draft-ietf-ipv6-rfc2462bis-00.txt   draft-ietf-ipv6-rfc2462bis-01.txt 
IETF IPv6 Working Group S. Thomson IETF IPv6 Working Group S. Thomson
Internet-Draft Cisco Internet-Draft Cisco
Expires: August 9, 2004 T. Narten Expires: December 13, 2004 T. Narten
IBM IBM
T. Jinmei T. Jinmei
Toshiba Toshiba
H. Soliman H. Soliman
Flarion Technologies Flarion Technologies
February 9, 2004 June 14, 2004
IPv6 Stateless Address Autoconfiguration IPv6 Stateless Address Autoconfiguration
draft-ietf-ipv6-rfc2462bis-00.txt draft-ietf-ipv6-rfc2462bis-01.txt
Status of this Memo Status of this Memo
This document is an Internet-Draft and is in full conformance with This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026. all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
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skipping to change at page 1, line 36 skipping to change at page 1, line 36
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
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This Internet-Draft will expire on August 9, 2004. This Internet-Draft will expire on December 13, 2004.
Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2004). All Rights Reserved. Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract Abstract
This document specifies the steps a host takes in deciding how to This document specifies the steps a host takes in deciding how to
autoconfigure its interfaces in IP version 6. The autoconfiguration autoconfigure its interfaces in IP version 6. The autoconfiguration
process includes creating a link-local address and verifying its process includes creating a link-local address and verifying its
uniqueness on a link, determining what information should be uniqueness on a link, determining what information can be
autoconfigured (addresses, other information, or both), and in the autoconfigured (addresses, other information, or both), and in the
case of addresses, whether they should be obtained through the case of addresses, whether they can be obtained through the stateless
stateless mechanism, the stateful mechanism, or both. This document mechanism, the stateful mechanism, or both. This document defines the
defines the process for generating a link-local address, the process process for generating a link-local address, the process for
for generating global addresses via stateless address generating global addresses via stateless address autoconfiguration,
autoconfiguration, and the Duplicate Address Detection procedure. The and the Duplicate Address Detection procedure. The details of
details of autoconfiguration using the stateful protocol are autoconfiguration using the stateful protocol is specified in RFC
specified elsewhere. 3315 and RFC 3736.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. TERMINOLOGY . . . . . . . . . . . . . . . . . . . . . . . . 4 2. TERMINOLOGY . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1 Requirements . . . . . . . . . . . . . . . . . . . . . . . . 7 2.1 Requirements . . . . . . . . . . . . . . . . . . . . . . . . 7
3. DESIGN GOALS . . . . . . . . . . . . . . . . . . . . . . . . 7 3. DESIGN GOALS . . . . . . . . . . . . . . . . . . . . . . . . 7
4. PROTOCOL OVERVIEW . . . . . . . . . . . . . . . . . . . . . 8 4. PROTOCOL OVERVIEW . . . . . . . . . . . . . . . . . . . . . 8
4.1 Site Renumbering . . . . . . . . . . . . . . . . . . . . . . 10 4.1 Site Renumbering . . . . . . . . . . . . . . . . . . . . . . 10
5. PROTOCOL SPECIFICATION . . . . . . . . . . . . . . . . . . . 11 5. PROTOCOL SPECIFICATION . . . . . . . . . . . . . . . . . . . 11
5.1 Node Configuration Variables . . . . . . . . . . . . . . . . 11 5.1 Node Configuration Variables . . . . . . . . . . . . . . . . 11
5.2 Autoconfiguration-Related Variables . . . . . . . . . . . . 12 5.2 Autoconfiguration-Related Structures . . . . . . . . . . . . 12
5.3 Creation of Link-Local Addresses . . . . . . . . . . . . . . 12 5.3 Creation of Link-Local Addresses . . . . . . . . . . . . . . 12
5.4 Duplicate Address Detection . . . . . . . . . . . . . . . . 13 5.4 Duplicate Address Detection . . . . . . . . . . . . . . . . 13
5.4.1 Message Validation . . . . . . . . . . . . . . . . . . . . . 14 5.4.1 Message Validation . . . . . . . . . . . . . . . . . . . . . 14
5.4.2 Sending Neighbor Solicitation Messages . . . . . . . . . . . 15 5.4.2 Sending Neighbor Solicitation Messages . . . . . . . . . . . 14
5.4.3 Receiving Neighbor Solicitation Messages . . . . . . . . . . 15 5.4.3 Receiving Neighbor Solicitation Messages . . . . . . . . . . 15
5.4.4 Receiving Neighbor Advertisement Messages . . . . . . . . . 16 5.4.4 Receiving Neighbor Advertisement Messages . . . . . . . . . 16
5.4.5 When Duplicate Address Detection Fails . . . . . . . . . . . 17 5.4.5 When Duplicate Address Detection Fails . . . . . . . . . . . 17
5.5 Creation of Global Addresses . . . . . . . . . . . . . . . . 17 5.5 Creation of Global Addresses . . . . . . . . . . . . . . . . 17
5.5.1 Soliciting Router Advertisements . . . . . . . . . . . . . . 17 5.5.1 Soliciting Router Advertisements . . . . . . . . . . . . . . 17
5.5.2 Absence of Router Advertisements . . . . . . . . . . . . . . 17 5.5.2 Absence of Router Advertisements . . . . . . . . . . . . . . 17
5.5.3 Router Advertisement Processing . . . . . . . . . . . . . . 18 5.5.3 Router Advertisement Processing . . . . . . . . . . . . . . 18
5.5.4 Address Lifetime Expiry . . . . . . . . . . . . . . . . . . 20 5.5.4 Address Lifetime Expiry . . . . . . . . . . . . . . . . . . 20
5.6 Configuration Consistency . . . . . . . . . . . . . . . . . 21 5.6 Configuration Consistency . . . . . . . . . . . . . . . . . 21
5.7 Retaining Configured Addresses for Stability . . . . . . . . 21 5.7 Retaining Configured Addresses for Stability . . . . . . . . 21
6. SECURITY CONSIDERATIONS . . . . . . . . . . . . . . . . . . 21 6. SECURITY CONSIDERATIONS . . . . . . . . . . . . . . . . . . 21
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 22 7. IANA CONSIDERATIONS . . . . . . . . . . . . . . . . . . . . 22
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 22
Normative References . . . . . . . . . . . . . . . . . . . . 22 Normative References . . . . . . . . . . . . . . . . . . . . 22
Informative References . . . . . . . . . . . . . . . . . . . 22 Informative References . . . . . . . . . . . . . . . . . . . 23
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 23 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 23
A. LOOPBACK SUPPRESSION & DUPLICATE ADDRESS DETECTION . . . . . 24 A. LOOPBACK SUPPRESSION & DUPLICATE ADDRESS DETECTION . . . . . 24
B. CHANGES SINCE RFC 1971 . . . . . . . . . . . . . . . . . . . 25 B. CHANGES SINCE RFC 1971 . . . . . . . . . . . . . . . . . . . 26
C. CHANGE HISTORY . . . . . . . . . . . . . . . . . . . . . . . 26 C. CHANGE HISTORY . . . . . . . . . . . . . . . . . . . . . . . 26
D. OPEN ISSUES . . . . . . . . . . . . . . . . . . . . . . . . 27 Intellectual Property and Copyright Statements . . . . . . . 29
Intellectual Property and Copyright Statements . . . . . . . 28
1. Introduction 1. Introduction
This document specifies the steps a host takes in deciding how to This document specifies the steps a host takes in deciding how to
autoconfigure its interfaces in IP version 6. The autoconfiguration autoconfigure its interfaces in IP version 6. The autoconfiguration
process includes creating a link-local address and verifying its process includes creating a link-local address and verifying its
