draft-ietf-ipv6-router-selection-04.txt   draft-ietf-ipv6-router-selection-05.txt 
IPng Working Group R. Draves IPng Working Group R. Draves
Internet Draft D. Thaler Internet Draft D. Thaler
Document: draft-ietf-ipv6-router-selection-04.txt Microsoft Document: draft-ietf-ipv6-router-selection-05.txt Microsoft
June 15, 2004 August 10, 2004
Default Router Preferences and More-Specific Routes Default Router Preferences and More-Specific Routes
Status of this Memo Status of this Memo
This document is an Internet-Draft and is in full conformance with By submitting this Internet-Draft, I certify that any applicable
all provisions of Section 10 of RFC 2026. patent or other IPR claims of which I am aware have been disclosed,
or will be disclosed, and any of which I become aware will be
disclosed, in accordance with RFC 3668.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet- other groups may also distribute working documents as Internet-
Drafts. Drafts.
Internet-Drafts are draft documents valid for a maximum of six Internet-Drafts are draft documents valid for a maximum of six
months and may be updated, replaced, or obsoleted by other documents months and may be updated, replaced, or obsoleted by other documents
at any time. It is inappropriate to use Internet-Drafts as reference at any time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
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from routing tables. from routing tables.
1. Introduction 1. Introduction
Neighbor Discovery [RFC2461] specifies a conceptual model for hosts Neighbor Discovery [RFC2461] specifies a conceptual model for hosts
that includes a Default Router List and a Prefix List. Hosts send that includes a Default Router List and a Prefix List. Hosts send
Router Solicitation messages and receive Router Advertisement Router Solicitation messages and receive Router Advertisement
messages from routers. Hosts populate their Default Router List and messages from routers. Hosts populate their Default Router List and
Prefix List based on information in the Router Advertisement Prefix List based on information in the Router Advertisement
messages. A conceptual sending algorithm uses the Prefix List to messages. A conceptual sending algorithm uses the Prefix List to
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determine if a destination address is on-link and the Default Router determine if a destination address is on-link and the Default Router
List to select a router for off-link destinations. List to select a router for off-link destinations.
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In some network topologies where the host has multiple routers on In some network topologies where the host has multiple routers on
its Default Router List, the choice of router for an off-link its Default Router List, the choice of router for an off-link
destination is important. In some situations, one router may provide destination is important. In some situations, one router may provide
much better performance than another for a destination. In other much better performance than another for a destination. In other
situations, choosing the wrong router may result in a failure to situations, choosing the wrong router may result in a failure to
communicate. (A later section gives specific examples of these communicate. (A later section gives specific examples of these
scenarios.) scenarios.)
This document describes an optional extension to Neighbor Discovery This document describes an optional extension to Neighbor Discovery
Router Advertisement messages for communicating default router Router Advertisement messages for communicating default router
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We use Router Advertisement messages, instead of some other protocol We use Router Advertisement messages, instead of some other protocol
like RIP [RFC2080], because Router Advertisements are an existing like RIP [RFC2080], because Router Advertisements are an existing
standard, stable protocol for router-to-host communication. standard, stable protocol for router-to-host communication.
Piggybacking this information on existing message traffic from Piggybacking this information on existing message traffic from
routers to hosts reduces network overhead. Neighbor Discovery shares routers to hosts reduces network overhead. Neighbor Discovery shares
with Multicast Listener Discovery the property that they both define with Multicast Listener Discovery the property that they both define
host-to-router interactions, while shielding the host from having to host-to-router interactions, while shielding the host from having to
participate in more general router-to-router interactions. In participate in more general router-to-router interactions. In
addition, RIP is unsuitable because it does not carry route addition, RIP is unsuitable because it does not carry route
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lifetimes so it requires frequent message traffic with greater lifetimes so it requires frequent message traffic with greater
processing overheads. processing overheads.
