
ment.

- The node management error. If no such advertisement
is received within the time specified, the address is re-attached no longer

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INTERNET-DRAFT IPv6 Stateless Address Autoconfiguration October 1995

considered to be tentative and can be assigned to the interface.

If a link after being detached for some
time.

The link-local duplicate address is highly likely to need detected, the node does not respond to be one of the
first events in
solicitation. Instead, it disables the interface initialisation process. Clearly, it
must be formed before any duplicate detection processing is performed
for this address (Section 6.2). In hosts, and logs a link-local address is
also required before system
management error.

5.5. Creation of Global- and Site-Local Addresses

5.5.1. Sending Router Solicitations

Router Advertisements are sent periodically to the all-nodes multicast
address. To obtain an advertisement quickly, a host sends out Router
Solicitations as described in [DISCOVERY].

5.5.2. Absence of Router Advertisements

If a link has no routers, a host MUST use stateful autoconfiguration to
obtain addresses and other configuration information. From the
perspective of autoconfiguration, a link has no routers if no Router
Advertisements are being received. Router Advertisements can be absent
in two scenarios:

- From the time autoconfiguration was last initiated, no Router
Advertisements have been received at all, after having sent Router Solicitation, assuming
Solicitations as described in [DISCOVERY].

- At least one Router Advertisement was received, but enough time has
elapsed since receipt of the
node chooses to do this[2]. This is because a solicitation is only
sent if an last advertisement has not yet that a new one
should have been heard (and hence received. Autoconfiguration does not attempt to
detect this situation.

When a host determines that no non-
link local address can be formed), and routers are present on a link, it sets
the unspecified address cannot
be used value of ManagedFlag and OtherFlag to TRUE, initiating stateful
autoconfiguration as a source address described in Section 5.5.3 (if necessary). If a
router subsequently begins sending Router Solicitation.

6.2. Detecting Duplicate Addresses

The procedure Advertisements, the rules in
Section 5.5.3 insure that hosts process them in the proper way.

5.5.3. Router Advertisement Processing

Autoconfiguration silently ignores Router Advertisement messages
received on interfaces in which the AutoConfig flag is set to detect FALSE.

On receipt of a duplicate address MUST be enabled by
default valid Router Advertisement (as defined in nodes and SHOULD be used.

Expires January 7, 1995 [DISCOVERY]),
a host copies the value of the advertisement's Managed bit into

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INTERNET-DRAFT IPv6 Stateless Address Configuration July Autoconfiguration October 1995

In principle,

ManagedFlag. If the duplicate address detection procedure is applied value of ManagedFlag changes from FALSE to
each new address configured for an interface, whether it be manually
configured or configured automatically using either TRUE, the stateless or
stateful mode. However, if
host should invoke the addresses belonging to an interface
are formed using stateful address autoconfiguration protocol. If
the same interface token (as is value of the case in state-
less ManagedFlag changes from TRUE to FALSE, any activity
related to stateful address autoconfiguration and may should be halted. If the case in other forms
value of confi-
guration), then the flag stays unchanged, no special action takes place. In
particular, a host MUST NOT reinvoke stateful address configuration if
it is only necessary to check that one of already participating in the
addresses stateful protocol as a result of an
earlier advertisement.

An advertisement's Other bit is unique on processed in an analogous manner. A host
copies the link. In value of the stateless mechanism, it is
recommended that Other bit into OtherFlag. If the link-local address be value of
OtherFlag changes from FALSE to TRUE, the address checked for
two reasons. First, it makes host should invoke the implementation simpler, since
stateful autoconfiguration protocol. If the
link-local address is guaranteed value of the OtherFlag
changes from TRUE to always exist in all nodes,
whereas global and site-local FALSE, any activity related to stateful
autoconfiguration for parameters other than addresses are not. Second, in hosts,
there will be less delay in performing duplicate address detection.
Address validation can be done as soon as a link-local address is
formed (this can should be done immediately on initialisation halted.
If the value of an inter-
face), whereas checking a global or site-local address involves wait-
ing until the flag stays unchanged, no special action takes place.
In particular, a host hears a Router Advertisement containing address pre-
fixes, and there MUST NOT reinvoke stateful configuration if it is the possibility that no advertisement will be
heard at all.

The procedure for duplicate address detection uses Neighbor Solicita-
tion and Advertisement messages specified
already participating in [2] to validate an
address the stateful protocol as specified below. Note that before carrying out this pro-
cedure, a node joins result of an earlier
advertisement.

For each Prefix-Information option in the all-nodes multicast address. Also, this
mechanism is not completely reliable, and so it is possible that
duplicate addresses will still exist. Router Advertisement:

a) If a duplicate address is
discovered after carrying out this procedure, the node will need to
be configured with a new token, or if this Autonomous flag is not possible, set, silently ignore the IPv6
addresses will need to be manually configured.

