RFC8690: Clarification of Segment ID Sub-TLV Length for RFC 8287
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(mpls)
Internet Engineering Task Force (IETF) N. Nainar
Request for Comments: 8690 C. Pignataro
Updates: 8287 Cisco Systems, Inc.
Category: Standards Track F. Iqbal
ISSN: 2070-1721 Individual
A. Vainshtein
ECI Telecom
December 2019
Clarification of Segment ID Sub-TLV Length for RFC 8287
Abstract
RFC 8287 defines the extensions to perform LSP Ping and Traceroute
for Segment Routing IGP-Prefix and IGP-Adjacency Segment Identifiers
(SIDs) with the MPLS data plane. RFC 8287 proposes three Target
Forwarding Equivalence Class (FEC) Stack sub-TLVs. While RFC 8287
defines the format and procedure to handle those sub-TLVs, it does
not sufficiently clarify how the length of the Segment ID sub-TLVs
should be computed to be included in the Length field of the sub-
TLVs. This ambiguity has resulted in interoperability issues.
This document updates RFC 8287 by clarifying the length of each of
the Segment ID sub-TLVs defined in RFC 8287.
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 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc8690.
Copyright Notice
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Table of Contents
1. Introduction
2. Terminology
3. Requirements Notation
4. Length Field Clarification for Segment ID Sub-TLVs
4.1. IPv4 IGP-Prefix Segment ID Sub-TLV
4.2. IPv6 IGP-Prefix Segment ID Sub-TLV
4.3. IGP-Adjacency Segment ID Sub-TLV
5. IANA Considerations
6. Security Considerations
7. Normative References
Acknowledgements
Contributors
Authors' Addresses
1. Introduction
[RFC8287] defines the extensions to MPLS LSP Ping and Traceroute for
Segment Routing IGP-Prefix and IGP-Adjacency Segment Identifiers
(SIDs) with the MPLS data plane. [RFC8287] proposes three Target FEC
Stack sub-TLVs. While RFC 8287 defines the format and procedure to
handle those sub-TLVs, it does not sufficiently clarify how the
length of the Segment ID sub-TLVs should be computed to be included
in the Length field of the sub-TLVs, which may result in
interoperability issues.
This document updates [RFC8287] by clarifying the length of each
Segment ID sub-TLVs defined in [RFC8287].
2. Terminology
This document uses the terminology defined in [RFC8402], [RFC8029],
and [RFC8287]; readers are expected to be familiar with the terms as
used in those documents.
3. Requirements Notation
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.
4. Length Field Clarification for Segment ID Sub-TLVs
Section 5 of [RFC8287] defines three different Segment ID sub-TLVs
that can be included in the Target FEC Stack TLV defined in
[RFC8029]. The length of each sub-TLV MUST be calculated as defined
in this section.
The TLV representations defined in Sections 5.1, 5.2, and 5.3 of
[RFC8287] are updated to clarify the length calculations, as shown in
Sections 4.1, 4.2, and 4.3, respectively. The updated TLV
representations contain explicitly defined lengths.
4.1. IPv4 IGP-Prefix Segment ID Sub-TLV
The sub-TLV length for the IPv4 IGP-Prefix Segment ID MUST be set to
8, as shown in the TLV format below:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Type = 34 (IPv4 IGP-Prefix SID)| Length = 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 prefix |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Prefix Length | Protocol | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
4.2. IPv6 IGP-Prefix Segment ID Sub-TLV
The sub-TLV length for the IPv6 IGP-Prefix Segment ID MUST be set to
20, as shown in the TLV format below:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Type = 35 (IPv6 IGP-Prefix SID)| Length = 20 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| |
| IPv6 Prefix |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Prefix Length | Protocol | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
4.3. IGP-Adjacency Segment ID Sub-TLV
The sub-TLV length for the IGP-Adjacency Segment ID varies depending
on the Adjacency Type and Protocol. In any of the allowed
combinations of Adjacency Type and Protocol, the sub-TLV length MUST
be calculated by including 2 octets of the Reserved field. Table 1
lists the length for different combinations of Adj. Type and
Protocol.