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The mechanisms specified here are backwards-compatible, so that The mechanisms specified here are backwards-compatible, so that
hosts that do not implement them continue to function as well as hosts that do not implement them continue to function as well as
they did previously. they did previously.
1.1. Conventions used in this document 1.1. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in
this document are to be interpreted as described in [RFC2119]. this document are to be interpreted as described in [RFC2119].
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reachable Time | | Reachable Time |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Retrans Timer | | Retrans Timer |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Options ... | Options ...
+-+-+-+-+-+-+-+-+-+-+-+- +-+-+-+-+-+-+-+-+-+-+-+-
Fields: Fields:
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Prf (Default Router Preference) Prf (Default Router Preference)
2-bit signed integer. Indicates whether or not to prefer 2-bit signed integer. Indicates whether or not to prefer
this router over other default routers. If Router this router over other default routers. If Router
Lifetime is zero, the preference value MUST be set to Lifetime is zero, the preference value MUST be set to
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(00) by the sender and MUST be ignored by the receiver. (00) by the sender and MUST be ignored by the receiver.
If the Reserved (10) value is received, the receiver If the Reserved (10) value is received, the receiver
MUST treat the value as if it were (00). MUST treat the value as if it were (00).
Resvd (Reserved) Resvd (Reserved)
A 3-bit unused field. It MUST be initialized to zero by A 3-bit unused field. It MUST be initialized to zero by
the sender and MUST be ignored by the receiver. the sender and MUST be ignored by the receiver.
Possible Options: Possible Options:
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Prefix (Variable Length) | | Prefix (Variable Length) |
. . . .
. . . .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Fields: Fields:
Type TBD Type TBD
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Length 8-bit unsigned integer. The length of the option Length 8-bit unsigned integer. The length of the option
(including the Type and Length fields) in units of (including the Type and Length fields) in units of
8 octets. The Length field is 1, 2, or 3 depending on 8 octets. The Length field is 1, 2, or 3 depending on
Prefix Length. If Prefix Length is greater than 64, then Prefix Length. If Prefix Length is greater than 64, then
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Length must be 3. If Prefix Length is greater than 0, Length must be 3. If Prefix Length is greater than 0,
then Length must be 2 or 3. If Prefix Length is zero, then Length must be 2 or 3. If Prefix Length is zero,
then Length must be 1, 2, or 3. then Length must be 1, 2, or 3.
Prefix Length Prefix Length
8-bit unsigned integer. The number of leading bits in 8-bit unsigned integer. The number of leading bits in
the Prefix that are valid. The value ranges from 0 to the Prefix that are valid. The value ranges from 0 to
128. The Prefix field is 0, 8, or 16 octets depending on 128. The Prefix field is 0, 8, or 16 octets depending on
Length. Length.
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Discussion: Discussion:
There are several reasons for using a new Route Information Option, There are several reasons for using a new Route Information Option,
instead of using flag bits to overload the existing Prefix instead of using flag bits to overload the existing Prefix
Information Option: Information Option:
1. Prefixes will typically only show up in one or the other kind 1. Prefixes will typically only show up in one or the other kind
of option, not both, so a new option does not introduce of option, not both, so a new option does not introduce
duplication. duplication.
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2. The Route Information Option is typically 16 octets while the 2. The Route Information Option is typically 16 octets while the
Prefix Information Option is 32 octets. Prefix Information Option is 32 octets.
3. Using a new option may improve backwards-compatibility with 3. Using a new option may improve backwards-compatibility with
some host implementations. some host implementations.
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3. Conceptual Model of a Host 3. Conceptual Model of a Host
There are three possible conceptual models for host implementation There are three possible conceptual models for host implementation
of default router preferences and more-specific routes, of default router preferences and more-specific routes,
corresponding to different levels of support. We refer to these as corresponding to different levels of support. We refer to these as
type A, type B, and type C. type A, type B, and type C.