6.2.1. Soliciting Node Behavior

An address is checked for uniqueness only once, when Prefix.

b) If the address prefix is
initially configured.

Once the address link-local prefix, silently ignore the Prefix
Information Option.

c) If the preferred lifetime is configured, greater than the valid lifetime,
silently ignore the Prefix Information Option. A node sends a Neighbor Solicita-
tion with MAY wish to
log a target address containing system management error in this case.

d) If the prefix advertised matches the prefix of an autoconfigured
address to be validated.
The source is already in the list, then set the preferred timer to that of
the unspecified address option's preferred lifetime, and the destination is set the valid lifetime to that
of the solicited-node multicast address. The Source Link Layer
Address extension SHOULD NOT be sent (as it will be ignored option's valid lifetime.

e) If the prefix advertised does not match the prefix of an address
already in the list, then form an address by appending the

Expires January 7, 1995 interface
token to the prefix as follows:

If the sum of the prefix length and interface token length does not

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INTERNET-DRAFT IPv6 Stateless Address Configuration July Autoconfiguration October 1995

destination node[2]). Loopback of

equal 128 bits, the Neighbor Solicitation Prefix Information option MUST NOT be disabled.

NOTE: If the Neighbor Solicitation is the first message ignored. An
implementation MAY wish to be sent
from an interface on interface initialisation, the node should delay log a random amount system management error in this
case. It is the responsibility of time between 0 and MAX_INITIALIZATION_DELAY
seconds before sending the solicitation. This serves system administrator to alleviate
congestion when many nodes start up on insure
that the link at lengths of prefixes contained in Router Advertisements are
consistent with the same time,
such as after length of interface tokens for that link type.

In those cases where a power failure, and helps to avoid race conditions
when more site requires the use of longer prefixes than one node
can be accommodated by the interface token, stateful
autoconfiguration can be used.

If an address is trying formed successfully, the host adds it to
AddressList, initializing its preferred and valid lifetime values
from the Prefix Information option.

5.5.4. Address Lifetime Expiry

A preferred address becomes deprecated when its preferred lifetime
expires. A deprecated address SHOULD continue to solicit for the same be used as a source
address at
the same time. (It is recommended that nodes include some unique
value in the seed existing communications, but SHOULD NOT be used to initialise their pseudo-random number gen-
erators. Note that using only the node token as in new
communications if a unique value current (non-deprecated) address is not available and it
has sufficient scope. The IP layer MUST continue to avoid race conditions since the token cannot be relied
upon accept datagrams
destined to be unique. Although the randomization range a deprecated address since a deprecated address is specified in
units of seconds, still a
valid address for the actual randomly-chosen value should not interface.

An address becomes invalid when its valid lifetime expires. An invalid
address MUST NOT be used as a source address in
units of whole seconds, but rather in units of the highest available
timer resolution.)

If after sending outgoing communications
and MUST NOT be recognized as a solicitation, no Neighbor Advertisement is
received from the target, the node SHOULD retransmit the solicitation
at most every DUPL_ADDR_RETRANS_TIMER seconds until either an adver-
tisement is received or valid destination address for the solicitation has been retransmitted
MAX_DUPL_ADDR_RETRANS times. If an advertisement
interface in incoming communications.

Note that if a Prefix Information option is received with a
target preferred
lifetime of zero, the address with that prefix is immediately
deprecated. Similarly, if the same as advertised valid lifetime is zero, the
address being validated in the time it
takes with that prefix immediately becomes invalid.

5.6. Configuration Consistency

It is possible for hosts to send obtain address information using both
stateless and wait for MAX_DUPL_ADDR_RETRANS solicitations, it
must disable stateful protocols since both may be enabled at the same
time. It is also possible that interface the values of other configuration
parameters such as MTU size and log hop limit are advertised both by a system management error.
router[DISCOVERY] and the stateful protocol. If no
such advertisement the same configuration
information is received within provided using multiple sources, then the time specified, value of this
information should be consistent. However, it is not an error if the address
information is considered detected to be valid.

6.2.2. Solicited Node Behavior

A node is in inconsistent: hosts accept the process union of validating an address when a Neighbor
Solicitation has been sent for the address and no Neighbor Advertise-
ment advertising that address has been
all information received in using the time it takes
to send out MAX_DUPL_ADDR_RETRANS solicitations stateless and wait for an
advertisement (DUPL_ADDR_IGNORE_TIMER seconds).

A node must follow special rules when it receives a Neighbor Solici-
tation for an address that it is in the process of validating. This

Expires January 7, 1995 stateful protocols. If

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INTERNET-DRAFT IPv6 Stateless Address Configuration July Autoconfiguration October 1995

is done to help avoid

different sources configure the race condition where more than same information, then the parameters
are updated with the most recently advertised values.

