Label Switched Path Ping for Segment Routing Path Segment Identifier with MPLS Data Plane
draft-ietf-mpls-spring-lsp-ping-path-sid-13
| Document | Type | Active Internet-Draft (mpls WG) | |
|---|---|---|---|
| Authors | Xiao Min , Shaofu Peng , Liyan Gong , Rakesh Gandhi , Carlos Pignataro | ||
| Last updated | 2025-06-20 (Latest revision 2025-06-06) | ||
| Replaces | draft-xp-mpls-spring-lsp-ping-path-sid | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | Proposed Standard | ||
| Formats | |||
| Reviews | |||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | Submitted to IESG for Publication | |
| Document shepherd | Tarek Saad | ||
| Shepherd write-up | Show Last changed 2025-03-04 | ||
| IESG | IESG state | RFC Ed Queue | |
| Action Holders |
(None)
|
||
| Consensus boilerplate | Yes | ||
| Telechat date | (None) | ||
| Responsible AD | Jim Guichard | ||
| Send notices to | tsaad@cisco.com | ||
| IANA | IANA review state | Version Changed - Review Needed | |
| IANA action state | RFC-Ed-Ack | ||
| RFC Editor | RFC Editor state | EDIT | |
| Details |
draft-ietf-mpls-spring-lsp-ping-path-sid-13
MPLS Working Group X. Min
Internet-Draft S. Peng
Intended status: Standards Track ZTE Corp.
Expires: 8 December 2025 L. Gong
China Mobile
R. Gandhi
Cisco Systems, Inc.
C. Pignataro
Blue Fern Consulting
6 June 2025
Label Switched Path Ping for Segment Routing Path Segment Identifier
with MPLS Data Plane
draft-ietf-mpls-spring-lsp-ping-path-sid-13
Abstract
Segment Routing (SR) leverages source routing to steer packets
through an ordered list of instructions, called segments. SR can be
instantiated over the MPLS data plane. Path Segment Identifiers
(PSIDs) are used to identify and correlate bidirectional or end-to-
end paths in Segment Routing networks. This document defines
procedures (i.e. six new Target forwarding Equivalence Class (FEC)
Stack sub-TLVs) for the use of LSP Ping to support connectivity
verification and fault isolation for SR paths that include Path
Segment Identifiers. The mechanisms described enable the validation
and tracing of SR paths with Path SIDs in MPLS networks,
complementing existing SR-MPLS OAM capabilities.
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/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 8 December 2025.
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Copyright Notice
Copyright (c) 2025 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
extracted from this document must include Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
3. Path Segment ID Sub-TLVs . . . . . . . . . . . . . . . . . . 4
3.1. SR Policy Associated PSID - IPv4 Sub-TLV . . . . . . . . 5
3.2. SR Candidate Path Associated PSID - IPv4 Sub-TLV . . . . 6
3.3. SR Segment List Associated PSID - IPv4 Sub-TLV . . . . . 8
3.4. SR Policy Associated PSID - IPv6 Sub-TLV . . . . . . . . 10
3.5. SR Candidate Path Associated PSID - IPv6 Sub-TLV . . . . 11
3.6. SR Segment List Associated PSID - IPv6 Sub-TLV . . . . . 13
4. PSID FEC Validation . . . . . . . . . . . . . . . . . . . . . 15
4.1. PSID FEC Validation Rules . . . . . . . . . . . . . . . . 15
5. Security Considerations . . . . . . . . . . . . . . . . . . . 19
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 20
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 20
8.1. Normative References . . . . . . . . . . . . . . . . . . 20
8.2. Informative References . . . . . . . . . . . . . . . . . 21
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 22
1. Introduction
A Path Segment is a local segment [RFC9545] that uniquely identifies
an SR path on the egress node. A Path Segment Identifier (PSID) is a
single label that is assigned from the Segment Routing Local Block
(SRLB) [RFC8402] of the egress node of an SR path.
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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 pops the PSID.