uniqueness on a link, determining what information should be uniqueness on a link, determining what information can be
autoconfigured (addresses, other information, or both), and in the autoconfigured (addresses, other information, or both), and in the
case of addresses, whether they should be obtained through the case of addresses, whether they can be obtained through the stateless
stateless mechanism, the stateful mechanism, or both. This document mechanism, the stateful mechanism, or both. This document defines the
defines the process for generating a link-local address, the process process for generating a link-local address, the process for
for generating global addresses via stateless address generating global addresses via stateless address autoconfiguration,
autoconfiguration, and the Duplicate Address Detection procedure. The and the Duplicate Address Detection procedure. The details of
details of autoconfiguration using the stateful protocol are autoconfiguration using the stateful protocol is specified in RFC
specified elsewhere. 3315 [7] and RFC 3736 [8].
IPv6 defines both a stateful and stateless address autoconfiguration IPv6 defines both a stateful and stateless address autoconfiguration
mechanism. Stateless autoconfiguration requires no manual mechanism. Stateless autoconfiguration requires no manual
configuration of hosts, minimal (if any) configuration of routers, configuration of hosts, minimal (if any) configuration of routers,
and no additional servers. The stateless mechanism allows a host to and no additional servers. The stateless mechanism allows a host to
generate its own addresses using a combination of locally available generate its own addresses using a combination of locally available
information and information advertised by routers. Routers advertise information and information advertised by routers. Routers advertise
prefixes that identify the subnet(s) associated with a link, while prefixes that identify the subnet(s) associated with a link, while
hosts generate an "interface identifier" that uniquely identifies an hosts generate an "interface identifier" that uniquely identifies an
interface on a subnet. An address is formed by combining the two. In interface on a subnet. An address is formed by combining the two. In
the absence of routers, a host can only generate link-local the absence of routers, a host can only generate link-local
addresses. However, link-local addresses are sufficient for allowing addresses. However, link-local addresses are sufficient for allowing
communication among nodes attached to the same link. communication among nodes attached to the same link.
In the stateful autoconfiguration model, hosts obtain interface In the stateful autoconfiguration model, hosts obtain interface
addresses and/or configuration information and parameters from a addresses and/or configuration information and parameters from a
server. Servers maintain a database that keeps track of which DHCPv6 server. Servers maintain a database that keeps track of which
addresses have been assigned to which hosts. The stateful addresses have been assigned to which hosts. The stateful
autoconfiguration protocol allows hosts to obtain addresses, other autoconfiguration protocol allows hosts to obtain addresses, other
configuration information or both from a server. Stateless and configuration information or both from a server. Stateless and
stateful autoconfiguration complement each other. For example, a host stateful autoconfiguration complement each other. For example, a host
can use stateless autoconfiguration to configure its own addresses, can use stateless autoconfiguration to configure its own addresses,
but use stateful autoconfiguration to obtain other information. but use stateful autoconfiguration to obtain other information.
Stateful autoconfiguration for IPv6 is the subject of DHCPv6 [7].
To obtain other configuration information without configuring
addresses in the stateful autoconfiguration model, a subset of DHCPv6
will be used [8]. While the model is called "stateful" here in order
to highlight the contrast to the stateless protocol defined in this
document, the intended protocol is also defined to work in a
stateless fashion. This is based on a result, through operational
experiments, that all known "other" configuration information can be
managed by a stateless server, that is, a server that does not
maintain state of each client that the server provides with the
configuration information.
The stateless approach is used when a site is not particularly The stateless approach is used when a site is not particularly
concerned with the exact addresses hosts use, so long as they are concerned with the exact addresses hosts use, so long as they are
unique and properly routable. The stateful approach is used when a unique and properly routable. The stateful approach is used when a
site requires tighter control over exact address assignments. Both site requires tighter control over exact address assignments. Both
stateful and stateless address autoconfiguration may be used stateful and stateless address autoconfiguration may be used
simultaneously. The site administrator specifies which type of simultaneously. The site administrator specifies which type of
autoconfiguration to use through the setting of appropriate fields in autoconfiguration is available through the setting of appropriate
Router Advertisement messages [5]. fields in Router Advertisement messages [5].
IPv6 addresses are leased to an interface for a fixed (possibly IPv6 addresses are leased to an interface for a fixed (possibly
infinite) length of time. Each address has an associated lifetime infinite) length of time. Each address has an associated lifetime
that indicates how long the address is bound to an interface. When a that indicates how long the address is bound to an interface. When a
lifetime expires, the binding (and address) become invalid and the lifetime expires, the binding (and address) become invalid and the
address may be reassigned to another interface elsewhere in the address may be reassigned to another interface elsewhere in the
Internet. To handle the expiration of address bindings gracefully, an Internet. To handle the expiration of address bindings gracefully, an
address goes through two distinct phases while assigned to an address goes through two distinct phases while assigned to an
interface. Initially, an address is "preferred", meaning that its use interface. Initially, an address is "preferred", meaning that its use
in arbitrary communication is unrestricted. Later, an address becomes in arbitrary communication is unrestricted. Later, an address becomes
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valid address - a preferred or deprecated address. A valid address valid address - a preferred or deprecated address. A valid address
may appear as the source or destination address of a packet, and may appear as the source or destination address of a packet, and
the internet routing system is expected to deliver packets sent to the internet routing system is expected to deliver packets sent to
a valid address to their intended recipients. a valid address to their intended recipients.
invalid address - an address that is not assigned to any interface. A invalid address - an address that is not assigned to any interface. A
valid address becomes invalid when its valid lifetime expires. valid address becomes invalid when its valid lifetime expires.
