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IETF RFC 9831
Last modified on Friday, September 12th, 2025
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Internet Engineering Task Force (IETF) K. Talaulikar, Ed.
Request for Comments: 9831 C. Filsfils
Category: Experimental Cisco Systems
ISSN: 2070-1721 S. Previdi
Huawei Technologies
P. Mattes
Microsoft
D. Jain
Google
September 2025
Segment Type Extensions for BGP Segment Routing (SR) Policy
 Abstract
This document specifies the signaling of additional Segment Routing
(SR) Segment Types for SR Policies in BGP using the SR Policy
Subsequent Address Family Identifier (SAFI).
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for examination, experimental implementation, and
evaluation.
This document defines an Experimental Protocol for the Internet
community. 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). Not
all documents approved by the IESG are candidates for any level of
Internet Standard; see 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/RFC 9831.
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
1.1. Requirements Language
2. Segment Type Sub-TLVs
2.1. Segment Type C
2.2. Segment Type D
2.3. Segment Type E
2.4. Segment Type F
2.5. Segment Type G
2.6. Segment Type H
2.7. Segment Type I
2.8. Segment Type J
2.9. Segment Type K
2.10. SR Policy Segment Flags
3. IANA Considerations
3.1. SR Policy Segment List Sub-TLVs
3.2. SR Policy Segment Flags
4. Security Considerations
5. Manageability Considerations
6. Normative References
Acknowledgments
Authors' Addresses
1. Introduction
The BGP Segment Routing (SR) Policy Subsequent Address Family
Identifier (SAFI) was introduced by [RFC 9830] for the advertisement
of SR Policies [RFC 8402]. [RFC 9830] introduced the base SR Segment
Types A and B as specified by the SR Policy Architecture [RFC 9256].
This document specifies the extensions for the advertisement of the
remaining SR Segment Types defined in [RFC 9256] in the SR Policy SAFI
for both SR-MPLS (see [RFC 8660]) and Segment Routing over IPv6 (SRv6)
(see [RFC 8754] and [RFC 8986]).
The extensions in this document do not impact the SR Policy
operations or fault management as specified in [RFC 9830].
1.1. 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 [RFC 2119] [RFC 8174] when, and only when, they appear in all
capitals, as shown here.
2. Segment Type Sub-TLVs
The Segment List sub-TLV [RFC 9830] encodes a single explicit path
towards the endpoint as described in Section 5.1 of [RFC 9256]. The
Segment List sub-TLV includes the elements of the paths (i.e.,
segments).
A Segment sub-TLV describes a single segment in a segment list (i.e.,
a single element of the explicit path).
Section 4 of [RFC 9256] defines several Segment Types for SR-MPLS and
SRv6 that are listed below as a reminder:
Type A: SR-MPLS Label
Type B: SRv6 SID
Type C: IPv4 Prefix with optional SR Algorithm
Type D: IPv6 Global Prefix with optional SR Algorithm for SR-MPLS
Type E: IPv4 Prefix with Local Interface ID
Type F: IPv4 Addresses for link endpoints as Local, Remote pair
Type G: IPv6 Prefix and Interface ID for link endpoints as Local,
Remote pair for SR-MPLS
Type H: IPv6 Addresses for link endpoints as Local, Remote pair for
SR-MPLS
Type I: IPv6 Global Prefix with optional SR Algorithm for SRv6
Type J: IPv6 Prefix and Interface ID for link endpoints as Local,
Remote pair for SRv6
Type K: IPv6 Addresses for link endpoints as Local, Remote pair for
SRv6
[RFC 9830] specifies Segment Type Sub-TLVs for the Segment Types A and
B. The following subsections specify the sub-TLVs used for encoding
each of the other Segment Types above.
As specified in Sections 2.4.4 and 2.4.4.2 of [RFC 9830], validation
of an explicit path encoded by the Segment List sub-TLV is beyond the
scope of BGP and performed by the Segment Routing Policy Module
(SRPM) as described in Section 5 of [RFC 9830]. As specified in
Section 5.1 of [RFC 9256], a mix of SR-MPLS and SRv6 segments make the
segment-list invalid.
