Internet-Draft LSP Ping for SR PSID August 2024
Min, et al. Expires 13 February 2025 [Page]
Workgroup:
MPLS Working Group
Internet-Draft:
draft-ietf-mpls-spring-lsp-ping-path-sid-02
Published:
Intended Status:
Standards Track
Expires:
Authors:
X. Min
ZTE Corp.
S. Peng
ZTE Corp.
L. Gong
China Mobile
R. Gandhi
Cisco Systems, Inc.
C. Pignataro
North Carolina State University

Label Switched Path (LSP) Ping for Segment Routing (SR) Path Segment Identifier with MPLS Data Planes

Abstract

Path Segment is a type of Segment Routing (SR) segment, and a Path Segment Identifier (PSID) is used to identify an SR path. Path Segment can be used in an SR over MPLS (SR-MPLS) data plane. This document provides Target Forwarding Equivalence Class (FEC) Stack TLV and sub-TLV definitions for PSID.

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at https://datatracker.ietf.org/drafts/current/.

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This Internet-Draft will expire on 13 February 2025.

Table of Contents

1. Introduction

Path Segment is a type of Segment Routing (SR) segment, and a Path Segment Identifier (PSID) is used to identify an SR path. PSID in MPLS-based segment routing networks is defined in [RFC9545].

As specified in [RFC9545], PSID is a single label inserted by the ingress node of the SR path, and then processed by the egress node of the SR path. The PSID is placed within the MPLS label stack as a label immediately following the last label of the SR path. The egress node MUST pop the PSID.

This document provides Target Forwarding Equivalence Class (FEC) Stack TLV and sub-TLV definitions for PSID. Procedures for LSP Ping as defined in [RFC8287] and [RFC8690] are applicable to PSID as well. Note that LSP Traceroute is left out of this document because the transit node is not involved in PSID processing.

2. Conventions

2.1. 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.

2.2. Terminology

This document uses the terminology defined in [RFC3031], [RFC8402], and [RFC8029], readers are expected to be familiar with those terms.

3. Path Segment ID Sub-TLVs

Analogous to what's defined in Section 5 of [RFC8287] and Section 4 of [I-D.ietf-mpls-sr-epe-oam], three new sub-TLVs are defined for the Target FEC Stack TLV (Type 1), the Reverse-Path Target FEC Stack TLV (Type 16), and the Reply Path TLV (Type 21).

     Sub-Type    Sub-TLV Name
     --------    -----------------------------
      TBD1       SR Policy's PSID
      TBD2       SR Candidate Path's PSID
      TBD3       SR Segment List's PSID

As specified in Section 2 of [RFC9545], a PSID is used to identify a segment list, some or all segment lists in a Candidate path or an SR policy, so three different Target FEC Stack sub-TLVs need to be defined for PSID. When a PSID is used to identify an SR Policy, the Target FEC Stack sub-TLV of the type "SR Policy's PSID" would be used to validate the control plane to forwarding plane synchronization for this PSID; When a PSID is used to identify an SR Candidate Path, the Target FEC Stack sub-TLV of the type "SR Candidate Path's PSID" would be used to validate the control plane to forwarding plane synchronization for this PSID; When a PSID is used to identify a Segment List, the Target FEC Stack sub-TLV of the type "SR Segment List's PSID" would be used to validate the control plane to forwarding plane synchronization for this PSID. Note that the three new Target FEC Stack sub-TLVs are mutual exclusive and they wouldn't be present in one message simultaneously.

3.1. SR Policy's PSID

The format of SR Policy's PSID sub-TLV is specified 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 = TBD1          |             Length            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~                     Headend  (4/16 octets)                    ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                       Color  (4 octets)                       |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~                    Endpoint  (4/16 octets)                    ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: SR Policy's PSID sub-TLV

Type

Length

Headend

Color

Endpoint

3.2. SR Candidate Path's PSID

The format of SR Candidate Path's PSID sub-TLV is specified 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 = TBD2          |             Length            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~                     Headend  (4/16 octets)                    ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                       Color  (4 octets)                       |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~                    Endpoint  (4/16 octets)                    ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Protocol-Origin|                    Reserved                   |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                                                               |
|                                                               |
|                  Originator  (20 octets)                      |
|                                                               |
|                                                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|               Discriminator  (4 octets)                       |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: SR Candidate Path's PSID sub-TLV

