Internet DRAFT - draft-zhou-spring-srh-le-change
draft-zhou-spring-srh-le-change
Network Working Group T. Zhou
Internet-Draft J. Xie
Updates: 8754 (if approved) Huawei Technologies
Intended status: Standards Track 10 March 2023
Expires: 11 September 2023
Define the Value 255 in Last Entry field of Segment Routing Header
draft-zhou-spring-srh-le-change-01
Abstract
This document proposes to define the value 255 in Last Entry field in
Segment Routing Header (SRH) [RFC8754], to indicate an SRH without
any SID left.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on 11 September 2023.
Copyright Notice
Copyright (c) 2023 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terms and Abbreviations . . . . . . . . . . . . . . . . . . . 2
3. The Problem and the Proposal . . . . . . . . . . . . . . . . 2
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 3
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 3
6. Normative References . . . . . . . . . . . . . . . . . . . . 3
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 3
1. Introduction
This document proposes to define the value 255 in Last Entry field in
Segment Routing Header (SRH) [RFC8754], to indicate an SRH without
any SID present.
2. Terms and Abbreviations
The following abbreviations are used in this document.
* SRH: Segment Routing Header
* LE: Last Entry
* SL: Segment Left
3. The Problem and the Proposal
Segment Routing Header (SRH) [RFC8754] is one type of Routing Header
(RH) [RFC8200]. A Segment Left field is defined in [RFC8200] as the
basic structure of any type of RH. A Last Entry field is defined in
[RFC8754] as the structure of SRH. The two fields are both related
to the segments, behaving as pointer to one of the segments in the
SRH. When the Segment Left field is set to one and the Last Entry
field is set to zero, there is one SID present in the SRH. However,
with current specification [RFC8754], there is no way to indicate an
SRH without any SID present. For example, there is no need for any
segment in the Segment List of SRH (the so-called SRv6-BE case), but
there is need for HMAC in SRH as the enhanced security mechanism.
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This document proposes to use the value 255 of Last Entry field to
represent that there is no SID in the Segment List part of the SRH.
Accordingly, the Segment Left field MUST be zero in this case.
This has an impact that, the number of Segments allowed in an SRH
shrinks, from maximum 256 to maximum 255. Practically this is not a
big problem, because the number of segments bigger than 255 is very
impossible. Thus, changing the meaning of Last Entry value 255 can
support incremental development and deployment.
4. IANA Considerations
There is no relevant IANA codepoint
5. Acknowledgements
TBD.
6. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", STD 86, RFC 8200,
DOI 10.17487/RFC8200, July 2017,
<https://www.rfc-editor.org/info/rfc8200>.
[RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J.,
Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
(SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020,
<https://www.rfc-editor.org/info/rfc8754>.
Authors' Addresses
Tianran Zhou
Huawei Technologies
Email: zhoutianran@huawei.com
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Jingrong Xie
Huawei Technologies
Email: xiejingrong@huawei.com
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