ISIS WG
Internet Draft Jean-Philippe Vasseur
Stefano Previdi
Cisco Systems
Proposed Status : Standard
Expires: November 2005 May 2005
Definition of an IS-IS Link Attribute sub-TLV
draft-ietf-isis-link-attr-01.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].
draft-ietf-isis-link-attr-01.txt May 2005
Table of contents
1. Introduction...................................................2
2. Link-attributes sub-TLV format.................................2
3. Interoperability with routers non supporting this capability...3
4. Security considerations........................................3
5. IANA considerations............................................3
6. Intellectual Property Considerations...........................3
7. Acknowledgments................................................4
8. References.....................................................4
8.1 Normative references.......................................4
8.2 Informative references.....................................4
9. Authors' Addresses.............................................5
Full Copyright 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].
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 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.
The following bits are defined:
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draft-ietf-isis-link-attr-01.txt May 2005
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
Vasseur and Previdi [Page 3]
draft-ietf-isis-link-attr-01.txt May 2005
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
assurances of licenses to be made available, or the result of an
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.
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.
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draft-ietf-isis-link-attr-01.txt May 2005
9. Authors' Addresses
Jean-Philippe Vasseur
CISCO Systems, Inc.
300 Beaver Brook
Boxborough, MA 01719
USA
Email: jpv@cisco.com
Stefano Previdi
CISCO Systems, Inc.
Via Del Serafico 200
00142 - Roma
ITALY
Email: sprevidi@cisco.com
Full Copyright Statement
Copyright (C) The Internet Society (2005). This document is subject
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