Type

Length

Headend

Color

Endpoint

Protocol-Origin

Originator

Discriminator

3.3. SR Segment List's PSID

The format of SR Segment List's PSID sub-TLV is specified 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 = TBD3          |             Length            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~                     Headend  (4/16 octets)                    ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                       Color  (4 octets)                       |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~                    Endpoint  (4/16 octets)                    ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Protocol-Origin|                    Reserved                   |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                                                               |
|                                                               |
|                  Originator  (20 octets)                      |
|                                                               |
|                                                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|               Discriminator  (4 octets)                       |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|             Segment-List-ID  (4 octets)                       |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: SR Segment List's PSID sub-TLV

Type

Length

Headend

Color

Endpoint

Protocol-Origin

Originator

Discriminator

Segment-List-ID

4. PSID FEC Validation

The MPLS LSP Ping procedures may be initiated by the headend of the Segment Routing path or a centralized topology-aware data plane monitoring system as described in [RFC8403]. For the PSID, the responder nodes that receive echo request and send echo reply MUST be the endpoint of the Segment Routing path.

When an endpoint receives the LSP echo request packet with top FEC being the PSID, it MUST perform validity checks on the content of the PSID FEC Stack sub-TLV. The basic length check should be performed on the received FEC.

    SR Policy's PSID
    ------------------
    Length = 12 or 36 octets

    SR Candidate Path's PSID
    ------------------
    Length = 40 or 64 octets

    SR Segment List's PSID
    ------------------
    Length = 44 or 68 octets

If a malformed FEC Stack sub-TLV is received, then a return code of 1, "Malformed echo request received" as defined in [RFC8029] SHOULD be sent. The below section augments Section 7.4 of [RFC8287].

When a sub-TLV defined in this document is carried in Reverse-Path Target FEC Stack TLV (Type 16) or Reply Path TLV (Type 21), it MUST be sent by an endpoint in an echo reply. The headend MUST perform validity checks as described above without setting the return code. If any of the validations fail, then the headend MUST drop the echo reply and SHOULD log and/or report an error.

5. Security Considerations

This document defines additional MPLS LSP Ping sub-TLVs and follows the mechanisms defined in [RFC8029]. All the security considerations defined in [RFC8029] will be applicable for this document and, in addition, the MPLS LSP Ping sub-TLVs defined in this document do not impose any additional security challenges to be considered.

6. IANA Considerations

IANA is requested to assign three new sub-TLVs from the "Sub-TLVs for TLV Types 1, 16, and 21" sub-registry in the "TLVs" registry of the "Multiprotocol Label Switching (MPLS) Label Switched Paths (LSPs) Ping Parameters" name space. The Standards Action range that requires an error message to be returned if the sub-TLV is not recognized (range 0-16383) should be used.

  Sub-Type   Sub-TLV Name                    Reference
  --------   -----------------------------   ------------
   TBD1      SR Policy's PSID            Section 3.1
   TBD2      SR Candidate Path's PSID    Section 3.2
   TBD3      SR Segment List's PSID      Section 3.3

7. Acknowledgements

The authors would like to acknowledge Loa Andersson, Detao Zhao, Ben Niven-Jenkins, and Greg Mirsky for their thorough review and very helpful comments.

The authors would like to acknowledge Yao Liu for the very helpful f2f discussion.

8. References

8.1. Normative References

[RFC2119]
Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <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, , <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, , <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, , <https://www.rfc-editor.org/info/rfc8287>.
[RFC8690]
Nainar, N., Pignataro, C., Iqbal, F., and A. Vainshtein, "Clarification of Segment ID Sub-TLV Length for RFC 8287", RFC 8690, DOI 10.17487/RFC8690, , <https://www.rfc-editor.org/info/rfc8690>.
[RFC9256]
Filsfils, C., Talaulikar, K., Ed., Voyer, D., Bogdanov, A., and P. Mattes, "Segment Routing Policy Architecture", RFC 9256, DOI 10.17487/RFC9256, , <https://www.rfc-editor.org/info/rfc9256>.
[RFC9545]
Cheng, W., Ed., Li, H., Li, C., Ed., Gandhi, R., and R. Zigler, "Path Segment Identifier in MPLS-Based Segment Routing Networks", RFC 9545, DOI 10.17487/RFC9545, , <https://www.rfc-editor.org/info/rfc9545>.