Procedure for LSP Ping [RFC8029] as defined in Section 7.4 of
[RFC8287] is also applicable to PSID, and this document appends
existing step 4a with a new step 4b specific to PSID. Concretely,
LSP Ping can be used to check the correct operation of a PSID and
verify the PSID against the control plane. Checking correct
operation means that an initiator can use LSP Ping to check whether a
PSID reached the intended node and got processed by that node
correctly. Moreover, verifying a PSID against the control plane
means that the initiator can use LSP Ping to verify the SR Path
context (segment-list, candidate path, or SR policy) associated with
the PSID as signaled or provisioned at the egress node. To that end,
this document specifies six new Target Forwarding Equivalence Class
(FEC) Stack sub-TLVs for such PSID checks.
LSP Traceroute [RFC8287] is left out of this document because transit
nodes are 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],
[RFC8029], and [RFC9545], readers are expected to be familiar with
those terms.
Segment-List-ID
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The Segment-List-ID field is a 4-octet identifier that uniquely
identifies a segment list within the context of the candidate path
of an SR Policy. Although not defined in [RFC9256], the Segment-
List-ID is the same identifier as the one that can be signalled
through control plane procotols including BGP (Section 2.1 of
[I-D.ietf-idr-sr-policy-seglist-id], PCEP (Section 5.2 of
[I-D.ietf-pce-multipath]), and BGP-LS (Section 5.7.4 of
[I-D.ietf-idr-bgp-ls-sr-policy]).
3. Path Segment ID Sub-TLVs
Analogous to what's defined in Section 5 of [RFC8287] and Section 4
of [RFC9703], six 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). Note that the structures of the six
new sub-TLVs follow the TLV's structure defined in Section 3 of
[RFC8029].
+==========+==========================================+
| Sub-Type | Sub-TLV Name |
+==========+==========================================+
| TBD1 | SR Policy Associated PSID - IPv4 |
+----------+------------------------------------------+
| TBD2 | SR Candidate Path Associated PSID - IPv4 |
+----------+------------------------------------------+
| TBD3 | SR Segment List Associated PSID - IPv4 |
+----------+------------------------------------------+
| TBD4 | SR Policy Associated PSID - IPv6 |
+----------+------------------------------------------+
| TBD5 | SR Candidate Path Associated PSID - IPv6 |
+----------+------------------------------------------+
| TBD6 | SR Segment List Associated PSID - IPv6 |
+----------+------------------------------------------+
Table 1: Sub-TLVs for PSID Checks
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 six different Target FEC Stack sub-TLVs need to be defined
for PSID. The ordered list of selection rules for the six Target FEC
Stack sub-TLVs are defined as follows:
* When a PSID is used to identify all segment lists in an SR Policy,
the Target FEC Stack sub-TLV of the type "SR Policy Associated
PSID" (for IPv4 or IPv6) MUST be used for PSID checks.
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* When a PSID is used to identify all segment lists in an SR
Candidate Path, the Target FEC Stack sub-TLV of the type "SR
Candidate Path Associated PSID" (for IPv4 or IPv6) MUST be used
for PSID checks.
* When a PSID is used to identify a Segment List, the Target FEC
Stack sub-TLV of the type "SR Segment List Associated PSID" (for
IPv4 or IPv6) MUST be used for PSID checks.
* When a PSID is used to identify some segment lists in a Candidate
path or an SR policy, the Target FEC Stack sub-TLV of the type "SR
Segment List Associated PSID" (for IPv4 or IPv6) MUST be used for
PSID checks. In this case, multiple LSP Ping messages MUST be
sent, and one Target FEC Stack sub-TLV of the type "SR Segment
List Associated PSID" (for IPv4 or IPv6) MUST be carried in each
LSP Ping message.
These six new Target FEC Stack sub-TLVs are not expected to be
present in the same message. If more than one of these sub-TLVs are
present in a message, only the first sub-TLV will be processed per
the validation rules in Section 4.
3.1. SR Policy Associated PSID - IPv4 Sub-TLV
The SR Policy Associated PSID - IPv4 sub-TLV is defined as follows:
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 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Color (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Endpoint (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: SR Policy Associated PSID - IPv4 sub-TLV Format
Type (length: 2 octets)
The Type field identifies the sub-TLV as an SR Policy Associated
PSID - IPv4 Sub-TLV. The value is set to (TBD1) and is to be
assigned by IANA.