Invalid addresses should not appear as the destination or source Invalid addresses should not appear as the destination or source
address of a packet. In the former case, the internet routing address of a packet. In the former case, the internet routing
system will be unable to deliver the packet, in the later case the system will be unable to deliver the packet, in the latter case
recipient of the packet will be unable to respond to it. the recipient of the packet will be unable to respond to it.
preferred lifetime - the length of time that a valid address is preferred lifetime - the length of time that a valid address is
preferred (i.e., the time until deprecation). When the preferred preferred (i.e., the time until deprecation). When the preferred
lifetime expires, the address becomes deprecated. lifetime expires, the address becomes deprecated.
valid lifetime - the length of time an address remains in the valid valid lifetime - the length of time an address remains in the valid
state (i.e., the time until invalidation). The valid lifetime must state (i.e., the time until invalidation). The valid lifetime must
be greater then or equal to the preferred lifetime. When the be greater than or equal to the preferred lifetime. When the
valid lifetime expires, the address becomes invalid. valid lifetime expires, the address becomes invalid.
interface identifier - a link-dependent identifier for an interface interface identifier - a link-dependent identifier for an interface
that is (at least) unique per link [4]. Stateless address that is (at least) unique per link [4]. Stateless address
autoconfiguration combines an interface identifier with a prefix autoconfiguration combines an interface identifier with a prefix
to form an address. From address autoconfiguration's perspective, to form an address. From address autoconfiguration's perspective,
an interface identifier is a bit string of known length. The an interface identifier is a bit string of known length. The exact
exact length of an interface identifier and the way it is created length of an interface identifier and the way it is created is
is defined in a separate link-type specific document that covers defined in a separate link-type specific document that covers
issues related to the transmission of IP over a particular link issues related to the transmission of IP over a particular link
type (e.g., IPv6 over Ethernet [2]). In many cases, the identifier type (e.g., IPv6 over Ethernet [2]). Note that the address
will be derived from the interface's link-layer address. architecture [4] also defines the length of the interface
identifiers for some set of addresses, but the two sets of
definitions must be consistent. In many cases, the identifier will
be derived from the interface's link-layer address.
2.1 Requirements 2.1 Requirements
The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD, The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,
SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear in this SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear in this
document, are to be interpreted as described in RFC 2119 [3]. document, are to be interpreted as described in RFC 2119 [3].
3. DESIGN GOALS 3. DESIGN GOALS
Stateless autoconfiguration is designed with the following goals in Stateless autoconfiguration is designed with the following goals in
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Renumbering is achieved through the leasing of addresses to Renumbering is achieved through the leasing of addresses to
interfaces and the assignment of multiple addresses to the same interfaces and the assignment of multiple addresses to the same
interface. Lease lifetimes provide the mechanism through which a interface. Lease lifetimes provide the mechanism through which a
site phases out old prefixes. The assignment of multiple site phases out old prefixes. The assignment of multiple
addresses to an interface provides for a transition period during addresses to an interface provides for a transition period during
which both a new address and the one being phased out work which both a new address and the one being phased out work
simultaneously. simultaneously.
o System administrators need the ability to specify whether o System administrators need the ability to specify whether
stateless autoconfiguration, stateful autoconfiguration, or both stateless autoconfiguration, stateful autoconfiguration, or both
should be used. Router Advertisements include flags specifying are available. Router Advertisements include flags specifying
which mechanisms a host should use. which mechanisms a host can use.
4. PROTOCOL OVERVIEW 4. PROTOCOL OVERVIEW
This section provides an overview of the typical steps that take This section provides an overview of the typical steps that take
place when an interface autoconfigures itself. Autoconfiguration is place when an interface autoconfigures itself. Autoconfiguration is
performed only on multicast-capable links and begins when a performed only on multicast-capable links and begins when a
multicast-capable interface is enabled, e.g., during system startup. multicast-capable interface is enabled, e.g., during system startup.
Nodes (both hosts and routers) begin the autoconfiguration process by Nodes (both hosts and routers) begin the autoconfiguration process by
generating a link-local address for the interface. A link-local generating a link-local address for the interface. A link-local
address is formed by appending the interface's identifier to the address is formed by appending the interface's identifier to the
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Once a node ascertains that its tentative link-local address is Once a node ascertains that its tentative link-local address is
unique, it assigns the address to the interface. At this point, the unique, it assigns the address to the interface. At this point, the
node has IP-level connectivity with neighboring nodes. The remaining node has IP-level connectivity with neighboring nodes. The remaining
autoconfiguration steps are performed only by hosts; the autoconfiguration steps are performed only by hosts; the
(auto)configuration of routers is beyond the scope of this document. (auto)configuration of routers is beyond the scope of this document.
The next phase of autoconfiguration involves obtaining a Router The next phase of autoconfiguration involves obtaining a Router
Advertisement or determining that no routers are present. If routers Advertisement or determining that no routers are present. If routers
are present, they will send Router Advertisements that specify what are present, they will send Router Advertisements that specify what
sort of autoconfiguration a host should do. If no routers are sort of autoconfiguration a host can do. Note that stateful
present, stateful autoconfiguration should be invoked. autoconfiguration may still be available even if no routers are
present.
Routers send Router Advertisements periodically, but the delay Routers send Router Advertisements periodically, but the delay
between successive advertisements will generally be longer than a between successive advertisements will generally be longer than a
host performing autoconfiguration will want to wait [5]. To obtain an host performing autoconfiguration will want to wait [5]. To obtain an
advertisement quickly, a host sends one or more Router Solicitations advertisement quickly, a host sends one or more Router Solicitations
to the all-routers multicast group. Router Advertisements contain to the all-routers multicast group. Router Advertisements contain two
two flags indicating what type of stateful autoconfiguration (if any) flags indicating what type of stateful autoconfiguration (if any) is
should be performed. A "managed address configuration" flag indicates available. A "managed address configuration (M)" flag indicates
whether hosts should use stateful autoconfiguration to obtain whether hosts can use stateful autoconfiguration [7] to obtain
addresses. An "other stateful configuration" flag indicates whether addresses. An "other stateful configuration (O)" flag indicates
hosts should use stateful autoconfiguration to obtain additional whether hosts can use stateful autoconfiguration [8] to obtain
information (excluding addresses). additional information (excluding addresses).