3.1. Conceptual Data Structures for Hosts 3.1. Conceptual Data Structures for Hosts
Type A hosts ignore default router preferences and more-specific Type A hosts ignore default router preferences and more-specific
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done as follows. If the received route's lifetime is zero, the done as follows. If the received route's lifetime is zero, the
route is removed from the Routing Table if present. If a route's route is removed from the Routing Table if present. If a route's
lifetime is non-zero, the route is added to the Routing Table if not lifetime is non-zero, the route is added to the Routing Table if not
present and the route's lifetime and preference is updated if the present and the route's lifetime and preference is updated if the
route is already present. A route is located in the Routing Table route is already present. A route is located in the Routing Table
based on prefix, prefix length, and next-hop router. based on prefix, prefix length, and next-hop router.
For example, suppose hosts receive a Router Advertisement from For example, suppose hosts receive a Router Advertisement from
router X with a Router Lifetime of 100 seconds and Default Router router X with a Router Lifetime of 100 seconds and Default Router
Preference of Medium. The body of the Router Advertisement contains Preference of Medium. The body of the Router Advertisement contains
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a Route Information Option for ::/0 with a Route Lifetime of 200 a Route Information Option for ::/0 with a Route Lifetime of 200
seconds and a Route Preference of Low. After processing the Router seconds and a Route Preference of Low. After processing the Router
Advertisement, a type A host will have an entry for router X in its Advertisement, a type A host will have an entry for router X in its
Default Router List with lifetime 100 seconds. If a type B host Default Router List with lifetime 100 seconds. If a type B host
receives the same Router Advertisement, it will have an entry in its receives the same Router Advertisement, it will have an entry in its
Default Router List for router X with Medium preference and lifetime Default Router List for router X with Medium preference and lifetime
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100 seconds. A type C host will have an entry in its Routing Table 100 seconds. A type C host will have an entry in its Routing Table
for ::/0 -> router X, with Low preference and lifetime 200 seconds. for ::/0 -> router X, with Low preference and lifetime 200 seconds.
A type C host MAY have a transient state, during processing of the A type C host MAY have a transient state, during processing of the
Router Advertisement, in which it has an entry in its Routing Table Router Advertisement, in which it has an entry in its Routing Table
for ::/0 -> router X with Medium preference and lifetime 100 for ::/0 -> router X with Medium preference and lifetime 100
seconds. seconds.
3.2. Conceptual Sending Algorithm for Hosts 3.2. Conceptual Sending Algorithm for Hosts
Type A hosts use the conceptual sending algorithm described in Type A hosts use the conceptual sending algorithm described in
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Cache Entries and redo next-hop determination for destinations Cache Entries and redo next-hop determination for destinations
affected by the Routing Table changes. affected by the Routing Table changes.
3.4. Client Configurability 3.4. Client Configurability
Type B and C hosts MAY be configurable with preference values that Type B and C hosts MAY be configurable with preference values that
override the values in Router Advertisements received. This is override the values in Router Advertisements received. This is
especially useful for dealing with routers which may not support especially useful for dealing with routers which may not support
preferences. preferences.
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3.5. Router Reachability Probing 3.5. Router Reachability Probing
When a host avoids using any non-reachable router X and instead When a host avoids using any non-reachable router X and instead
sends a data packet to another router Y, and the host would have sends a data packet to another router Y, and the host would have
used router X if router X were reachable, then the host SHOULD probe used router X if router X were reachable, then the host SHOULD probe
each such router X's reachability by sending a single Neighbor each such router X's reachability by sending a single Neighbor
Solicitation to that router's address. A host MUST NOT probe a Solicitation to that router's address. A host MUST NOT probe a
router's reachability in the absence of useful traffic that the host router's reachability in the absence of useful traffic that the host
would have sent to the router if it were reachable. In any case, would have sent to the router if it were reachable. In any case,
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these probes MUST be rate-limited to no more than one per minute per these probes MUST be rate-limited to no more than one per minute per
router. router.