+----------+-------------------------------------+
| Protocol | Length for Adj. Type |
| +----------+------+------+------------+
| | Parallel | IPv4 | IPv6 | Unnumbered |
+==========+==========+======+======+============+
| OSPF | 20 | 20 | 44 | 20 |
+----------+----------+------+------+------------+
| ISIS | 24 | 24 | 48 | 24 |
+----------+----------+------+------+------------+
| Any | 20 | 20 | 44 | 20 |
+----------+----------+------+------+------------+
Table 1: IGP-Adjacency SID Length Computation
For example, when the Adj. Type is set to Parallel Adjacency and the
Protocol is set to 0, the sub-TLV will be as below:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Type = 36 (IGP-Adjacency SID) | Length = 20 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Adj. Type = 1 | Protocol = 0 | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Local Interface ID (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remote Interface ID (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertising Node Identifier (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Receiving Node Identifier (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
5. IANA Considerations
IANA has listed this document as an additional reference for the
following entries in the "Sub-TLVs for TLV Types 1, 16, and 21"
registry:
+----------+----------------------------+---------------------+
| Sub-Type | Sub-TLV Name | Reference |
+==========+============================+=====================+
| 34 | IPv4 IGP-Prefix Segment ID | Section 5.1 of |
| | | [RFC8287]; RFC 8690 |
+----------+----------------------------+---------------------+
| 35 | IPv6 IGP-Prefix Segment ID | Section 5.2 of |
| | | [RFC8287]; RFC 8690 |
+----------+----------------------------+---------------------+
| 36 | IGP-Adjacency Segment ID | Section 5.3 of |
| | | [RFC8287]; RFC 8690 |
+----------+----------------------------+---------------------+
Table 2: Sub-TLVs for TLV Types 1, 16, and 21 (Updated Entries)
6. Security Considerations
This document updates [RFC8287] and does not introduce any additional
security considerations.
7. 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>.
[RFC8029] Kompella, K., Swallow, G., Pignataro, C., Ed., Kumar, N.,
Aldrin, S., and M. Chen, "Detecting Multiprotocol Label
Switched (MPLS) Data-Plane Failures", RFC 8029,
DOI 10.17487/RFC8029, March 2017,
<https://www.rfc-editor.org/info/rfc8029>.
[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>.
[RFC8287] Kumar, N., Ed., Pignataro, C., Ed., Swallow, G., Akiya,
N., Kini, S., and M. Chen, "Label Switched Path (LSP)
Ping/Traceroute for Segment Routing (SR) IGP-Prefix and
IGP-Adjacency Segment Identifiers (SIDs) with MPLS Data
Planes", RFC 8287, DOI 10.17487/RFC8287, December 2017,
<https://www.rfc-editor.org/info/rfc8287>.
[RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
July 2018, <https://www.rfc-editor.org/info/rfc8402>.
Acknowledgements
The authors would like to thank Michael Gorokhovsky and Manohar
Doppalapudi for investigating the interoperability issue during
European Advanced Network Test Center (EANTC) testing.
Contributors
The following individual contributed to this document: Zafar Ali,
Cisco Systems, Inc.
Authors' Addresses
Nagendra Kumar Nainar
Cisco Systems, Inc.
7200-12 Kit Creek Road
Research Triangle Park, NC 27709
United States of America
Email: naikumar@cisco.com
Carlos Pignataro
Cisco Systems, Inc.
7200-11 Kit Creek Road
Research Triangle Park, NC 27709
United States of America
Email: cpignata@cisco.com
Faisal Iqbal
Individual
Canada
Email: faisal.ietf@gmail.com
Alexander Vainshtein
ECI Telecom
Israel
Email: vainshtein.alex@gmail.com