The details of how a host may use the M flags, including any use of
the "on" and "off" transitions for this flag, to control the use of
the stateful protocol for address assignment will be described in a
separate document. Similarly, the details of how a host may use the O
flags, including any use of the "on" and "off" transitions for this
flag, to control the use of the stateful protocol for getting other
configuration information will be described in a separate document.
Router Advertisements also contain zero or more Prefix Information Router Advertisements also contain zero or more Prefix Information
options that contain information used by stateless address options that contain information used by stateless address
autoconfiguration to generate global addresses. It should be noted autoconfiguration to generate global addresses. It should be noted
that the stateless and stateful address autoconfiguration fields in that the stateless and stateful address autoconfiguration fields in
Router Advertisements are processed independently of one another, and Router Advertisements are processed independently of one another, and
a host may use both stateful and stateless address autoconfiguration a host may use both stateful and stateless address autoconfiguration
simultaneously. One Prefix Information option field, the "autonomous simultaneously. One Prefix Information option field, the "autonomous
address-configuration flag", indicates whether or not the option even address-configuration flag", indicates whether or not the option even
applies to stateless autoconfiguration. If it does, additional applies to stateless autoconfiguration. If it does, additional
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indicating how long addresses created from the prefix remain indicating how long addresses created from the prefix remain
preferred and valid. preferred and valid.
Because routers generate Router Advertisements periodically, hosts Because routers generate Router Advertisements periodically, hosts
will continually receive new advertisements. Hosts process the will continually receive new advertisements. Hosts process the
information contained in each advertisement as described above, information contained in each advertisement as described above,
adding to and refreshing information received in previous adding to and refreshing information received in previous
advertisements. advertisements.
For safety, all addresses must be tested for uniqueness prior to For safety, all addresses must be tested for uniqueness prior to
their assignment to an interface. In the case of addresses created their assignment to an interface. The test should individually be
through stateless autoconfiguration, however, the uniqueness of an performed on all addresses obtained manually, via stateless address
address is determined primarily by the portion of the address formed autoconfiguration, or via stateful address autoconfiguration. To
from an interface identifier. Thus, if a node has already verified
the uniqueness of a link-local address, additional addresses created
from the same interface identifier need not be tested individually.
In contrast, all addresses obtained manually or via stateful address
autoconfiguration should be tested for uniqueness individually. To
accommodate sites that believe the overhead of performing Duplicate accommodate sites that believe the overhead of performing Duplicate
Address Detection outweighs its benefits, the use of Duplicate Address Detection outweighs its benefits, the use of Duplicate
Address Detection can be disabled through the administrative setting Address Detection can be disabled through the administrative setting
of a per-interface configuration flag. of a per-interface configuration flag.
To speed the autoconfiguration process, a host may generate its To speed the autoconfiguration process, a host may generate its
link-local address (and verify its uniqueness) in parallel with link-local address (and verify its uniqueness) in parallel with
waiting for a Router Advertisement. Because a router may delay waiting for a Router Advertisement. Because a router may delay
responding to a Router Solicitation for a few seconds, the total time responding to a Router Solicitation for a few seconds, the total time
needed to complete autoconfiguration can be significantly longer if needed to complete autoconfiguration can be significantly longer if
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Autoconfiguration also assumes the presence of the variable Autoconfiguration also assumes the presence of the variable
RetransTimer as defined in RFC 2461 [5]. For autoconfiguration RetransTimer as defined in RFC 2461 [5]. For autoconfiguration
purposes, RetransTimer specifies the delay between consecutive purposes, RetransTimer specifies the delay between consecutive
Neighbor Solicitation transmissions performed during Duplicate Neighbor Solicitation transmissions performed during Duplicate
Address Detection (if DupAddrDetectTransmits is greater than 1), Address Detection (if DupAddrDetectTransmits is greater than 1),
as well as the time a node waits after sending the last Neighbor as well as the time a node waits after sending the last Neighbor
Solicitation before ending the Duplicate Address Detection Solicitation before ending the Duplicate Address Detection
process. process.
5.2 Autoconfiguration-Related Variables 5.2 Autoconfiguration-Related Structures
A host maintains a number of data structures and flags related to
autoconfiguration. In the following, we present conceptual variables
and show how they are used to perform autoconfiguration. The specific
variables are used for demonstration purposes only, and an
implementation is not required to have them, so long as its external
behavior is consistent with that described in this document.
Beyond the formation of a link-local address and using Duplicate Beyond the formation of a link-local address and using Duplicate
Address Detection, how routers (auto)configure their interfaces is Address Detection, how routers (auto)configure their interfaces is
beyond the scope of this document. beyond the scope of this document.
Hosts maintain the following variables on a per-interface basis: A host maintains a list of addresses together with their
ManagedFlag
Copied from the M flag field (i.e., the "managed address
configuration" flag) of the most recently received Router
Advertisement message. The flag indicates whether or not addresses
are to be configured using the stateful autoconfiguration
mechanism. It starts out in a FALSE state.
OtherConfigFlag
Copied from the O flag field (i.e., the "other stateful
configuration" flag) of the most recently received Router
Advertisement message. The flag indicates whether or not
information other than addresses is to be obtained using the
stateful autoconfiguration mechanism. It starts out in a FALSE
state.
In addition, when the value of the ManagedFlag is TRUE, the value
of OtherConfigFlag is implicitly TRUE as well. It is not a valid
configuration for a host to use stateful address autoconfiguration
to request addresses only, without also accepting other
configuration information.
A host also maintains a list of addresses together with their
corresponding lifetimes. The address list contains both corresponding lifetimes. The address list contains both
autoconfigured addresses and those configured manually. autoconfigured addresses and those configured manually.
5.3 Creation of Link-Local Addresses 5.3 Creation of Link-Local Addresses
A node forms a link-local address whenever an interface becomes A node forms a link-local address whenever an interface becomes
enabled. An interface may become enabled after any of the following enabled. An interface may become enabled after any of the following
events: events:
- The interface is initialized at system startup time. - The interface is initialized at system startup time.