This requirement allows the host to discover when router X becomes This requirement allows the host to discover when router X becomes
reachable and to start using router X at that point. Otherwise, the reachable and to start using router X at that point. Otherwise, the
host might not notice router X's reachability and continue to use host might not notice router X's reachability and continue to use
the less-desirable router Y until the next Router Advertisement is the less-desirable router Y until the next Router Advertisement is
sent by X. Note that the router may have been unreachable for sent by X. Note that the router may have been unreachable for
reasons other than being down (e.g., a switch in the middle being reasons other than being down (e.g., a switch in the middle being
down), so it may be up to 30 minutes (the maximum advertisement down), so it may be up to 30 minutes (the maximum advertisement
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4. Router Configuration 4. Router Configuration
Routers should not advertise preferences or routes by default. In Routers should not advertise preferences or routes by default. In
particular, they should not "dump out" their entire routing table to particular, they should not "dump out" their entire routing table to
hosts. Routers MAY have a configuration mode where a filter is hosts. Routers MAY have a configuration mode where a filter is
applied to their routing table to obtain the routes that are applied to their routing table to obtain the routes that are
advertised to hosts. advertised to hosts.
Routers SHOULD NOT send more than 17 Route Information Options in Routers SHOULD NOT send more than 17 Route Information Options in
Router Advertisements per link. This arbitrary bound is meant to Router Advertisements per link. This arbitrary bound is meant to
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reinforce that relatively few and carefully selected routes should reinforce that relatively few and carefully selected routes should
be advertised to hosts. be advertised to hosts.
The preference values (both Default Router Preferences and Route The preference values (both Default Router Preferences and Route
Preferences) should not be routing metrics or automatically derived Preferences) should not be routing metrics or automatically derived
from metrics: the preference values should be configured. from metrics: the preference values should be configured.
The information contained in Router Advertisements may change The information contained in Router Advertisements may change
through actions of system management. For instance, the lifetime or through actions of system management. For instance, the lifetime or
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preference of advertised routes may change, new routes could be preference of advertised routes may change, new routes could be
added, etc. In such cases, the router MAY transmit up to added, etc. In such cases, the router MAY transmit up to
MAX_INITIAL_RTR_ADVERTISEMENTS unsolicited advertisements, using the MAX_INITIAL_RTR_ADVERTISEMENTS unsolicited advertisements, using the
same rules as in [RFC2461]. When ceasing to be an advertising same rules as in [RFC2461]. When ceasing to be an advertising
interface and sending Router Advertisements with a Router Lifetime interface and sending Router Advertisements with a Router Lifetime
of zero, the Router Advertisement SHOULD also set the Route Lifetime of zero, the Router Advertisement SHOULD also set the Route Lifetime
to zero in all Route Information Options. to zero in all Route Information Options.
4.1. Guidance to Administrators 4.1. Guidance to Administrators
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tunnel, and general Internet destinations will be reached via the tunnel, and general Internet destinations will be reached via the
home ISP. Without these mechanisms, the home machine might choose to home ISP. Without these mechanisms, the home machine might choose to
send Internet traffic into the corporate network or corporate send Internet traffic into the corporate network or corporate
traffic into the Internet, leading to communication failure because traffic into the Internet, leading to communication failure because
of the firewall. of the firewall.
It is worth noting that the network administrator setting up It is worth noting that the network administrator setting up
preferences and/or more specific routes in Routing Advertisements preferences and/or more specific routes in Routing Advertisements
typically does not know which kind of nodes (Type A, B, and/or C) typically does not know which kind of nodes (Type A, B, and/or C)
will be connected to its links. This requires that the administrator will be connected to its links. This requires that the administrator
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will need to configure the settings that will work in an optimal will need to configure the settings that will work in an optimal
fashion no matter which kinds of nodes will be attached. fashion no matter which kinds of nodes will be attached.
