Definition of an IS-IS Link Attribute Sub-TLV
Author(s): JP. Vasseur, S. Previdi
This document defines a sub-TLV called 'Link-attributes' carried within the TLV 22 and used to flood some link characteristics. [STANDARDS...
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. Table of Contents 1. Introduction ....................................................2 1.1. Terminology ................................................2 2. Link-Attributes Sub-TLV Format ..................................2 3. Interoperability with Routers Not Supporting This Capability ....3 4. IANA Considerations .............................................3 5. Security Considerations .........................................3 6. Acknowledgements ................................................3 7. References ......................................................4 7.1. Normative References .......................................4 7.2. Informative References .....................................4 Vasseur & Previdi Standards Track [Page 1] RFC 5029 IS-IS Link Attribute September 2007 1. Introduction [IS-IS] specifies the IS-IS protocol (ISO 10589) with extensions to support IPv4 in [RFC 1195]. A router advertises one or several Link State Protocol data units that are composed of variable length tuples called TLVs (Type-Length-Value). [RFC 3784] 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 [RFC 3784]. 1.1 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 [RFC 2119]. 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 ([RFC 3784]): 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., [RFC 4090]). 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. Vasseur & Previdi Standards Track [Page 2] RFC 5029 IS-IS Link Attribute September 2007 3. Interoperability with Routers Not Supporting This Capability A router not supporting the link-attribute sub-TLV will just silently ignore this sub-TLV. 4. 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 [RFC 2434], with Early Allocation (defined in [RFC4020]) permitted. 5. 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 [RFC 3567], should be applied if there is high risk resulting from the modification of capability information. 6. Acknowledgements The authors would like to thank Mike Shand, Les Ginsberg, and Bill Fenner for their useful comments. Vasseur & Previdi Standards Track [Page 3] RFC 5029 IS-IS Link Attribute September 2007 7. References 7.1. 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. [RFC 1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and dual environments", RFC 1195, December 1990. [RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC 2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 2434, October 1998. [RFC 3784] 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, RFC4020, February 2005. 7.2. Informative References [RFC 3567] Li, T. and R. Atkinson, "Intermediate System to Intermediate System (IS-IS) Cryptographic Authentication", RFC 3567, July 2003. [RFC 4090] Pan, P., Swallow, G., and A. Atlas, "Fast Reroute Extensions to RSVP-TE for LSP Tunnels", RFC 4090, May 2005. Vasseur & Previdi Standards Track [Page 4] RFC 5029 IS-IS Link Attribute September 2007 Authors' Addresses JP Vasseur Cisco Systems, Inc 1414 Massachusetts Avenue Boxborough, MA 01719 USA EMail: firstname.lastname@example.org Stefano Previdi Cisco Systems, Inc Via Del Serafico 200 Roma 00142 Italy EMail: email@example.com Vasseur & Previdi Standards Track [Page 5] RFC 5029 IS-IS Link Attribute September 2007 Full Copyright Statement Copyright (C) The IETF Trust (2007). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. 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