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- The interface becomes enabled by system management after having - The interface becomes enabled by system management after having
been administratively disabled. been administratively disabled.
A link-local address is formed by prepending the well-known link- A link-local address is formed by prepending the well-known link-
local prefix FE80::0 [4] (of appropriate length) to the interface local prefix FE80::0 [4] (of appropriate length) to the interface
identifier. If the interface identifier has a length of N bits, the identifier. If the interface identifier has a length of N bits, the
interface identifier replaces the right-most N zero bits of the interface identifier replaces the right-most N zero bits of the
link-local prefix. If the interface identifier is more than 118 bits link-local prefix. If the interface identifier is more than 118 bits
in length, autoconfiguration fails and manual configuration is in length, autoconfiguration fails and manual configuration is
required. Note that interface identifiers will typically be 64-bits required. The length of the interface identifier is defined in a
long and based on EUI-64 identifiers as described in [4]. separate link-type specific document, which should also be consistent
with the address architecture [4] (see Section 2). These documents
will carefully define the length so that link-local addresses can be
autoconfigured on the link.
A link-local address has an infinite preferred and valid lifetime; it
is never timed out.
5.4 Duplicate Address Detection 5.4 Duplicate Address Detection
Duplicate Address Detection is performed on unicast addresses prior Duplicate Address Detection is performed on unicast addresses prior
to assigning them to an interface whose DupAddrDetectTransmits to assigning them to an interface whose DupAddrDetectTransmits
variable is greater than zero. Duplicate Address Detection MUST take variable is greater than zero. Duplicate Address Detection MUST take
place on all unicast addresses, regardless of whether they are place on all unicast addresses, regardless of whether they are
obtained through stateful, stateless or manual configuration, with obtained through stateful, stateless or manual configuration, with
the exception of the following cases: the exception of the following cases:
- Duplicate Address Detection MUST NOT be performed on anycast IP - Duplicate Address Detection MUST NOT be performed on anycast
addresses. addresses.
- Each individual unicast address SHOULD be tested for uniqueness. IP - Each individual unicast address SHOULD be tested for uniqueness.
However, when stateless address autoconfiguration is used, address Note that there are implementations deployed that only perform
uniqueness is determined solely by the interface identifier, Duplicate Address Detection for the link-local address and skip
assuming that subnet prefixes are assigned correctly (i.e., if all the test for the global address using the same interface
of an interface's addresses are generated from the same identifier as that of the link-local address. Whereas this
identifier, either all addresses or none of them will be document does not invalidate such implementations, this kind of
duplicates). Thus, for a set of addresses formed from the same "optimization" is NOT RECOMMENDED, and new implementations MUST
interface identifier, it is sufficient to check that the link- NOT do that optimization. This optimization came from the
local address generated from the identifier is unique on the link. assumption that all of an interface's addresses are generated from
In such cases, the link-local address MUST be tested for the same identifier. However, the assumption does actually not
uniqueness, and if no duplicate address is detected, an stand; new types of addresses have been introduced where the
implementation MAY choose to skip Duplicate Address Detection for interface identifiers are not necessarily the same for all unicast
additional addresses derived from the same interface identifier. addresses on a single interface [10] [11]. Requiring to perform
Duplicate Address Detection for all unicast addresses will make
the algorithm robust for the current and future such special
interface identifiers.
The procedure for detecting duplicate addresses uses Neighbor The procedure for detecting duplicate addresses uses Neighbor
Solicitation and Advertisement messages as described below. If a Solicitation and Advertisement messages as described below. If a
duplicate address is discovered during the procedure, the address duplicate address is discovered during the procedure, the address
cannot be assigned to the interface. If the address is derived from cannot be assigned to the interface. If the address is derived from
an interface identifier, a new identifier will need to be assigned to an interface identifier, a new identifier will need to be assigned to
the interface, or all IP addresses for the interface will need to be the interface, or all IP addresses for the interface will need to be
manually configured. Note that the method for detecting duplicates manually configured. Note that the method for detecting duplicates
is not completely reliable, and it is possible that duplicate is not completely reliable, and it is possible that duplicate
addresses will still exist (e.g., if the link was partitioned while addresses will still exist (e.g., if the link was partitioned while
skipping to change at page 15, line 23 skipping to change at page 15, line 10
To check an address, a node sends DupAddrDetectTransmits Neighbor To check an address, a node sends DupAddrDetectTransmits Neighbor
Solicitations, each separated by RetransTimer milliseconds. The Solicitations, each separated by RetransTimer milliseconds. The
solicitation's Target Address is set to the address being checked, solicitation's Target Address is set to the address being checked,
the IP source is set to the unspecified address and the IP the IP source is set to the unspecified address and the IP
destination is set to the solicited-node multicast address of the destination is set to the solicited-node multicast address of the
target address. target address.
If the Neighbor Solicitation is going to be the first message to be If the Neighbor Solicitation is going to be the first message to be
sent from an interface after interface (re)initialization, the node sent from an interface after interface (re)initialization, the node
should delay joining the solicited-node multicast address by a random SHOULD delay joining the solicited-node multicast address by a random
delay between 0 and MAX_RTR_SOLICITATION_DELAY as specified in RFC delay between 0 and MAX_RTR_SOLICITATION_DELAY as specified in RFC
2461 [5]. This serves to alleviate congestion when many nodes start 2461 [5]. This serves to alleviate congestion when many nodes start
up on the link at the same time, such as after a power failure, and up on the link at the same time, such as after a power failure, and
may help to avoid race conditions when more than one node is trying may help to avoid race conditions when more than one node is trying
to solicit for the same address at the same time. to solicit for the same address at the same time.
Even if the Neighbor Solicitation is not going to be the first
message to be sent, the node SHOULD delay joining the solicited-node
multicast address by a random delay between 0 and
MAX_RTR_SOLICITATION_DELAY if the address being checked is configured
by a router advertisement message sent to a multicast address. The
delay will avoid similar congestion when multiple nodes are going to
configure addresses by receiving a same single multicast router
advertisement.
Note that the delay for joining the multicast address implicitly Note that the delay for joining the multicast address implicitly
means delaying transmission of the corresponding MLD report message means delaying transmission of the corresponding MLD report message
[9]. Since RFC 2710 [9] does not request a random delay to avoid race [12]. Since RFC 2710 [12] does not request a random delay to avoid
conditions, just delaying Neighbor Solicitation would cause race conditions, just delaying Neighbor Solicitation would cause
congestion by the MLD report messages. The congestion would then congestion by the MLD report messages. The congestion would then
prevent MLD-snooping switches from working correctly, and, as a prevent MLD-snooping switches from working correctly, and, as a
result, prevent Duplicate Address Detection from working. The result, prevent Duplicate Address Detection from working. The
requirement to include the delay for the MLD report in this case requirement to include the delay for the MLD report in this case
avoids this scenario. avoids this scenario.