Length (length: 2 octets)
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The Length field indicates the length of the sub-TLV in octets,
excluding the first 4 octets (Type and Length fields). The value
MUST be set to 12.
Headend (length: 4 octets)
The Headend field encodes the headend IPv4 address of the SR
Policy. This field is defined in Section 2.1 of [RFC9256].
Color (length: 4 octets)
The Color field identifies the color (i.e., policy identifier) of
the SR Policy and is encoded as defined in Section 2.1 of
[RFC9256].
Endpoint (length: 4 octets)
The Endpoint field encodes the endpoint IPv4 address of the SR
Policy. This field is defined in Section 2.1 of [RFC9256].
3.2. SR Candidate Path Associated PSID - IPv4 Sub-TLV
The SR Candidate Path Associated PSID - IPv4 sub-TLV is defined as
follows:
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 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Color (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Endpoint (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Protocol-Origin| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| |
| Originator (20 octets) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Discriminator (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Figure 2: SR Candidate Path Associated PSID - IPv4 sub-TLV Format
Type (length: 2 octets)
The Type field identifies the sub-TLV as an SR Candidate Path
Associated PSID - IPv4 sub-TLV. The value is set to (TBD2) and is
to be assigned by IANA.
Length (length: 2 octets)
The Length field indicates the length of the sub-TLV in octets,
excluding the first 4 octets (Type and Length fields). The value
MUST be set to 40.
Headend (length: 4 octets)
The Headend field encodes the headend IPv4 address of the SR
Candidate Path. This field is defined in Section 2.1 of
[RFC9256].
Color (length: 4 octets)
The Color field identifies the policy color and is defined in
Section 2.1 of [RFC9256].
Endpoint (length: 4 octets)
The Endpoint field encodes the endpoint IPv4 address of the SR
Candidate Path. This field is defined in Section 2.1 of
[RFC9256].
Protocol-Origin (length: 1 octet)
The Protocol-Origin field indicates the protocol that originated
the SR Candidate Path. It is defined in Section 2.3 of [RFC9256]
and takes values from the IANA registry [PROTOCOL-ORIGIN]. If an
unsupported value is used, validation at the responder MUST fail.
Reserved (length: 3 octets)
The Reserved field is reserved for future use. It MUST be set to
zero when sent and MUST be ignored upon receipt.
Originator (length: 20 octets)
The Originator field identifies the originator of the SR Candidate
Path and is encoded as defined in Section 2.4 of [RFC9256].
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Discriminator (length: 4 octets)
The Discriminator field uniquely identifies the SR Candidate Path
within the context of the Headend, Color, and Endpoint. This
field is defined in Section 2.5 of [RFC9256].
3.3. SR Segment List Associated PSID - IPv4 Sub-TLV
The SR Segment List Associated PSID - IPv4 sub-TLV is used to
identify a specific segment list within the context of a candidate
path of an SR Policy. The format of this sub-TLV is shown in
Figure 3.
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 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Color (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Endpoint (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Protocol-Origin| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| |
| Originator (20 octets) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Discriminator (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Segment-List-ID (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: SR Segment List Associated PSID - IPv4 sub-TLV Format
Type (length: 2 octets)
The Type field identifies the sub-TLV as an SR Segment List
Associated PSID - IPv4 sub-TLV. The value is set to (TBD3) and is
to be assigned by IANA.
Length (length: 2 octets)
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The Length field indicates the length of the sub-TLV in octets,
excluding the first 4 octets (Type and Length fields). The value
MUST be set to 44.
Headend (length: 4 octets)
The Headend field encodes the headend IPv4 address of the SR
Policy. This field is defined in Section 2.1 of [RFC9256].
Color (length: 4 octets)
The Color field identifies the color of the SR Policy and is
encoded as specified in Section 2.1 of [RFC9256].
Endpoint (length: 4 octets)
The Endpoint field specifies the endpoint IPv4 address of the SR
Policy, as defined in Section 2.1 of [RFC9256].
Protocol-Origin (length: 1 octet)
The Protocol-Origin field indicates the protocol that originated
the SR Candidate Path. It is defined in Section 2.3 of [RFC9256]
and takes values from the IANA registry [PROTOCOL-ORIGIN]. If an
unsupported value is used, validation at the responder MUST fail.
