Internet Engineering Task Force (IETF)
Request for Comments: 6233
Updates: 3563, 5304, 5310
Category: Standards Track
ISSN: 2070-1721
T. Li
L. Ginsberg
Cisco Systems, Inc.
May 2011

IS-IS Registry Extension for Purges


IANA maintains the "IS-IS TLV Codepoints" registry. This registry documents which TLVs can appear in different types of IS-IS Protocol Data Units (PDUs), but does not document which TLVs can be found in zero Remaining Lifetime Link State PDUs (LSPs), a.k.a. purges. This document extends the existing registry to record the set of TLVs that are permissible in purges and updates the rules for generating and processing purges in the presence of authentication. This document updates RFC 3563, RFC 5304, and RFC 5310.

Status of This Memo

This is an Internet Standards Track document.

This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 5741.

Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at

Copyright Notice

Copyright © 2011 IETF Trust and the persons identified as the document authors. All rights reserved.

This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents ( in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.

Table of Contents

   1. Introduction ....................................................2
      1.1. Requirements Language ......................................2
   2. Registry Changes ................................................2
   3. Purges and Authentication .......................................3
   4. IANA Considerations .............................................3
   5. Security Considerations .........................................3
   6. Normative References ............................................4

1. Introduction

The IS-IS [ISO-10589] routing protocol maintains a link state database of the topology of its routing domain by flooding a set of Link State Protocol Data Units (LSPs). When the protocol no longer needs the information stored in an LSP, it uses the purge mechanism to cause the Intermediate Systems (ISs) in its domain to discard the information contained in the LSP. The process for generating purges can be found in Section of [ISO-10589]. This process retains only the LSP header, discarding any TLVs that had been carried within the LSP.

Subsequent enhancements to IS-IS, such as [RFC5304] [RFC5310], amend the process of generating a purge and allow the inclusion of certain TLVs in purges.

1.1. Requirements Language

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 [RFC2119].

2. Registry Changes

This document extends the current "IS-IS TLV Codepoints" registry, defined in [RFC3563], to record the set of TLVs that MAY be found in purges. All other TLVs MUST NOT appear in purges. This will serve as an aid to subsequent documents, which can then refer to the registry as the definitive list of the TLVs allowed in purges. This will also act as an aid to implementers, providing them with an easily accessible compendium of allowable TLVs.

The purge status defined for a given TLV applies to all sub-TLVs defined for that TLV.

3. Purges and Authentication

Previous documents on authentication [RFC5304] [RFC5310] required that an IS only accept a purge if it only contained the Authentication TLV.

This document updates and generalizes that behavior as follows: an implementation that implements authentication MUST NOT accept a purge that contains any TLV listed in the registry that is not acceptable in a purge. An implementation MUST NOT accept a purge that contains a TLV not listed in the registry unless the purge also contains the Purge Originator Identification (POI) TLV [RFC6232]. Purges that are accepted MUST be propagated without removal of TLVs. If multiple purges are received for the same LSP, then the implementation MAY propagate any one of the purges.

If an implementation that implements authentication accepts a purge that does not include the POI TLV and it chooses to insert the POI TLV, it MUST also recompute authentication.

ISs MUST NOT accept LSPs with a non-zero Remaining Lifetime that contain the POI TLV.

Purge generation is updated as follows: an implementation that implements authentication generates a purge by first removing any TLVs that are not listed in the registry as being acceptable in purges. The POI TLV MUST be added. Then any other TLVs that MAY be in purges, as shown by the registry, MAY be added. Finally, authentication, if any, is added.

4. IANA Considerations

IANA has modified the "IS-IS TLV Codepoints" registry by adding a column in the registry for 'Purge'. A 'y' in this column indicates that the TLV for this row MAY be found in a purge. An 'n' in this column indicates that the TLV for this row MUST NOT be found in a purge.

The 'Purge' column should initially contain a 'y' for TLV type 10 (Authentication) and for TLV type 137 (Dynamic hostname). All other entries in this column should have an 'n'. Other additions to this registry should explicitly specify their value for this column.

5. Security Considerations

This document introduces no new security issues.

6. Normative References

   [ISO-10589]  ISO, "Intermediate system to Intermediate system
                intra-domain routeing information exchange protocol for
                use in conjunction with the protocol for providing the
                connectionless-mode Network Service (ISO 8473)",
                ISO/IEC 10589:2002.
   [RFC2119]    Bradner, S., "Key words for use in RFCs to Indicate
                Requirement Levels", BCP 14, RFC 2119, March 1997.
   [RFC3563]    Zinin, A., "Cooperative Agreement Between the ISOC/IETF
                and ISO/IEC Joint Technical Committee 1/Sub Committee 6
                (JTC1/SC6) on IS-IS Routing Protocol Development",
                RFC 3563, July 2003.
   [RFC5304]    Li, T. and R. Atkinson, "IS-IS Cryptographic
                Authentication", RFC 5304, October 2008.
   [RFC5310]    Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R.,
                and M. Fanto, "IS-IS Generic Cryptographic
                Authentication", RFC 5310, February 2009.
   [RFC6232]    Wei, F., Qin, Y., Li, Z., Li, T., and J. Dong, "Purge
                Originator Identification TLV for IS-IS", RFC 6232,
                May 2011.

Authors' Addresses

   Tony Li
   Cisco Systems, Inc.
   170 W. Tasman Dr.
   San Jose, CA  95134
   Les Ginsberg
   Cisco Systems, Inc.
   170 W. Tasman Dr.
   San Jose, CA  95134