In order to improve the robustness of the Duplicate Address Detection In order to improve the robustness of the Duplicate Address Detection
algorithm, an interface MUST receive and process datagrams sent to algorithm, an interface MUST receive and process datagrams sent to
the all-nodes multicast address or solicited-node multicast address the all-nodes multicast address or solicited-node multicast address
of the tentative address while the delaying period. This does not of the tentative address while the delaying period. This does not
skipping to change at page 17, line 44 skipping to change at line 799
processing described below MUST be enabled by default. processing described below MUST be enabled by default.
5.5.1 Soliciting Router Advertisements 5.5.1 Soliciting Router Advertisements
Router Advertisements are sent periodically to the all-nodes Router Advertisements are sent periodically to the all-nodes
multicast address. To obtain an advertisement quickly, a host sends multicast address. To obtain an advertisement quickly, a host sends
out Router Solicitations as described in RFC 2461 [5]. out Router Solicitations as described in RFC 2461 [5].
5.5.2 Absence of Router Advertisements 5.5.2 Absence of Router Advertisements
If a link has no routers, a host MUST attempt to use stateful Even if a link has no routers, stateful autoconfiguration to obtain
autoconfiguration to obtain addresses and other configuration addresses and other configuration information may still be available,
information. An implementation MAY provide a way to disable the and hosts may want to use the mechanism.
invocation of stateful autoconfiguration in this case, but the
default SHOULD be enabled. From the perspective of
autoconfiguration, a link has no routers if no Router Advertisements
are received after having sent a small number of Router Solicitations
as described in RFC 2461 [5].
5.5.3 Router Advertisement Processing
On receipt of a valid Router Advertisement (as defined in RFC 2461
[5]), a host copies the value of the advertisement's M bit into
ManagedFlag. If the value of ManagedFlag changes from FALSE to TRUE,
and the host is not already running the stateful address
autoconfiguration protocol, the host should invoke the stateful
address autoconfiguration protocol, requesting both address
information and other information. If the value of the ManagedFlag
changes from TRUE to FALSE, the host should continue running the
stateful address autoconfiguration, i.e., the change in the value of
the ManagedFlag has no effect. If the value of the flag stays
unchanged, no special action takes place. In particular, a host MUST
NOT reinvoke stateful address configuration if it is already
participating in the stateful protocol as a result of an earlier
advertisement.
An advertisement's O flag field is processed in an analogous manner.
A host copies the value of the O flag into OtherConfigFlag. If the
value of OtherConfigFlag changes from FALSE to TRUE, the host should
invoke the stateful autoconfiguration protocol, requesting
information (excluding addresses if ManagedFlag is set to FALSE). If
the value of the OtherConfigFlag changes from TRUE to FALSE, the host
should continue running the stateful address autoconfiguration
protocol, i.e., the change in the value of OtherConfigFlag has no
effect. If the value of the flag stays unchanged, no special action
takes place. In particular, a host MUST NOT reinvoke stateful
configuration if it is already participating in the stateful protocol
as a result of an earlier advertisement.
For each Prefix-Information option in the Router Advertisement:
a) If the Autonomous flag is not set, silently ignore the Prefix
Information option.
b) If the prefix is the link-local prefix, silently ignore the
Prefix Information option.
c) If the preferred lifetime is greater than the valid lifetime,
silently ignore the Prefix Information option. A node MAY wish to
log a system management error in this case.
d) If the prefix advertised does not match the prefix of an address
already in the list, and the Valid Lifetime is not 0, form an
address (and add it to the list) by combining the advertised
prefix with the link's interface identifier as follows:
| 128 - N bits | N bits |
+---------------------------------------+------------------------+
| link prefix | interface identifier |
+----------------------------------------------------------------+
e) If the advertised prefix matches the prefix of an autoconfigured
address (i.e., one obtained via stateless or stateful address
autoconfiguration) in the list of addresses associated with the
interface, the preferred lifetime of the address is reset to the
Preferred Lifetime in the received advertisement. The specific
action to perform for the valid lifetime of the address depends on
the Valid Lifetime in the received advertisement and the remaining
time to the valid lifetime expiration of the previously
autoconfigured address. We call the remaining time
"RemainingLifetime" in the following discussion:
1. If the received Valid Lifetime is greater than 2 hours or
greater than RemainingLifetime, set the valid lifetime of the
corresponding address to the advertised Valid Lifetime.
2. If RemainingLifetime is less than or equal to 2 hours, ignore
the Prefix Information option with regards to the valid
lifetime, unless the Router Advertisement from which this
option was obtained has been authenticated (e.g., via IP
security [1]). If the Router Advertisement was authenticated,
the valid lifetime of the corresponding address should be set
to the Valid Lifetime in the received option.
3. Otherwise, reset the valid lifetime of the corresponding
address to two hours.
The above rules address a specific denial of service attack in
which a bogus advertisement could contain prefixes with very small
Valid Lifetimes. Without the above rules, a single unauthenticated
advertisement containing bogus Prefix Information options with
short Valid Lifetimes could cause all of a node's addresses to
expire prematurely. The above rules ensure that legitimate
advertisements (which are sent periodically) will "cancel" the
short Valid Lifetimes before they actually take effect.
Note that the preferred lifetime of the corresponding address is
always reset to the Preferred Lifetime in the received Prefix
Information option, regardless of whether the valid lifetime is
also reset or ignored. The difference comes from the fact that the
possible attack for the preferred lifetime is relatively minor.
Additionally, it is even undesirable to ignore the preferred
lifetime when a valid administrator wants to deprecate a
particular address by sending a short preferred lifetime (and the
valid lifetime is ignored by accident).
5.5.4 Address Lifetime Expiry
A preferred address becomes deprecated when its preferred lifetime
expires. A deprecated address SHOULD continue to be used as a source
address in existing communications, but SHOULD NOT be used to
initiate new communications if an alternate (non-deprecated) address
of sufficient scope can easily be used instead.