Reserved (length: 3 octets)
The Reserved field is reserved for future use. It MUST be set to
zero when transmitted and MUST be ignored upon receipt.
Originator (length: 20 octets)
The Originator field identifies the originator of the SR Candidate
Path and is defined in Section 2.4 of [RFC9256].
Discriminator (length: 4 octets)
The Discriminator field uniquely identifies the SR Candidate Path
within the context of the Headend, Color, and Endpoint. This
field is defined in Section 2.5 of [RFC9256].
Segment-List-ID (length: 4 octets)
The Segment-List-ID field is a 4-octet identifier that uniquely
identifies a segment list within the context of the candidate path
of an SR Policy. This field is defined in terminology of
Section 2.2.
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3.4. SR Policy Associated PSID - IPv6 Sub-TLV
The SR Policy Associated PSID - IPv6 sub-TLV is defined as follows:
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 = TBD4 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Headend (16 octets) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Color (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Endpoint (16 octets) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: SR Policy Associated PSID - IPv6 sub-TLV Format
Type (length: 2 octets)
The Type field identifies the sub-TLV as an SR Policy Associated
PSID - IPv6 Sub-TLV. The value is set to (TBD4) and is to be
assigned by IANA.
Length (length: 2 octets)
The Length field indicates the length of the sub-TLV in octets,
excluding the first 4 octets (Type and Length fields). The value
MUST be set to 36.
Headend (length: 16 octets)
The Headend field encodes the headend IPv6 address of the SR
Policy. This field is defined in Section 2.1 of [RFC9256].
Color (length: 4 octets)
The Color field identifies the color (i.e., policy identifier) of
the SR Policy and is encoded as defined in Section 2.1 of
[RFC9256].
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Endpoint (length: 16 octets)
The Endpoint field encodes the endpoint IPv6 address of the SR
Policy. This field is defined in Section 2.1 of [RFC9256].
3.5. SR Candidate Path Associated PSID - IPv6 Sub-TLV
The SR Candidate Path Associated PSID - IPv6 sub-TLV is defined as
follows:
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 = TBD5 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Headend (16 octets) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Color (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Endpoint (16 octets) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Protocol-Origin| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| |
| Originator (20 octets) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Discriminator (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: SR Candidate Path Associated PSID - IPv6 sub-TLV Format
Type (length: 2 octets)
The Type field identifies the sub-TLV as an SR Candidate Path
Associated PSID - IPv6 sub-TLV. The value is set to (TBD5) and is
to be assigned by IANA.
Length (length: 2 octets)
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The Length field indicates the length of the sub-TLV in octets,
excluding the first 4 octets (Type and Length fields). The value
MUST be set to 64.
Headend (length: 16 octets)
The Headend field encodes the headend IPv6 address of the SR
Candidate Path. This field is defined in Section 2.1 of
[RFC9256].
Color (length: 4 octets)
The Color field identifies the policy color and is defined in
Section 2.1 of [RFC9256].
Endpoint (length: 16 octets)
The Endpoint field encodes the endpoint IPv6 address of the SR
Candidate Path. This field is defined in Section 2.1 of
[RFC9256].
Protocol-Origin (length: 1 octet)
The Protocol-Origin field indicates the protocol that originated
the SR Candidate Path. It is defined in Section 2.3 of [RFC9256]
and takes values from the IANA registry [PROTOCOL-ORIGIN]. If an
unsupported value is used, validation at the responder MUST fail.
Reserved (length: 3 octets)
The Reserved field is reserved for future use. It MUST be set to
zero when sent and MUST be ignored upon receipt.
Originator (length: 20 octets)
The Originator field identifies the originator of the SR Candidate
Path and is encoded as defined in Section 2.4 of [RFC9256].
Discriminator (length: 4 octets)
The Discriminator field uniquely identifies the SR Candidate Path
within the context of the Headend, Color, and Endpoint. This
field is defined in Section 2.5 of [RFC9256].
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3.6. SR Segment List Associated PSID - IPv6 Sub-TLV
The SR Segment List Associated PSID - IPv6 sub-TLV is used to
identify a specific segment list within the context of a candidate
path of an SR Policy. The format of this sub-TLV is shown in
Figure 6.
