RFC5029

Network Working Group JP. Vasseur Request for Comments: 5029 S. Previdi Category: Standards Track Cisco Systems, Inc

                                                      September 2007

         Definition of an IS-IS Link Attribute Sub-TLV

Status of This Memo

This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited.

Abstract

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

Introduction

[IS-IS] specifies the IS-IS protocol (ISO 10589) with extensions to support IPv4 in RFC1195. A router advertises one or several Link State Protocol data units that are composed of variable length tuples called TLVs (Type-Length-Value).

RFC3784 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 RFC3784.

Terminology

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 RFC2119.

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 (RFC3784): 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 and the link-attribute has a length of 2 octets.

This sub-TLV is OPTIONAL and MUST appear at most once for a single IS neighbor. If a received Link State Packet (LSP) contains more than one Link-Attribute Sub-TLV, an implementation SHOULD 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., RFC4090).

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.

Interoperability with Routers Not Supporting This Capability

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

IANA Considerations

IANA has assigned codepoint 19 for the link-attribute sub-TLV defined in this document and carried within TLV 22.

IANA has created a registry for bit values inside the link-attributes sub-TLV. The initial contents of this registry are as follows

 Value   Name                                 Reference
 -----   ----                                 ---------
 0x1     Local Protection Available           RFC5029
 0x2     Link Excluded from Local Protection  RFC5029

Further values are to be allocated by the Standards Action process defined in RFC2434, with Early Allocation (defined in RFC4020) permitted.

Security Considerations

Any new security issues raised by the procedures in this document depend upon the opportunity for LSPs to be snooped and modified, the ease/difficulty of which has not been altered. As the LSPs may now contain additional information regarding router capabilities, this new information would also become available to an attacker. Specifications based on this mechanism need to describe the security considerations around the disclosure and modification of their information. Note that an integrity mechanism, such as one defined in RFC3567, should be applied if there is high risk resulting from the modification of capability information.

Acknowledgements

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

References

Normative References

[IS-IS] "Intermediate System to Intermediate System Intra-Domain

          Routing Exchange Protocol for use in Conjunction with the
          Protocol for Providing the Connectionless-mode Network
          Service (ISO 8473)", ISO 10589.

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.

RFC3784 Smit, H. and T. Li, "Intermediate System to Intermediate

          System (IS-IS) Extensions for Traffic Engineering (TE)",
          RFC 3784, June 2004.

RFC4020 Kompella, K. and A. Zinin, "Early IANA Allocation of

          Standards Track Code Points", BCP 100, RFC 4020, February
          2005.

Informative References

RFC3567 Li, T. and R. Atkinson, "Intermediate System to

          Intermediate System (IS-IS) Cryptographic Authentication",
          RFC 3567, July 2003.

RFC4090 Pan, P., Swallow, G., and A. Atlas, "Fast Reroute

          Extensions to RSVP-TE for LSP Tunnels", RFC 4090, May
          2005.

Authors' Addresses

JP Vasseur Cisco Systems, Inc 1414 Massachusetts Avenue Boxborough, MA 01719 USA

EMail: [email protected]

Stefano Previdi Cisco Systems, Inc Via Del Serafico 200 Roma 00142 Italy

EMail: [email protected]

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