Note that the feasibility of initiating new communication using a
non-deprecated address may be an application-specific decision, as
only the application may have knowledge about whether the (now)
deprecated address was (or still is) in use by the application. For
example, if an application explicitly specifies the protocol stack to
use a deprecated address as a source address, the protocol stack must
accept that; the application might request it because that IP address
is used for in higher-level communication and there might be a
requirement that the multiple connections in such a grouping use the
same pair of IP addresses.
IP and higher layers (e.g., TCP, UDP) MUST continue to accept and
process datagrams destined to a deprecated address as normal since a
deprecated address is still a valid address for the interface. In the
case of TCP, this means TCP SYN segments sent to a deprecated address
are responded to using the deprecated address as a source address in
the corresponding SYN-ACK (if the connection would otherwise be
allowed).
An implementation MAY prevent any new communication from using a
deprecated address, but system management MUST have the ability to
disable such a facility, and the facility MUST be disabled by
default.
Other subtle cases should also be noted about source address
selection. For example, the above description does not clarify which
address should be used between a deprecated, smaller-scope address
and a non-deprecated, enough scope address. The details of the
address selection including this case is described in RFC 3484 [8]
and beyond the scope of this document.
An address (and its association with an interface) becomes invalid
when its valid lifetime expires. An invalid address MUST NOT be used
as a source address in outgoing communications and MUST NOT be
recognized as a destination on a receiving interface.
5.6 Configuration Consistency
It is possible for hosts to obtain address information using both
stateless and stateful protocols since both may be enabled at the
same time. It is also possible that the values of other
configuration parameters such as MTU size and hop limit will be
learned from both Router Advertisements and the stateful
autoconfiguration protocol. If the same configuration information is
provided by multiple sources, the value of this information should be
consistent. However, it is not considered a fatal error if
information received from multiple sources is inconsistent. Hosts
accept the union of all information received via the stateless and
stateful protocols. If inconsistent information is learned different
sources, the most recently obtained values always have precedence
over information learned earlier.
5.7 Retaining Configured Addresses for Stability
It is reasonable that implementations that have stable storage retain
their addresses and the preferred and valid lifetimes if the
addresses were acquired using stateless address autoconfiguration.
Assuming the lifetimes used are reasonable, this technique implies
that a temporary outage (less than the valid lifetime) of a router
will never result in the node losing its global address even if the
node were to reboot. This will particularly be useful in "zeroconf"
environments where nodes are configuring their addresses by stateless
address autoconfiguration but all communication is limited within a
single link. In such a case, the failure of a "router" (that provides
the prefix for address configuration) is not significant, but losing
the global addresses might be a pain; it is true that the node can
still use link-local addresses for communication within the link, but
the node may want to use global addresses when possible, especially
when the other nodes use global addresses.
When an implementation tries to reuse a retained address after
rebooting, it MUST first try to obtain Router Advertisements as
described in RFC 2461[5] and use the retained address only after
concluding there are no routers on the link. Additionally, the
implementation MUST run Duplicate Address Detection for the address
under the criteria described in Section 5.4, as though the address
were just configured by stateless address autoconfiguration. The
reason for this is because a different host may have started using
the address while the rebooting host cannot respond to Duplicate
Address Detection from the other host.
6. SECURITY CONSIDERATIONS
Stateless address autoconfiguration allows a host to connect to a
network, configure an address and start communicating with other
nodes without ever registering or authenticating itself with the
local site. Although this allows unauthorized users to connect to
and use a network, the threat is inherently present in the Internet
architecture. Any node with a physical attachment to a network can
generate an address (using a variety of ad hoc techniques) that
provides connectivity.
The use of stateless address autoconfiguration and Duplicate Address
Detection opens up the possibility of several denial of service
attacks. For example, any node can respond to Neighbor Solicitations
for a tentative address, causing the other node to reject the address
as a duplicate. A separate document [10] discusses details about
these attacks. These attacks can be addressed by requiring that
Neighbor Discovery packets be authenticated [1]. However, it should
be noted that [10] points out the use of IP security is not always
feasible depending on network environments.
7. Acknowledgements
The authors would like to thank the members of both the IPNG (which
is now IPV6) and ADDRCONF working groups for their input. In
particular, thanks to Jim Bound, Steve Deering, Richard Draves, and
Erik Nordmark. Thanks also goes to John Gilmore for alerting the WG
of the "0 Lifetime Prefix Advertisement" denial of service attack
vulnerability; this document incorporates changes that address this
vulnerability.
Normative References
[1] Kent, S. and R. Atkinson, "IP Authentication Header", RFC 2402,
November 1998.
[2] Crawford, M., "A Method for the Transmission of IPv6 Packets
over Ethernet Networks", RFC 2464, December 1998.
[3] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", RFC 2119, March 1997.
[4] Hinden, R. and S. Deering, "Internet Protocol Version (IPv6)
Addressing Architecture", RFC 3513, April 2003.
[5] Narten, T., Nordmark, E. and W. Simpson, "Neighbor Discovery for
IP Version 6 (IPv6)", RFC 2461, December 1998.
Informative References
[6] Deering, S., "Host Extensions for IP Multicasting", RFC 1112,
August 1989.
[7] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C. and M.
Carney, "Dynamic Host Configuration Protocol for IPv6
(DHCPv6)", RFC 3315, July 2003.
[8] Draves, R., "Default Address Selection for Internet Protocol
version 6 (IPv6)", RFC 3484, February 2003.
[9] Deering, S., Fenner, W. and B. Haberman, "Multicast Listener
Discovery (MLD) for IPv6", RFC 2710, October 1999.
[10] Nikander, P., Kempf, J. and E. Nordmark, "IPv6 Neighbor
Discovery trust models and threats",
draft-ietf-send-psreq-04.txt (work in progress), October 2003.
[11] Park, S., Madanapalli, S. and O. Rao, "IPv6 DAD Consideration
for 802.11 Environment",
draft-park-ipv6-dad-problem-wlan-00.txt (work in progress),
July 2003.