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 = TBD6 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Headend (16 octets) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Color (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Endpoint (16 octets) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Protocol-Origin| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| |
| Originator (20 octets) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Discriminator (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Segment-List-ID (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: SR Segment List Associated PSID - IPv6 sub-TLV Format
Type (length: 2 octets)
The Type field identifies the sub-TLV as an SR Segment List
Associated PSID - IPv6 sub-TLV. The value is set to (TBD6) and is
to be assigned by IANA.
Length (length: 2 octets)
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The Length field indicates the length of the sub-TLV in octets,
excluding the first 4 octets (Type and Length fields). The value
MUST be set to 68.
Headend (length: 16 octets)
The Headend field encodes the headend IPv6 address of the SR
Policy. This field is defined in Section 2.1 of [RFC9256].
Color (length: 4 octets)
The Color field identifies the color of the SR Policy and is
encoded as specified in Section 2.1 of [RFC9256].
Endpoint (length: 16 octets)
The Endpoint field specifies the endpoint IPv6 address of the SR
Policy, as defined in Section 2.1 of [RFC9256].
Protocol-Origin (length: 1 octet)
The Protocol-Origin field indicates the protocol that originated
the SR Candidate Path. It is defined in Section 2.3 of [RFC9256]
and takes values from the IANA registry [PROTOCOL-ORIGIN]. If an
unsupported value is used, validation at the responder MUST fail.
Reserved (length: 3 octets)
The Reserved field is reserved for future use. It MUST be set to
zero when transmitted and MUST be ignored upon receipt.
Originator (length: 20 octets)
The Originator field identifies the originator of the SR Candidate
Path and is defined in Section 2.4 of [RFC9256].
Discriminator (length: 4 octets)
The Discriminator field uniquely identifies the SR Candidate Path
within the context of the Headend, Color, and Endpoint. This
field is defined in Section 2.5 of [RFC9256].
Segment-List-ID (length: 4 octets)
The Segment-List-ID field is a 4-octet identifier that uniquely
identifies a segment list within the context of the candidate path
of an SR Policy. This field is defined in terminology of
Section 2.2.
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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 SR 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.
If a malformed FEC Stack sub-TLV is received, then a return code of
1, "Malformed echo request received" as defined in [RFC8029] MUST be
sent. The section below is appended to step 4a of Section 7.4 of
[RFC8287].
4.1. PSID FEC Validation Rules
4b. Segment Routing PSID Validation:
If the Label-stack-depth is 1 and the Target FEC Stack sub-TLV at
FEC-stack-depth is TBD1 (SR Policy Associated PSID - IPv4 sub-TLV), {
Set the Best-return-code to 10, "Mapping for this FEC is not the
given label at stack-depth <RSC>" if any below conditions fail
(the notation <RSC> refers to the Return Subcode):
- Validate that the PSID is signaled or provisioned for the SR
Policy {
o Validate that the signaled or provisioned headend, color,
and endpoint, for the PSID, matches with the corresponding
fields in the received SR Policy Associated PSID - IPv4 sub-
TLV.
}
}
If all the above validations have passed, set the return code to 3
"Replying router is an egress for the FEC at stack-depth <RSC>".
Set FEC-Status to 1 and return.
}
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Else, if the Label-stack-depth is 1 and the Target FEC Stack sub-TLV
at FEC-stack-depth is TBD2 (SR Candidate Path Associated PSID - IPv4
sub-TLV), {
Set the Best-return-code to 10, "Mapping for this FEC is not the
given label at stack-depth <RSC>" if any below conditions fail:
- Validate that the PSID is signaled or provisioned for the SR
Candidate Path {
o Validate that the signaled or provisioned headend, color,
endpoint, originator, and discriminator, for the PSID,
matches with the corresponding fields in the received SR
Candidate Path Associated PSID - IPv4 sub-TLV.
}
}
If all the above validations have passed, set the return code to 3
"Replying router is an egress for the FEC at stack-depth <RSC>".
Set FEC-Status to 1 and return.