6. OPEN ISSUES/TODO

o Is duplicate address detection strong enough (we only send one node NS).
Constants OK?

o is
attempting to validate configurability of DuplAddrDetect good enough? Note that:

- One can't assume that all nodes are on the address net at the same any one time, i.e. each node
sends out a Neighbor Solicitation and waits to hear a Neighbor Adver-
tisement for the address, but no node actually sends an advertisement
since the address has
so performing DAD just once or twice does not yet been validated.

The special rules are as follows: When a node guarantee that
there won't be collisions later.

- Turning DuplAddrDetect on/off is difficult in the process of
validating an address and receives practice. It is a Neighbor Solicitation for that
address,
per-host (interface) flag, which means it MUST NOT send any advertisement must be turned off
in response to a solici-
tation for that address. Rather, the node silently discards the sol-
icitation unless the source address each machine. If this is don't by setting a kernel flag and
then having everyone boot the unspecified address. In
the latter case, the first such solicitation same kernel, DAD will be turned
off for all nodes, not just a few.

- it might be nice to turn DuplAddrDetect on/off via RAs, but
that means nodes will delay creating link-local addresses
until they've received an RA or concluded that no routers are
present. This is noted, but
otherwise silently discarded (see NOTE below). Any subsequent such
solicitations cause the node likely to disable delay the interface and log a sys-
tem management error.

NOTE: The above behavior is required because nodes send process longer than
performing DAD. (Ouch.)

- perhaps allow RSs to be sent out Neighbor
Solicitations for their own address with loopback enabled. Thus, a
node will always receive unspecified source
address, in order to solicited RAs with at least one solicitation for its own
address. However, there is no way for "do/don't perform
DAD"?

o Possible Neighbor Discovery Changes

-Should we allow RSs to be sent out with unspecified source
address to allow DAD and the node RSs to determine, be sent in gen-
eral, whether the solicitation comes from itself or another node
since parallel,
rather than sequentially. This would reduce the source impact of the packet is the unspecified address. Hence, the
above rules DAD
delay.

Need to specify that a duplicate address Router Solicitation is sent out when
AutoConfig flag changes from FALSE to TRUE.

o what is detected only if the
node receives more than one solicitation for the address.

Once a node has validated its address, it responds correct language to a Neighbor Sol-
icitation with a Neighbor Advertisement as specified use in [2].

6.2.3. Constants

MAX_INITIALIZATION_DELAY 3 seconds
DUPL_ADDR_RETRANS_TIMER 3 seconds
MAX_DUPL_ADDR_RETRANS 1 transmission

Expires January 7, 1995 talking about an "MAC
address" used as an interface token. Should we use "hardware
address"? "MAC" address? Something else?

o ensure use of "node" vs. "host" is right; autoconfig really applies

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to only hosts, but duplicate address detection wants to be more
general. Also, link-local address can apply to all nodes, not only
hosts.

7. SECURITY CONSIDERATIONS

To be completed.

Expires January 7, 1995 [Page 22]

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8. REFERENCES

[1]

[IPv6-ETHER]
M. Crawford. "A Method for the Transmission of IPv6 Packets over
Ethernet Networks", Internet Draft.

[ADDR-ARCH]
R. Hinden and S. Deering, "Internet Protocol Version (IPv6)
Addressing Architecture", Internet Draft, May 1995, draft-ietf-
ipngwg-addr-arch-02.txt

[2]
ipngwg-addr-arch-03.txt

[DISCOVERY]
T. Narten, E. Nordmark and W. A. Simpson, "IPv6 Neighbor
Discovery", "Neighbor Discovery
for IP Version 6 (IPv6)", Internet Draft, July September 1995, <draft-ietf-ipngwg-
discovery-01.txt>
<draft-ietf-ipngwg-discovery-02.txt>

Acknowledgements

The author authors would like to thank the members of both the IPNG and
ADDRCONF working groups for their input. In particular, thanks to Jim
Bound, Steve Deering, Erik Nordmark and Bill Simpson.

Author's Addresses Erik Nordmark.

AUTHORS' ADDRESSES

draft-ietf-addrconf-ipv6-auto-04.txt [Page 20]

INTERNET-DRAFT IPv6 Stateless Address Autoconfiguration October 1995

Susan Thomson Thomas Narten
Bellcore IBM Corporation
445 South Street P.O. Box 12195
Morristown, NJ 07960
U.S.A.

Phone: Research Triangle Park, NC 27709-2195
USA USA

phone: +1 201-829-4514
Email: phone: +1 919 254 7798
email: set@thumper.bellcore.com

Expires January 7, 1995 email: narten@vnet.ibm.com

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Expires January 7, 1995 [Page 24] 21]

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