5. Examples 5. Examples
5.1. Best Router for ::/0 vs Router Least Likely to Redirect 5.1. Best Router for ::/0 vs Router Least Likely to Redirect
The best router for the default route is the router with the best The best router for the default route is the router with the best
route toward the wider Internet. The router least likely to route toward the wider Internet. The router least likely to
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redirect traffic depends on the actual traffic usage. The two redirect traffic depends on the actual traffic usage. The two
concepts can be different when the majority of communication concepts can be different when the majority of communication
actually needs to go through some other router. actually needs to go through some other router.
For example, consider a situation where you have a link with two For example, consider a situation where you have a link with two
routers X and Y. Router X is the best for 2002::/16. (It's your 6to4 routers X and Y. Router X is the best for 2002::/16. (It's your 6to4
site gateway.) Router Y is the best for ::/0. (It connects to the site gateway.) Router Y is the best for ::/0. (It connects to the
native IPv6 Iinternet.) Router X forwards native IPv6 traffic to native IPv6 Internet.) Router X forwards native IPv6 traffic to
router Y; router Y forwards 6to4 traffic to router X. If most router Y; router Y forwards 6to4 traffic to router X. If most
traffic from this site is sent to 2002:/16 destinations, then router traffic from this site is sent to 2002:/16 destinations, then router
X is the one least likely to redirect. X is the one least likely to redirect.
To make type A hosts work well, both routers should advertise To make type A hosts work well, both routers should advertise
themselves as default routers. In particular, if router Y goes down, themselves as default routers. In particular, if router Y goes down,
type A hosts should send traffic to router X to maintain 6to4 type A hosts should send traffic to router X to maintain 6to4
connectivity, so router X as well as router Y needs to be a default connectivity, so router X as well as router Y needs to be a default
router. router.
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::/0 route to router X. ::/0 route to router X.
5.2. Multi-Homed Host and Isolated Network 5.2. Multi-Homed Host and Isolated Network
In another scenario, a multi-homed host is connected to the Internet In another scenario, a multi-homed host is connected to the Internet
via router X on one link and to an isolated network via router Y on via router X on one link and to an isolated network via router Y on
another link. The multi-homed host might have a tunnel into a another link. The multi-homed host might have a tunnel into a
firewalled corporate network, or it might be directly connected to firewalled corporate network, or it might be directly connected to
an isolated test network. an isolated test network.
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In this situation, a type A multi-homed host (which has no default In this situation, a type A multi-homed host (which has no default
router preferences or more-specific routes) will have no way to router preferences or more-specific routes) will have no way to
intelligently choose between the two routers X and Y on its Default intelligently choose between the two routers X and Y on its Default
Router List. Users of the host will see unpredictable connectivity Router List. Users of the host will see unpredictable connectivity
failures, depending on the destination address and the choice of failures, depending on the destination address and the choice of
router. router.
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A multi-homed type C host in this same situation can correctly A multi-homed type C host in this same situation can correctly
choose between routers X and Y, if the routers are configured choose between routers X and Y, if the routers are configured
appropriately. For example, router Y on the isolated network should appropriately. For example, router Y on the isolated network should
advertise a Route Information Option for the isolated network advertise a Route Information Option for the isolated network
prefix. It might not advertise itself as a default router at all prefix. It might not advertise itself as a default router at all
(zero Router Lifetime), or it might advertise itself as a default (zero Router Lifetime), or it might advertise itself as a default
router with Low preference. Router X should advertise itself as a router with Low preference. Router X should advertise itself as a
default router with Medium preference. default router with Medium preference.
