Updates to the IS-IS TLV Codepoints Registry
Tidies two IS-IS sub-TLV registries and tells Designated Experts when they may allocate codepoints early.
Ginsberg, L., "Updates to the IS-IS TLV Codepoints Registry", RFC 7370, DOI 10.17487/RFC7370, September 2014, <https://www.rfc-editor.org/info/rfc7370>.
@misc{rfc7370,
series = {Request for Comments},
number = 7370,
howpublished = {RFC 7370},
publisher = {RFC Editor},
doi = {10.17487/RFC7370},
url = {https://www.rfc-editor.org/info/rfc7370},
author = {L. Ginsberg},
title = {{Updates to the IS-IS TLV Codepoints Registry}},
pagetotal = 7,
year = 2014,
month = sep,
} RFC text
Contents
Internet Engineering Task Force (IETF) L. Ginsberg
Request for Comments: 7370 Cisco Systems
Category: Standards Track September 2014
ISSN: 2070-1721
Updates to the IS-IS TLV Codepoints Registry
Abstract
This document recommends some editorial changes to the IANA "IS-IS
TLV Codepoints" registry to more accurately document the state of the
protocol. It also sets out new guidelines for Designated Experts to
apply when reviewing allocations from the registry.
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/rfc7370.
Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. IS Neighbor Sub-TLV Registry . . . . . . . . . . . . . . . . 4
3. Prefix Reachability Sub-TLV Registry . . . . . . . . . . . . 4
4. Guidance for Designated Experts . . . . . . . . . . . . . . . 4
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . 5
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
7.1. Normative References . . . . . . . . . . . . . . . . . . 6
7.2. Informative References . . . . . . . . . . . . . . . . . 6
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 7
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
The "IS-IS TLV Codepoints" registry was created by [RFC3563] and
extended by [RFC6233]. The assignment policy for the registry is
"Expert Review" as defined in [RFC5226]. As documents related to
IS-IS are developed, the codepoints required for the protocol
extensions are reviewed by the Designated Experts and added to the
IANA-managed registry. As these documents are published as RFCs, the
registries are updated to reference the relevant RFC.
In the case of TLVs supporting prefix advertisement, currently
separate sub-TLV registries are maintained for each TLV. These
registries need to be combined into a common sub-TLV registry similar
to what has been done for neighbor advertisement TLVs.
In some cases, there is a need to allocate codepoints defined in
Internet-Drafts (I-Ds) that seem likely to eventually gain Working
Group approval, without waiting for those I-Ds to be published as
RFCs. This can be achieved using Expert Review, and this document
sets out guidance for the Designated Experts to apply when reviewing
allocations from the registry.
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 [RFC2119].
2. IS Neighbor Sub-TLV Registry
There was an existing common sub-TLV registry named "Sub-TLVs for
TLVs 22, 141, and 222". [RFC5311] defines the IS Neighbor Attribute
TLV (23) and the MT IS Neighbor Attribute TLV (223). The format of
these TLVs is identical to TLVs 22 and 222, respectively. The IS
Neighbor sub-TLV registry has been extended to include these two
TLVs. Settings for inclusion of each sub-TLV are identical to the
settings for TLVs 22 and 222, respectively.
3. Prefix Reachability Sub-TLV Registry
Previously, there existed separate sub-TLV registries for TLVs 135,
235, 236, and 237. As in the case of the IS Neighbor TLVs discussed
in the previous section, assignment of sub-TLVs applicable to one or
more of these TLVs is intended to be common. Therefore, the existing
separate sub-TLV registries have been combined into a single registry
entitled "Sub-TLVs for TLVs 135, 235, 236, and 237". As existing
sub-TLV assignments are common to all the TLVs, this represents no
change to the protocol -- only a clearer representation of the
intended sub-TLV allocation strategy. The format of the registry is
as shown below:
Type Description 135 235 236 237 Reference
---- ------------ --- --- --- --- ---------
0 Unassigned
1 32-bit Administrative Tag Sub-TLV y y y y [RFC5130]
2 64-bit Administrative Tag Sub-TLV y y y y [RFC5130]
3-255 Unassigned
4. Guidance for Designated Experts
When new I-Ds are introduced requiring new codepoints, it is
advantageous to be able to allocate codepoints without waiting for
them to progress to RFC. The reasons this is advantageous are
described in [RFC7120]. However, the procedures in [RFC7120] for
early allocation do not apply to registries, such as the "IS-IS TLV
Codepoints" registry, that utilize the "Expert Review" allocation
policy. In such cases, what is required is that a request be made to
the Designated Experts who MAY approve the assignments according to
the guidance that has been established for the registry concerned.