Authors' Addresses
Susan Thomson
Cisco Systems
EMail: sethomso@cisco.com
Thomas Narten
IBM Corporation
P.O. Box 12195
Research Triangle Park, NC 27709-2195
USA
Phone: +1 919-254-7798
EMail: narten@us.ibm.com
Tatuya Jinmei
Corporate Research & Development Center, Toshiba Corporation
1 Komukai Toshiba-cho, Saiwai-ku
Kawasaki-shi, Kanagawa 212-8582
Japan
Phone: +81 44-549-2230
EMail: jinmei@isl.rdc.toshiba.co.jp
Hesham Soliman
Flarion Technologies
EMail: H.Soliman@flarion.com
Appendix A. LOOPBACK SUPPRESSION & DUPLICATE ADDRESS DETECTION
Determining whether a received multicast solicitation was looped back
to the sender or actually came from another node is implementation-
dependent. A problematic case occurs when two interfaces attached to
the same link happen to have the same identifier and link-layer
address, and they both send out packets with identical contents at
roughly the same time (e.g., Neighbor Solicitations for a tentative
address as part of Duplicate Address Detection messages). Although a
receiver will receive both packets, it cannot determine which packet
was looped back and which packet came from the other node by simply
comparing packet contents (i.e., the contents are identical). In this
particular case, it is not necessary to know precisely which packet
was looped back and which was sent by another node; if one receives
more solicitations than were sent, the tentative address is a
duplicate. However, the situation may not always be this
straightforward.
The IPv4 multicast specification [6] recommends that the service
interface provide a way for an upper-layer protocol to inhibit local
delivery of packets sent to a multicast group that the sending host
is a member of. Some applications know that there will be no other
group members on the same host, and suppressing loopback prevents
them from having to receive (and discard) the packets they themselves
send out. A straightforward way to implement this facility is to
disable loopback at the hardware level (if supported by the
hardware), with packets looped back (if requested) by software. On
interfaces in which the hardware itself suppresses loopbacks, a node
running Duplicate Address Detection simply counts the number of
Neighbor Solicitations received for a tentative address and compares
them with the number expected. If there is a mismatch, the tentative
address is a duplicate.
In those cases where the hardware cannot suppress loopbacks, however,
one possible software heuristic to filter out unwanted loopbacks is
to discard any received packet whose link-layer source address is the
same as the receiving interface's. There is even a link-layer
specification that requires to discard any such packets [11].
Unfortunately, use of that criteria also results in the discarding of
all packets sent by another node using the same link-layer address.
Duplicate Address Detection will fail on interfaces that filter
received packets in this manner:
o If a node performing Duplicate Address Detection discards received
packets having the same source link-layer address as the receiving
interface, it will also discard packets from other nodes also
using the same link-layer address, including Neighbor
Advertisement and Neighbor Solicitation messages required to make
Duplicate Address Detection work correctly. This particular
problem can be avoided by temporarily disabling the software
suppression of loopbacks while a node performs Duplicate Address
Detection, if it is possible to disable the suppression.
o If a node that is already using a particular IP address discards
received packets having the same link-layer source address as the
interface, it will also discard Duplicate Address
Detection-related Neighbor Solicitation messages sent by another
node also using the same link-layer address. Consequently,
Duplicate Address Detection will fail, and the other node will
configure a non-unique address. Since it is generally impossible
to know when another node is performing Duplicate Address
Detection, this scenario can be avoided only if software
suppression of loopback is permanently disabled.
Thus, to perform Duplicate Address Detection correctly in the case
where two interfaces are using the same link-layer address, an
implementation must have a good understanding of the interface's
multicast loopback semantics, and the interface cannot discard
received packets simply because the source link-layer address is the
same as the interfaces. It should also be noted that a link-layer
specification can conflict with the condition necessary to make
Duplicate Address Detection work.
Appendix B. CHANGES SINCE RFC 1971
o Changed document to use term "interface identifier" rather than
"interface token" for consistency with other IPv6 documents.
o Clarified definition of deprecated address to make clear it is OK
to continue sending to or from deprecated addresses.
o Added rules to Section 5.5.3 Router Advertisement processing to
address potential denial-of-service attack when prefixes are
advertised with very short Lifetimes.
o Clarified wording in Section 5.5.4 to make clear that all upper
layer protocols must process (i.e., send and receive) packets sent
to deprecated addresses.
Appendix C. CHANGE HISTORY
Changes since RFC 2462 are:
o Fixed a typo in Section 2.
o Updated references and categorized them into normative and
informative ones.
o Removed redundant code in denial of service protection in Section
5.5.3.
o Clarified that a unicasted NS or NA should be discarded while
performing Duplicate Address Detection.
o Replaced the word "StoredLifetime" with "RemainingLifetime" with a
precise definition to avoid confusion.
o Removed references to site-local and revise wording around the
keyword.
o Added a note about source address selection with regards to
deprecated vs insufficient-scope addresses, etc. Added a reference
to RFC 3484 for further details.
o Clarified what "new communication" means in Section 5.5.4.
o Added a new subsection (5.7) to mention the possibility to use
stable storage to retain configured addresses for stability.
o Revised the Security Considerations section with a refence to the
send requirement document and a note that the use of IP security
is not always feasible.
o Added a note with a reference in Appendix A about the case where a
link-layer filtering conflicts with a condition to make DAD work
correctly.
o Specified that a node performing Duplicate Address Detection delay
joining the solicited-node multicast group, not just delay sending
Neighbor Solicitations, explaining the detailed reason.
o Clarified the reason why the interface should be disabled after an
address duplicate is detected. Also clarified that the interface
may continue to be used if the interface identifier is not based
on the hardware address.
o Clarified that the preferred lifetime for an existing configured
address is always reset to the advertised value by Router
Advertisement.
o Updated the description of interface identifier considering the
latest format.
Appendix D. OPEN ISSUES
Semi-Open Issues (resolutions were proposed, but they may need
further discussions):
o [2462bis issue 271] An implementation may want to use stable
storage for autoconfigured addresses.
o [2462bis issue 274] There is conflict with the Multicast Listener
Discovery specification about random delay for the first packet.
o [2462bis issue 278] Whether a router (not a host) can
autoconfigure itself using the stateless autoconfiguration
protocol may need to be discussed.
Open Issues (resolutions have not been proposed yet):
o [2462bis issue 275] Many DAD related issues have been discussed,
including whether it is okay to omit DAD in some environments or
whether DAD can be replaced with DIID (duplicate interface ID
detection).
o [2462bis issue 277] The semantics of the M/O flags is not very
clear.
1. the text needs to be updated to use RFC 2119 keywords
2. which keywords?
3. what is "the stateful configuration protocol"?
4. if the answer to the previous question is DHCPv6, should this
specification more explicitly reference the configuration-only
version of DHCPv6 in the description of the 'O'flag?
o [2462bis issue 281] It is not very clear whether this document
always require a 64-bit Interface ID.
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