ISIS WG
Internet Draft                                    Jean-Philippe Vasseur
                                                        Stefano Previdi
                                                          Cisco Systems

   Proposed Status : Standard
Document: draft-ietf-isis-link-attr-02.txt
Expires: April 2007                                        October 2006

              Definition of an IS-IS Link Attribute sub-TLV

                     draft-ietf-isis-link-attr-01.txt

                   draft-ietf-isis-link-attr-02.txt

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Abstract

   This document defines a sub-TLV called "Link-attributes" carried
   within the TLV 22 and used to flood some link characteristics.

Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and "OPTIONAL" in
   this document are to be interpreted as described in RFC-2119 [i]. [RFC].

Table of contents

   1. Introduction...................................................2 Introduction ..................................................2
   2. Link-attributes sub-TLV format.................................2 format ................................2
   3. Interoperability with routers non supporting this capability...3 capability ..3
   4. Security considerations........................................3 considerations .......................................3
   5. IANA considerations............................................3 considerations ...........................................3
   6. Intellectual Property Considerations...........................3 Considerations ..........................3
   7. Acknowledgments................................................4 Acknowledgments ...............................................4
   8. References.....................................................4 References ....................................................4
   8.1 Normative references.......................................4 references .........................................4
   8.2 Informative references.....................................4 references .......................................4
   9. Authors' Addresses.............................................5 Addresses ............................................4
   Full Copyright Statement..........................................5 Statement .........................................5

1. Introduction

   [IS-IS] specifies the IS-IS protocol (ISO 10589) with extensions to
   support IPv4 in [IS-IS-IP]. A router advertises one or several Link
   State Protocol data units which are composed of variable length
   tuples called TLVs (Type-Length-Value).

   [IS-IS-TE] defines a set of new TLVs whose aims are to add more
   information about links characteristics, increase the range of IS-IS
   metrics and optimize the encoding of IS-IS prefixes.

   This document defines a new sub-TLV named "Link-attributes" carried
   within the extended IS reachability TLV (type 22) specified in [IS-
   IS-TE].
   [IS-IS-TE].

2. Link-attributes sub-TLV format

   The link-attribute sub-TLV is carried within the TLV 22 and has a
   format identical to the sub-TLV format used by the Traffic
   Engineering Extensions for IS-IS [IS-IS-TE]: 1 octet of sub-type, 1
   octet of length of the value field of the sub-TLV followed by the
   value field field, in this case, a 16 bit flags field.

   The Link-attribute sub-type is 19 (to be assigned by IANA) and has a
   length of 2 octets.

   This sub-TLV is OPTIONAL and MAY appear at most once for a single IS
   neighbor. If a received LSP contains more than one Link-Attribute
   Sub-TLV, an implementation MAY decide to consider only the first
   encountered instance.

   The following bits are defined:

   Local Protection Available (0x01). When set, this indicates that the
   link is protected by means of some local protection mechanism (e.g
   [FRR]).

   Link excluded from local protection path (0x02). When set, this link
   SHOULD not be included in any computation of a repair path by any
   other router in the routing area. The triggers for setting up this
   bit are out of the scope of this document.

   Such link characteristics has several applications such as
   constrained shortest path computation for a Traffic Engineering Label
   Switched (TE LSP) path or the triggering of specific actions in the
   context of IS-IS SPF computation.

   Local maintenance required (0x04). When set, this indicates that the
   link will be put out of service and will consequently be shortly
   unavailable. The set of actions triggered by other nodes is out of
   the scope of this document. An example of the usage of this bit is
   provided in [GR-SHUT].

3. Interoperability with routers non supporting this capability

   A router not supporting the link-attribute sub-TLV MUST just
   silently ignore this sub-TLV.

   Where the information in the link attributes sub-TLV is used to
   affect the IS-IS SPF calculation, additional information indicating
   which routers are using this information is required to insure such
   usage does not result in loops or black holes. How this additional
   information is conveyed is outside the scope of this document.

4. Security considerations

   No new security issues are raised in this document.

5. IANA considerations

   IANA will assign a new codepoint for the link-attribute sub-TLV
   defined in this document and carried within TLV 22. Suggested value
   is 19 (to be assigned by IANA).

6. Intellectual Property Considerations

   The IETF takes no position regarding the validity or scope of any
   Intellectual Property Rights or other rights that might be claimed
   to pertain to the implementation or use of the technology described
   in this document or the extent to which any license under such
   rights might or might not be available; nor does it represent that
   it has made any independent effort to identify any such rights.
   Information on the procedures with respect to rights in RFC
   documents can be found in BCP 78 and BCP 79.

   Copies of IPR disclosures made to the IETF Secretariat and any
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   attempt made to obtain a general license or permission for the use
   of such proprietary rights by implementers or users of this
   specification can be obtained from the IETF on-line IPR repository
   at http://www.ietf.org/ipr.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights that may cover technology that may be required to implement
   this standard. Please address the information to the IETF at ietf-
   ipr@ietf.org.
   ietf-ipr@ietf.org.

7. Acknowledgments

   The authors would like to thank Mike Shand and Les Ginsberg for
   their useful comments.

8. References

8.1 Normative references

   [RFC] Bradner, S., "Key words for use in RFCs to Indicate
   Requirement Levels," RFC 2119.

   [IS-IS] "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.

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

   [IS-IS-TE] H. Smit, T. Li, "IS-IS extensions for traffic
   engineering", RFC 3784.

8.2 Informative references

   [FRR] Ping Pan, et al, "Fast Reroute Extensions to RSVP-TE for LSP
   Tunnels", draft-ietf-mpls-rsvp-lsp-fastreroute-07.txt. Work in
   progress.

   [GR-SHUT], Z. Ali et al, "Graceful Shutdown in MPLS Traffic
   Engineering Networks", draft-ali-ccamp-mpls-graceful-shutdown-01.txt.
   Work in progress. RFC 4090, May 2005.

9. Authors' Addresses

   Jean-Philippe Vasseur
      CISCO
   Cisco Systems, Inc.
      300 Beaver Brook
   1414 Massachusetts Avenue
   Boxborough, MA 01719
   USA
   Email: jpv@cisco.com

   Stefano Previdi
      CISCO
   Cisco Systems, Inc.
   Via Del Serafico 200
   00142 - Roma
   ITALY
   Email: sprevidi@cisco.com

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