}
Else, if the Label-stack-depth is 1 and the Target FEC Stack sub-TLV
at FEC-stack-depth is TBD3 (SR Segment List Associated PSID - IPv4
sub-TLV), {
Set the Best-return-code to 10, "Mapping for this FEC is not the
given label at stack-depth <RSC>" if any below conditions fail:
- Validate that the PSID is signaled or provisioned for the SR
Segment List {
o Validate that the signaled or provisioned headend, color,
endpoint, originator, discriminator, and segment-list-id,
for the PSID, matches with the corresponding fields in the
received SR Segment List Associated PSID - IPv4 sub-TLV.
}
}
If all the above validations have passed, set the return code to 3
"Replying router is an egress for the FEC at stack-depth <RSC>".
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Set FEC-Status to 1 and return.
}
Else, if the Label-stack-depth is 1 and the Target FEC Stack sub-TLV
at FEC-stack-depth is TBD4 (SR Policy Associated PSID - IPv6 sub-
TLV), {
Set the Best-return-code to 10, "Mapping for this FEC is not the
given label at stack-depth <RSC>" if any below conditions fail
(the notation <RSC> refers to the Return Subcode):
- Validate that the PSID is signaled or provisioned for the SR
Policy {
o Validate that the signaled or provisioned headend, color,
and endpoint, for the PSID, matches with the corresponding
fields in the received SR Policy Associated PSID - IPv6 sub-
TLV.
}
}
If all the above validations have passed, set the return code to 3
"Replying router is an egress for the FEC at stack-depth <RSC>".
Set FEC-Status to 1 and return.
}
Else, if the Label-stack-depth is 1 and the Target FEC Stack sub-TLV
at FEC-stack-depth is TBD5 (SR Candidate Path Associated PSID - IPv6
sub-TLV), {
Set the Best-return-code to 10, "Mapping for this FEC is not the
given label at stack-depth <RSC>" if any below conditions fail:
- Validate that the PSID is signaled or provisioned for the SR
Candidate Path {
o Validate that the signaled or provisioned headend, color,
endpoint, originator, and discriminator, for the PSID,
matches with the corresponding fields in the received SR
Candidate Path Associated PSID - IPv6 sub-TLV.
}
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}
If all the above validations have passed, set the return code to 3
"Replying router is an egress for the FEC at stack-depth <RSC>".
Set FEC-Status to 1 and return.
}
Else, if the Label-stack-depth is 1 and the Target FEC Stack sub-TLV
at FEC-stack-depth is TBD6 (SR Segment List Associated PSID - IPv6
sub-TLV), {
Set the Best-return-code to 10, "Mapping for this FEC is not the
given label at stack-depth <RSC>" if any below conditions fail:
- Validate that the PSID is signaled or provisioned for the SR
Segment List {
o Validate that the signaled or provisioned headend, color,
endpoint, originator, discriminator, and segment-list-id,
for the PSID, matches with the corresponding fields in the
received SR Segment List Associated PSID - IPv6 sub-TLV.
}
}
If all the above validations have passed, set the return code to 3
"Replying router is an egress for the FEC at stack-depth <RSC>".
Set FEC-Status to 1 and return.
}
When an SR Policy Associated PSID - IPv4 sub-TLV, or an SR Candidate
Path Associated PSID - IPv4 sub-TLV, or an SR Segment List Associated
PSID - IPv4 sub-TLV, or an SR Policy Associated PSID - IPv6 sub-TLV,
or an SR Candidate Path Associated PSID - IPv6 sub-TLV, or an SR
Segment List Associated PSID - IPv6 sub-TLV 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.
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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 Section 5 of [RFC8029] apply to this document. 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 six new Target FEC Stack sub-TLVs from
the "Sub-TLVs for TLV Types 1, 16, and 21" registry [MPLS-LSP-PING]
within the "TLVs" registry of the "Multiprotocol Label Switching
(MPLS) Label Switched Paths (LSPs) Ping Parameters" registry group.