The following guidance applies specifically to the "IS-IS TLV
Codepoints" registry.
1. Application for a codepoint allocation MAY be made to the
Designated Experts at any time.
2. The Designated Experts SHOULD only consider requests that arise
from I-Ds that have already been accepted as Working Group
documents or that are planned for progression as AD Sponsored
documents in the absence of a suitably chartered Working Group.
3. In the case of Working Group documents, the Designated Experts
SHOULD check with the Working Group chairs that there is
consensus within the Working Group to make the allocation at this
time. In the case of AD Sponsored documents, the Designated
Experts SHOULD check with the AD for approval to make the
allocation at this time.
4. The Designated Experts SHOULD then review the assignment requests
on their technical merit. The Designated Experts SHOULD NOT seek
to overrule IETF consensus, but they MAY raise issues for further
consideration before the assignments are made.
5. Once the Designated Experts have granted approval, IANA will
update the registry by marking the allocated codepoints with a
reference to the associated document as normal.
6. In the event that the document fails to progress to RFC, the
Expiry and deallocation process defined in [RFC7120] MUST be
followed for the relevant codepoints -- noting that the
Designated Experts perform the role assigned to Working Group
chairs.
5. IANA Considerations
This document provides guidance to the Designated Experts appointed
to manage allocation requests in the "IS-IS TLV Codepoints" registry.
IANA has updated the registry that was specified as "Sub-TLVs for
TLVs 22, 141, and 222" to be named "Sub-TLVs for TLVs 22, 23, 141,
222, and 223".
Per this document, the existing sub-TLV registries for TLVs 135, 235,
236, and 237 have been combined into a single registry -- the
"Sub-TLVs for TLVs 135, 235, 236, and 237" registry -- as described
in Section 3.
6. Security Considerations
This document introduces no new security issues.
7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC5130] Previdi, S., Shand, M., and C. Martin, "A Policy Control
Mechanism in IS-IS Using Administrative Tags", RFC 5130,
February 2008, <http://www.rfc-editor.org/info/rfc5130>.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008, <http://www.rfc-editor.org/info/rfc5226>.
[RFC5311] McPherson, D., Ginsberg, L., Previdi, S., and M. Shand,
"Simplified Extension of Link State PDU (LSP) Space for
IS-IS", RFC 5311, February 2009,
<http://www.rfc-editor.org/info/rfc5311>.
[RFC6233] Li, T. and L. Ginsberg, "IS-IS Registry Extension for
Purges", RFC 6233, May 2011,
<http://www.rfc-editor.org/info/rfc6233>.
[RFC7120] Cotton, M., "Early IANA Allocation of Standards Track Code
Points", BCP 100, RFC 7120, January 2014,
<http://www.rfc-editor.org/info/rfc7120>.
7.2. Informative References
[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, <http://www.rfc-editor.org/info/rfc3563>.
Acknowledgements
The author wishes to thank Alia Atlas and Amanda Baber for their
input in defining the correct process to follow to get these changes
implemented. Special thanks to Adrian Farrel for crafting the text
in Section 4.
Author's Address
Les Ginsberg
Cisco Systems
510 McCarthy Blvd.
Milpitas, CA 95035
United States
EMail: ginsberg@cisco.com
AI ELI5
On this page
§1Why the Registry Needed Changes
The IS-IS TLV Codepoints registry was created by RFC 3563 and extended by RFC 6233. Its assignment policy is Expert Review, as defined in RFC 5226: Designated Experts review the codepoints a protocol extension needs before IANA adds them.
