[Search] [txt|pdf|bibtex] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits]

Versions: 00 01 02 03 04 05 06 07 rfc5308                               
Internet Engineering Task Force                       Christian E. Hopps
INTERNET-DRAFT                                      NextHop Technologies
Expires September 2001                                      2 April 2001

                        Routing IPv6 with IS-IS

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   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

   The list of Internet-Draft Shadow Directories can be accessed at

Copyright Notice

   Copyright (C) The Internet Society (2001).  All Rights Reserved.

Expires September 2001                                         [Page 1]

Draft                    Routing IPv6 with IS-IS              April 2001


   This draft specifies a method for exchanging IPv6 routing information
   using the IS-IS routing protocol [0].  The method utilizes the same
   mechanisms described in RFC 1195 [1].  This is accomplished by adding
   2 new TLVs and defining their use.  These new TLVs are patterned from
   the ones described in "IS-IS extensions for Traffic Engineering" [2].

   Just as in RFC 1195 [1] with IPv4 and OSI, this method allows one to
   route both IPv4 and IPv6 using a single intra-domain routing

1.  Terms

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

2.  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 [1] 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].

3.  IPv6 Reachability TLV

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

   [1] 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.

Expires September 2001                                         [Page 2]

Draft                    Routing IPv6 with IS-IS              April 2001

   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

        4 octets of metric information
        1 octet of control information
             1 bit of up/down information
             1 bit indicating external origination
                  (e.g., from another routing protocol)
             1 bit indicating the existence of sub-TLVs
             5 reserved bits which must be zero and ignored
        1 octet of prefix length
        0-16 octets of prefix
        0-249 optional octets of sub-TLVs, if present consisting of
             1 octet of length of sub-TLVs
             0-248 octets of sub-TLVs

   This structure may appear any number of times (including none) within
   the TLV.

   As is described in [2], "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 1."

   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 optional 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

   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)

Expires September 2001                                         [Page 3]

Draft                    Routing IPv6 with IS-IS              April 2001

   Just as in [2], 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

4.  IPv6 Interface Address TLV

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

   This TLV maps directly to [1]'s "IP Interface Address" TLV.  We
   necessarily modify the contents to be 0-15 16 octet IPv6 interface
   addresses instead of 0-63 4 octet IPv4 interface address.

   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

5.  IPv6 NLPID

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

   As with [1] and IPv4, if the IS supports IPv6 routing using IS-IS, it
   must advertise this in the "NLPID" TLV by adding the IPv6 NLPID.

6.  Operation

   We utilize the same changes to [1] as made in [2] for the processing
   of prefix information.  These changes are both related to the SPF

   Since the metric space has been extended we need to redefine the
   MAX_PATH_METRIC (1023) from the original specification in [1].  This
   new value MAX_V6_PATH_METRIC is the same as in [2] (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

Expires September 2001                                         [Page 4]

Draft                    Routing IPv6 with IS-IS              April 2001

   as follows (from best to worst).

        1. Level 1 up prefix
        2. Level 2 up prefix
        3. Level 2 down prefix
        4. Level 1 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.

7.  Implementations

   An implementation of this draft has been completed in GateD.

8.  Security Considerations

   This document raises no new security considerations.

9.  References

[0]  "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)", ISO
     10589, 1992.

[1]  Callon, R., "Use of OSI IS-IS for Routing in TCP/IP and Dual
     Environments", RFC 1195, December 1990.

[2]  Smit, H., and T. Li, "IS-IS extensions for Traffic Engineering",
     Work in Progress, May 1999.

10.  Author's Address

     Christian E. Hopps
     NextHop Technologies, Inc.
     517 W. William Street,
     Ann Arbor, MI  48103-4943
     Phone: +1 734 936 0291

Expires September 2001                                         [Page 5]

Draft                    Routing IPv6 with IS-IS              April 2001

     Email: chopps@nexthop.com

11.  Full Copyright Statement

   Copyright (C) The Internet Society 2000. All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the  purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an

Expires September 2001                                         [Page 6]