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 Associated PSID - IPv4 | Section 3.1 of |
| | | THIS_DOCUMENT |
+----------+----------------------------------+----------------+
| TBD2 | SR Candidate Path Associated | Section 3.2 of |
| | PSID - IPv4 | THIS_DOCUMENT |
+----------+----------------------------------+----------------+
| TBD3 | SR Segment List Associated PSID | Section 3.3 of |
| | - IPv4 | THIS_DOCUMENT |
+----------+----------------------------------+----------------+
| TBD4 | SR Policy Associated PSID - IPv6 | Section 3.4 of |
| | | THIS_DOCUMENT |
+----------+----------------------------------+----------------+
| TBD5 | SR Candidate Path Associated | Section 3.5 of |
| | PSID - IPv6 | THIS_DOCUMENT |
+----------+----------------------------------+----------------+
| TBD6 | SR Segment List Associated PSID | Section 3.6 of |
| | - IPv6 | THIS_DOCUMENT |
+----------+----------------------------------+----------------+
Table 2: Sub-TLVs for TLV Types 1, 16, and 21 Registry
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7. Acknowledgements
The authors would like to acknowledge Loa Andersson, Detao Zhao, Ben
Niven-Jenkins, Greg Mirsky, Ketan Talaulikar, James Guichard, Jon
Geater, Gorry Fairhurst, Bing Liu, Mohamed Boucadair, Eric Vyncke,
Gunter Van de Velde, Mahesh Jethanandani, and Andy Smith for their
thorough review and very helpful comments.
The authors would like to acknowledge Yao Liu and Quan Xiong for the
very helpful face to face discussion.
8. References
8.1. Normative References
[MPLS-LSP-PING]
"Multi-Protocol Label Switching (MPLS) Label Switched
Paths (LSPs) Ping Parameters",
<http://www.iana.org/assignments/mpls-lsp-ping-
parameters>.
[PROTOCOL-ORIGIN]
"SR Policy Protocol Origin",
<https://www.iana.org/assignments/segment-routing/segment-
routing.xhtml#sr-policy-protocol-origin>.
[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>.
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[RFC9256] Filsfils, C., Talaulikar, K., Ed., Voyer, D., Bogdanov,
A., and P. Mattes, "Segment Routing Policy Architecture",
RFC 9256, DOI 10.17487/RFC9256, July 2022,
<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,
February 2024, <https://www.rfc-editor.org/info/rfc9545>.
8.2. Informative References
[I-D.ietf-idr-bgp-ls-sr-policy]
Previdi, S., Talaulikar, K., Dong, J., Gredler, H., and J.
Tantsura, "Advertisement of Segment Routing Policies using
BGP Link-State", Work in Progress, Internet-Draft, draft-
ietf-idr-bgp-ls-sr-policy-17, 6 March 2025,
<https://datatracker.ietf.org/doc/html/draft-ietf-idr-bgp-
ls-sr-policy-17>.
[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-04, 27 March 2025,
<https://datatracker.ietf.org/doc/html/draft-ietf-idr-sr-
policy-seglist-id-04>.
[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-13, 9
April 2025, <https://datatracker.ietf.org/doc/html/draft-
ietf-pce-multipath-13>.
[RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
Label Switching Architecture", RFC 3031,
DOI 10.17487/RFC3031, January 2001,
<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,
July 2018, <https://www.rfc-editor.org/info/rfc8402>.
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[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, July
2018, <https://www.rfc-editor.org/info/rfc8403>.
[RFC9703] Hegde, S., Srivastava, M., Arora, K., Ninan, S., and X.
Xu, "Label Switched Path (LSP) Ping/Traceroute for Segment
Routing (SR) Egress Peer Engineering (EPE) Segment
Identifiers (SIDs) with MPLS Data Plane", RFC 9703,
DOI 10.17487/RFC9703, December 2024,
<https://www.rfc-editor.org/info/rfc9703>.
Authors' Addresses
Xiao Min
ZTE Corp.
Nanjing
China
Phone: +86 18061680168
Email: xiao.min2@zte.com.cn
Shaofu Peng
ZTE Corp.
Nanjing
China
Email: peng.shaofu@zte.com.cn
Liyan Gong
China Mobile
Beijing
China
Email: gongliyan@chinamobile.com
Rakesh Gandhi
Cisco Systems, Inc.
Canada
Email: rgandhi@cisco.com
Carlos Pignataro
Blue Fern Consulting
United States of America
Email: carlos@bluefern.consulting, cpignata@gmail.com
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