Two problems motivated this document. Prefix advertisement TLVs each had their own separate sub-TLV registry, which should be combined as was already done for neighbor advertisement TLVs. And sometimes codepoints from Internet-Drafts that seem likely to gain Working Group approval are needed before those drafts become RFCs.
The list of numbered fields had grown messy, and reviewers had no clear rules for approving a new field early. This RFC fixes both.
§2The Two Sub-TLV Registries
An existing common registry named "Sub-TLVs for TLVs 22, 141, and 222" covered IS neighbor TLVs. RFC 5311 defines the IS Neighbor Attribute TLV (23) and the MT IS Neighbor Attribute TLV (223), whose formats are identical to TLVs 22 and 222. The registry was extended to include them, with identical inclusion settings, and renamed "Sub-TLVs for TLVs 22, 23, 141, 222, and 223".
For prefix reachability, separate sub-TLV registries previously existed for TLVs 135, 235, 236 and 237. Because sub-TLV assignments were already common to all of them, they were combined into one registry, "Sub-TLVs for TLVs 135, 235, 236, and 237". The RFC stresses this is no change to the protocol, only a clearer representation. The registry currently lists type 1 (32-bit Administrative Tag Sub-TLV) and type 2 (64-bit Administrative Tag Sub-TLV), both from RFC 5130 and valid for all four TLVs. Type 0 and types 3 to 255 are unassigned.
Several lists that always said the same thing were joined into one list, so nobody has to check four places any more.
- 0Unassigned — Not allocated.
- 132-bit Administrative Tag Sub-TLV — Applies to all four TLVs; RFC 5130.
- 264-bit Administrative Tag Sub-TLV — Applies to all four TLVs; RFC 5130.
- 3-255Unassigned — Not allocated.
§4Guidance for Designated Experts
Early allocation under RFC 7120 does not apply to Expert Review registries. Instead, a request goes to the Designated Experts, who MAY approve it under the registry's guidance. Six rules apply to the IS-IS TLV Codepoints registry.
- Requests MAY be made at any time.
- Experts SHOULD only consider requests from drafts already accepted as Working Group documents, or planned as AD Sponsored documents when no suitable Working Group exists.
- For Working Group documents, experts SHOULD check with the chairs that there is consensus to allocate now. For AD Sponsored documents, they SHOULD check with the AD.
- Experts SHOULD review the technical merit. They SHOULD NOT overrule IETF consensus but MAY raise issues first.
- After approval, IANA marks the codepoints with a reference to the document as normal.
- If the document never becomes an RFC, the expiry and deallocation process of RFC 7120 MUST be followed, with the Designated Experts taking the role of the Working Group chairs.
Reviewers may say yes early, but only to ideas that a real team has already accepted. If the idea is dropped, they take the number back.
§5IANA Actions and Security
IANA has renamed the neighbor sub-TLV registry to "Sub-TLVs for TLVs 22, 23, 141, 222, and 223" and combined the prefix sub-TLV registries for TLVs 135, 235, 236 and 237 into one. The document otherwise provides guidance to the Designated Experts who manage allocation requests.
IANA, the keeper of the lists, made the name changes and joined the lists.
§6Security Considerations
The Security Considerations section is a single sentence: the document introduces no new security issues. That fits its scope, since it renames and merges registries and sets review guidance without changing any IS-IS message format.
Nothing here makes anything less safe, because only the lists were tidied.
§7What Changes in Practice
For implementers, nothing on the wire changes: existing sub-TLV assignments were already common to all the TLVs sharing a registry. For people writing new IS-IS extensions, the practical change is the path in Section 4. A draft backed by a Working Group, or planned as AD Sponsored, can get codepoints from the Designated Experts without waiting to be published as an RFC.
The numbered fields stay the same. The only new thing is a faster, fair way to get a new number.