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Network Working Group                                        JP. VasseurRequest for Comments: 5029                                    S. PrevidiCategory: Standards Track                             Cisco Systems, Inc                                                          September 2007Definition of an IS-IS Link Attribute Sub-TLVStatus 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 Contents1. Introduction ....................................................21.1. Terminology ................................................22. Link-Attributes Sub-TLV Format ..................................23. Interoperability with Routers Not Supporting This Capability ....34. IANA Considerations .............................................35. Security Considerations .........................................36. Acknowledgements ................................................37. References ......................................................47.1. Normative References .......................................47.2. Informative References .....................................4Vasseur & Previdi           Standards Track                     [Page 1]

RFC 5029                  IS-IS Link Attribute            September 20071.  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].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 inRFC 2119 [RFC2119].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 ([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.Vasseur & Previdi           Standards Track                     [Page 2]

RFC 5029                  IS-IS Link Attribute            September 20073.  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 [RFC2434], 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 [RFC3567], 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 20077.  References7.1.  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.   [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              2005.7.2.  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.Vasseur & Previdi           Standards Track                     [Page 4]

RFC 5029                  IS-IS Link Attribute            September 2007Authors' Addresses   JP Vasseur   Cisco Systems, Inc   1414 Massachusetts Avenue   Boxborough, MA  01719   USA   EMail: jpv@cisco.com   Stefano Previdi   Cisco Systems, Inc   Via Del Serafico 200   Roma  00142   Italy   EMail: sprevidi@cisco.comVasseur & Previdi           Standards Track                     [Page 5]

RFC 5029                  IS-IS Link Attribute            September 2007Full Copyright Statement   Copyright (C) The IETF Trust (2007).   This document is subject to the rights, licenses and restrictions   contained inBCP 78, and except as set forth therein, the authors   retain all their rights.   This document and the information contained herein are provided on an   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND   THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS   OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF   THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.Intellectual Property   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 inBCP 78 andBCP 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 athttp://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.Vasseur & Previdi           Standards Track                     [Page 6]