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Routing IPv6 with IS-IS

The information below is for an old version of the document that is already published as an RFC.
Document Type
This is an older version of an Internet-Draft that was ultimately published as RFC 5308.
Author Christian Hopps
Last updated 2015-10-14 (Latest revision 2007-10-05)
RFC stream Internet Engineering Task Force (IETF)
Intended RFC status Proposed Standard
Additional resources Mailing list discussion
Stream WG state (None)
Document shepherd (None)
IESG IESG state Became RFC 5308 (Proposed Standard)
Action Holders
Consensus boilerplate Unknown
Telechat date (None)
Responsible AD Ross Callon
Send notices to (None)
IS-IS for IP Internets                                          C. Hopps
Internet-Draft                                             Cisco Systems
Intended status: Standards Track                         October 4, 2007
Expires: April 6, 2008

                        Routing IPv6 with IS-IS

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
   have been or will be disclosed, and any of which he or she becomes
   aware will be disclosed, in accordance with Section 6 of BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at

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   This Internet-Draft will expire on April 6, 2008.

Copyright Notice

   Copyright (C) The IETF Trust (2007).


   This draft specifies a method for exchanging IPv6 routing information
   using the IS-IS routing protocol.  The described method utilizes 2
   new TLVs, a reachability TLV and an interface address TLV to
   distribute the necessary IPv6 information throughout a routing
   domain.  Using this method one can route IPv6 along with IPv4 and OSI
   using a single intra-domain routing protocol.

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Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

1.  Overview

   IS-IS is an extendible intra-domain routing protocol.  Each router in
   the routing domain issues an LSP that contains information pertaining
   to that router.  The LSP contains typed variable length data often
   referred to as TLVs (type-length-values).  We extend the protocol
   with 2 new TLVs to carry information required to perform IPv6

   In [RFC1195] a method is described to route both OSI and IPv4.  We
   utilize this same method with some minor changes to allow for IPv6.
   To do so we must define 2 new TLVs, namely "IPv6 Reachability" and
   "IPv6 Interface Address" and a new IPv6 protocol identifier.  In our
   new TLVs we utilize the extended metrics and up/down semantics of

2.  IPv6 Reachability TLV

   The "IPv6 Reachability" TLV is TLV type 236 (0xEC).

   [RFC1195] defines 2 Reachability TLVs, "IP Internal Reachability
   Information" and "IP External Reachability Information".  We provide
   the equivalent IPv6 data with the "IPv6 Reachability" TLV and an
   "external" bit.

   The "IPv6 Reachability" TLV describes network reachability through
   the specification of a routing prefix, metric information, a bit to
   indicate if the prefix is being advertised down from a higher level,
   a bit to indicate if the prefix is being distributed from another
   routing protocol and OPTIONALLY the existence of Sub-TLVs to allow
   for later extension.  This data is represented by the following

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   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   |  Type = 236   |    Length     |          Metric ..            |
   |          .. Metric            |U|X|S| Reserve |  Prefix Len   |
   |  Prefix ...
   |Sub-TLV Len(*) | Sub-TLVs(*) ...
   * - if present

   U - up/down bit
   X - external original bit
   S - subtlv present bit

   The above IPv6 Reachability TLV MAY appear any number of times
   (including none) within an LSP.  Link-local prefixes MUST NOT be
   advertised using this TLV.

   As is described in [RFC2784], "the up/down bit is set to 0 when a
   prefix is first injected into IS-IS.  If a prefix is redistributed
   from a higher level to a lower level (e.g., level two to level one),
   the bit SHALL be set to 1 to indicate that the prefix has travelled
   down the hierarchy.  If a prefix is redistributed from an area to
   another area at the same level then the up/down bit SHALL be set to

   If the prefix was distributed into IS-IS from another routing
   protocol the external bit SHALL be set to 1.  This information is
   useful when distributing prefixes from IS-IS to other protocols.

   If the Sub-TLV bit is set to 0 then the octets of Sub-TLVs are not
   present.  Otherwise the bit is 1 and the octet following the prefix
   will contain the length of the Sub-TLV portion of the structure.

   The prefix is "packed" in the data structure.  That is, only the
   required number of octets of prefix are present.  This number can be
   computed from the prefix length octet as follows:

   prefix octets = integer of ((prefix length + 7) / 8)

   Just as in [RFC2784], if a prefix is advertised with a metric larger
   than MAX_V6_PATH_METRIC (0xFE000000), this prefix MUST not be
   considered during the normal SPF computation.  This will allow
   advertisement of a prefix for purposes other than building the normal
   IPv6 routing table.

