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IETF RFC 6233
IS-IS Registry Extension for Purges
Last modified on Tuesday, May 10th, 2011
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Internet Engineering Task Force (IETF) T. Li
Request for Comments: 6233 L. Ginsberg
Updates: 3563, 5304, 5310 Cisco Systems, Inc.
Category: Standards Track May 2011
ISSN: 2070-1721
IS-IS Registry Extension for Purges
 Abstract
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
http://www.rfc-editor.org/info/RFC 6233.
Copyright Notice
Copyright (c) 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
(http://trustee.ietf.org/license-info) 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.
Li & Ginsberg Standards Track PAGE 1 
RFC 6233 Registry Extension for Purges May 2011
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 7.3.16.4 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 [RFC 5304] [RFC 5310], 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 [RFC 2119].
2. Registry Changes
This document extends the current "IS-IS TLV Codepoints" registry,
defined in [RFC 3563], 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.
Li & Ginsberg Standards Track PAGE 2
RFC 6233 Registry Extension for Purges May 2011
3. Purges and Authentication
Previous documents on authentication [RFC 5304] [RFC 5310] 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 [RFC 6232]. 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.
Li & Ginsberg Standards Track PAGE 3
RFC 6233 Registry Extension for Purges May 2011
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.
[RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC 3563] 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.
[RFC 5304] Li, T. and R. Atkinson, "IS-IS Cryptographic
Authentication", RFC 5304, October 2008.
[RFC 5310] Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R.,
and M. Fanto, "IS-IS Generic Cryptographic
Authentication", RFC 5310, February 2009.
[RFC 6232] 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
USA
EMail: tony.li@tony.li
Les Ginsberg
Cisco Systems, Inc.
170 W. Tasman Dr.
San Jose, CA 95134
USA
EMail: ginsberg@cisco.com
Li & Ginsberg Standards Track PAGE 4
IS-IS Registry Extension for Purges
RFC TOTAL SIZE: 8435 bytes
PUBLICATION DATE: Tuesday, May 10th, 2011
LEGAL RIGHTS: The IETF Trust (see BCP 78)
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