6. Security Considerations 6. Security Considerations
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RFC2461, where a malicious node causes a prefix to appear as on-link RFC2461, where a malicious node causes a prefix to appear as on-link
indefinitely, resulting in lack of connectivity if it is not. In indefinitely, resulting in lack of connectivity if it is not. In
contrast, an infinite lifetime in a Route Information Option will contrast, an infinite lifetime in a Route Information Option will
cause router reachability probing to continue indefinitely, but will cause router reachability probing to continue indefinitely, but will
not result in lack of connectivity. not result in lack of connectivity.
[RFC3756] provides more details on the trust models, and there is [RFC3756] provides more details on the trust models, and there is
work in progress in the SEND WG on securing router discovery work in progress in the SEND WG on securing router discovery
messages that will address these problems. messages that will address these problems.
7. Acknowledgments 7. IANA Considerations
Section 2.3 defines a new Neighbor Discovery [RFC2461] option, the
Route Information Option, which has been assigned the value TBD
within the numbering space for IPv6 Neighbor Discovery Option
Formats.
RFC EDITORĘs NOTE (to be removed prior to publication): the IANA is
requested to assign a value for "TBD" in the IPv6 Neighbor Discovery
Option Formats. When the assignment has been made, the RFC Editor
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is asked to replace "TBD" (above in this section, and in section
2.3) with the assigned value and to remove this note.
8. Acknowledgments
The authors would like to acknowledge the contributions of Balash The authors would like to acknowledge the contributions of Balash
Akbari, Steve Deering, Robert Elz, Tony Hain, Bob Hinden, Christian Akbari, Steve Deering, Robert Elz, Tony Hain, Bob Hinden, Christian
Huitema, JINMEI Tatuya, Erik Nordmark, Pekka Savola, Kresimir Huitema, JINMEI Tatuya, Erik Nordmark, Pekka Savola, Kresimir
Segaric, and Brian Zill. The packet diagrams are derived from Segaric, and Brian Zill. The packet diagrams are derived from
Neighbor Discovery [RFC2461]. Neighbor Discovery [RFC2461].
8. Normative References 9. Normative References
[RFC2461] Narten, T., Nordmark, E. and W. Simpson, "Neighbor [RFC2461] Narten, T., Nordmark, E. and W. Simpson, "Neighbor
Discovery for IP Version 6 (IPv6)", RFC 2461, December Discovery for IP Version 6 (IPv6)", RFC 2461, December
1998. 1998.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
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[RFC3775] Johnson, D., Perkins, C. and J. Arkko, "Mobility Support [RFC3775] Johnson, D., Perkins, C. and J. Arkko, "Mobility Support
in IPv6", RFC 3775, June 2004. in IPv6", RFC 3775, June 2004.
9. Informative References 10. Informative References
[RFC3056] Carpenter, B. and K. Moore, "Connection of IPv6 Domains [RFC3056] Carpenter, B. and K. Moore, "Connection of IPv6 Domains
via IPv4 Clouds", RFC 3056, February 2001. via IPv4 Clouds", RFC 3056, February 2001.
[RFC2983] Gilligan, R. and E. Nordmark, "Transition Mechanisms for [RFC2983] Gilligan, R. and E. Nordmark, "Transition Mechanisms for
IPv6 Hosts and Routers", RFC 2893, August 2000. IPv6 Hosts and Routers", RFC 2893, August 2000.
[RFC2080] Malkin, G. and R. Minnear, "RIPng for IPv6", RFC 2080, [RFC2080] Malkin, G. and R. Minnear, "RIPng for IPv6", RFC 2080,
January 1997. January 1997.
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Microsoft Microsoft
One Microsoft Way One Microsoft Way
Redmond, WA 98052 Redmond, WA 98052
Phone: +1 425 703 8835 Phone: +1 425 703 8835
Email: dthaler@microsoft.com Email: dthaler@microsoft.com
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Full Copyright Statement Full Copyright Statement
Copyright (C) The Internet Society (2004). All Rights Reserved. Copyright (C) The Internet Society (2004). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and
This document and translations of it may be copied and furnished to except as set forth therein, the authors retain all their rights.
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