8.2. Informative References

[I-D.ietf-idr-sr-policy-path-segment]
Li, C., Li, Z., Yin, Y., Cheng, W., and K. Talaulikar, "SR Policy Extensions for Path Segment and Bidirectional Path", Work in Progress, Internet-Draft, draft-ietf-idr-sr-policy-path-segment-11, , <https://datatracker.ietf.org/doc/html/draft-ietf-idr-sr-policy-path-segment-11>.
[I-D.ietf-idr-sr-policy-safi]
Previdi, S., Filsfils, C., Talaulikar, K., Mattes, P., and D. Jain, "Advertising Segment Routing Policies in BGP", Work in Progress, Internet-Draft, draft-ietf-idr-sr-policy-safi-06, , <https://datatracker.ietf.org/doc/html/draft-ietf-idr-sr-policy-safi-06>.
[I-D.ietf-idr-sr-policy-seglist-id]
Lin, C., Cheng, W., Liu, Y., Talaulikar, K., and M. Chen, "BGP SR Policy Extensions for Segment List Identifier", Work in Progress, Internet-Draft, draft-ietf-idr-sr-policy-seglist-id-01, , <https://datatracker.ietf.org/doc/html/draft-ietf-idr-sr-policy-seglist-id-01>.
[I-D.ietf-mpls-sr-epe-oam]
Hegde, S., Srivastava, M., Arora, K., Ninan, S., and X. Xu, "Label Switched Path (LSP) Ping/Traceroute for Segment Routing (SR) Egress Peer Engineering Segment Identifiers (SIDs) with MPLS Data Plane", Work in Progress, Internet-Draft, draft-ietf-mpls-sr-epe-oam-19, , <https://datatracker.ietf.org/doc/html/draft-ietf-mpls-sr-epe-oam-19>.
[I-D.ietf-pce-multipath]
Koldychev, M., Sivabalan, S., Saad, T., Beeram, V. P., Bidgoli, H., Yadav, B., Peng, S., and G. S. Mishra, "PCEP Extensions for Signaling Multipath Information", Work in Progress, Internet-Draft, draft-ietf-pce-multipath-11, , <https://datatracker.ietf.org/doc/html/draft-ietf-pce-multipath-11>.
[I-D.ietf-pce-segment-routing-policy-cp]
Koldychev, M., Sivabalan, S., Barth, C., Peng, S., and H. Bidgoli, "Path Computation Element Communication Protocol (PCEP) Extensions for Segment Routing (SR) Policy Candidate Paths", Work in Progress, Internet-Draft, draft-ietf-pce-segment-routing-policy-cp-17, , <https://datatracker.ietf.org/doc/html/draft-ietf-pce-segment-routing-policy-cp-17>.
[I-D.ietf-pce-sr-path-segment]
Li, C., Chen, M., Cheng, W., Gandhi, R., and Q. Xiong, "Path Computation Element Communication Protocol (PCEP) Extension for Path Segment in Segment Routing (SR)", Work in Progress, Internet-Draft, draft-ietf-pce-sr-path-segment-09, , <https://datatracker.ietf.org/doc/html/draft-ietf-pce-sr-path-segment-09>.
[RFC3031]
Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol Label Switching Architecture", RFC 3031, DOI 10.17487/RFC3031, , <https://www.rfc-editor.org/info/rfc3031>.
[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, , <https://www.rfc-editor.org/info/rfc8402>.
[RFC8403]
Geib, R., Ed., Filsfils, C., Pignataro, C., Ed., and N. Kumar, "A Scalable and Topology-Aware MPLS Data-Plane Monitoring System", RFC 8403, DOI 10.17487/RFC8403, , <https://www.rfc-editor.org/info/rfc8403>.

Authors' Addresses

Xiao Min
ZTE Corp.
Nanjing
China
Shaofu Peng
ZTE Corp.
Nanjing
China
Liyan Gong
China Mobile
Beijing
China
Rakesh Gandhi
Cisco Systems, Inc.
Canada
Carlos Pignataro
North Carolina State University
United States of America