| RFC 8690 | Clarification of Segment ID Sub-TLV Length for RFC 8287 | December 2019 |
| Nainar, et al. | Standards Track | [Page] |
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.¶
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 (c) 2019 IETF Trust and the persons identified as the document authors. All rights reserved.¶
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[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].¶
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.¶
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.¶
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.¶
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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+¶
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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+¶
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 |
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) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+¶
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], This document |
| 35 | IPv6 IGP-Prefix Segment ID | Section 5.2 of [RFC8287], This document |
| 36 | IGP-Adjacency Segment ID | Section 5.3 of [RFC8287], This document |
This document updates [RFC8287] and does not introduce any additional security considerations.¶
The authors would like to thank Michael Gorokhovsky and Manohar Doppalapudi for investigating the interoperability issue during European Advanced Network Test Center (EANTC) testing.¶
The following individual contributed to this document: Zafar Ali, Cisco Systems, Inc.¶