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rfc: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.

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 [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 in RFC 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 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 [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 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.
 [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 2007

Authors' 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.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.
 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.

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Vasseur & Previdi Standards Track [Page 6]

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