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   If Sub-TLVs are present they have the same form as normal TLVs as
   shown below.

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   |      Type     |    Length     |         Value(*) ..
   * - if present

   Length indicates how many octets of value are present and can be 0.

3.  IPv6 Interface Address TLV

   The "IPv6 Interface Address" TLV is TLV type 232 (0xE8).

   TLV 232 maps directly to "IP Interface Address" TLV in [RFC1195] .
   We necessarily modify the contents to be 0-15 16 octet IPv6 interface
   addresses instead of 0-63 4 octet IPv4 interface address.

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   |  Type = 232   |    Length     |   Interface Address 1(*) ..   |
   |                  .. Interface Address 1(*) ..                 |
   |                  .. Interface Address 1(*) ..                 |
   |                  .. Interface Address 1(*) ..                 |
   |   Interface Address 1(*) ..   |   Interface Address 2(*) ..
   * - if present

   We further restrict the semantics of this TLV depending on where it
   is advertised.  For Hello PDUs the "Interfaces Address" TLV MUST
   contain only the link-local IPv6 addresses assigned to the interface
   which is sending the Hello.  For LSPs the "Interfaces Address" TLVs
   MUST contain only the non-link-local IPv6 addresses assigned to the

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4.  IPv6 NLPID

   The value of the IPv6 NLPID is 142 (0x8E).

   As with [RFC1195] and IPv4, if the IS supports IPv6 routing using
   IS-IS, it MUST advertise this in the "NLPID" TLV by adding the IPv6

5.  Operation

   We utilize the same changes to [RFC1195] as made in [RFC2784] for the
   processing of prefix information.  These changes are both related to
   the SPF calculation.

   Since the metric space has been extended we need to redefine the
   MAX_PATH_METRIC (1023) from the original specification in [RFC1195].
   This new value MAX_V6_PATH_METRIC is the same as in [RFC2784]
   (0xFE000000).  If during the SPF a path metric would exceed
   MAX_V6_PATH_METRIC it SHALL be considered to be MAX_V6_PATH_METRIC.

   The order of preference between paths for a given prefix MUST be
   modified to consider the up/down bit.  The new order of preference is
   as follows (from best to worst).

   1.  Level 1 up prefix

   2.  Level 2 up prefix

   3.  Level 2 down prefix

   4.  Level 2 down prefix

   If multiple paths have the same best preference then selection occurs
   based on metric.  Any remaining multiple paths SHOULD be considered
   for equal-cost multi-path routing if the router supports this,
   otherwise the router can select any one of the multiple paths.

6.  IANA Considerations

   IANA is requested to update the IS-IS codepoint registry
   ( so that TLV
   codes 232 and 236 refer to this document's RFC number.

   IANA is additionally requested to create the following new code-point
   registry for Sub-TLVs of TLV 236.  The range of values for Type is
   0-255.  Allocations within the registry require documentation of the

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   use and approval by the Designated Expert assigned by the IESG
   [RFC2434].  All code-points are currently unassigned.

   Note to RFC Editor: this section may be removed on publication as an

7.  Security Considerations

   This document raises no new security considerations.  Security
   considerations for the IS-IS protocol are covered in [ISO10589] and
   in [RFC3567].

8.  References

8.1.  Normative References

              "Intermediate System to Intermediate System Intra-Domain
              Routeing Exchange Protocol for use in Conjunction with the
              Protocol for Providing the Connectionless-mode Network
              Service (ISO 8473)", 1992.

   [RFC1195]  Callon, R., "Use of OSI IS-IS for routing in TCP/IP and
              dual environments", RFC 1195, December 1990.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2434]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 2434,
              October 1998.

   [RFC2784]  Farinacci, D., Li, T., Hanks, S., Meyer, D., and P.
              Traina, "Generic Routing Encapsulation (GRE)", RFC 2784,
              March 2000.

   [RFC3567]  Li, T. and R. Atkinson, "Intermediate System to
              Intermediate System (IS-IS) Cryptographic Authentication",
              RFC 3567, July 2003.

8.2.  Informative References

   [RFC3787]  Parker, J., "Recommendations for Interoperable IP Networks
              using Intermediate System to Intermediate System (IS-IS)",
              RFC 3787, May 2004.

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Author's Address

   Christian E. Hopps
   Cisco Systems
   170 W. Tasman Dr.
   San Jose, California  95134


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Full Copyright Statement

   Copyright (C) The IETF Trust (2007).

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