2.1. Segment Type C
The Type C Segment sub-TLV encodes an IPv4 node address, SR
Algorithm, and an optional SR-MPLS Segment Identifier (SID). The
format is 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 | Length | Flags | SR Algorithm |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 Node Address (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SR-MPLS SID (optional, 4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Type C Segment Sub-TLV
Where:
Type: 3
Length: Specifies the length of the value field (i.e., not including
Type and Length fields) in terms of octets. The value MUST be 10
when the SR-MPLS SID is present; else, it MUST be 6.
Flags: 1 octet of flags as defined in Section 2.10.
SR Algorithm: 1 octet specifying the SR Algorithm as described in
Section 3.1.1 of [RFC 8402] when the A-Flag as defined in
Section 2.10 is set. The SR Algorithm is used by the SRPM
[RFC 9830] as described in Section 4 of [RFC 9256]. When the A-Flag
is not set, this field MUST be set to zero on transmission and
MUST be ignored on receipt.
IPv4 Node Address: A 4-octet IPv4 address representing a node.
SR-MPLS SID: Optional. A 4-octet field containing a label, Traffic
Class (TC), bottom-of-stack (S), and TTL as defined for Segment
Type A [RFC 9830].
2.2. Segment Type D
The Type D Segment sub-TLV encodes an IPv6 node address, SR
Algorithm, and an optional SR-MPLS SID. The format is 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 | Length | Flags | SR Algorithm |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// IPv6 Node Address (16 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SR-MPLS SID (optional, 4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Type D Segment Sub-TLV
Where:
Type: 4
Length: Specifies the length of the value field (i.e., not including
Type and Length fields) in terms of octets. The value MUST be 22
when the SR-MPLS SID is present; else, it MUST be 18.
Flags: 1 octet of flags as defined in Section 2.10.
SR Algorithm: 1 octet specifying the SR Algorithm as described in
Section 3.1.1 of [RFC 8402] when the A-Flag as defined in
Section 2.10 is set. The SR Algorithm is used by the SRPM
[RFC 9830] as described in Section 4 of [RFC 9256]. When the A-Flag
is not set, this field MUST be set to zero on transmission and
MUST be ignored on receipt.
IPv6 Node Address: A 16-octet IPv6 address representing a node.
SR-MPLS SID: Optional. A 4-octet field containing a label, TC, S,
and TTL as defined for Segment Type A [RFC 9830].
2.3. Segment Type E
The Type E Segment sub-TLV encodes an IPv4 node address, a local
interface Identifier (Local Interface ID), and an optional SR-MPLS
SID. The format is 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 | Length | Flags | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Local Interface ID (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 Node Address (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SR-MPLS SID (optional, 4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Type E Segment Sub-TLV
Where:
Type: 5
Length: Specifies the length of the value field (i.e., not including
Type and Length fields) in terms of octets. The value MUST be 14
when the SR-MPLS SID is present; else, it MUST be 10.
Flags: 1 octet of flags as defined in Section 2.10.
RESERVED: 1 octet of reserved bits. This field MUST be set to zero
on transmission and MUST be ignored on receipt.
Local Interface ID: 4 octets carrying the interface index of the
local interface (refer to TLV 258 of [RFC 9552]).
IPv4 Node Address: A 4-octet IPv4 address representing a node.
SR-MPLS SID: Optional. A 4-octet field containing a label, TC, S,
and TTL as defined for Segment Type A [RFC 9830].
2.4. Segment Type F
The Type F Segment sub-TLV encodes an adjacency local address, an
adjacency remote address, and an optional SR-MPLS SID. The format is
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 | Length | Flags | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Local IPv4 Address (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remote IPv4 Address (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SR-MPLS SID (optional, 4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: Type F Segment Sub-TLV
Where:
Type: 6
Length: Specifies the length of the value field (i.e., not including
Type and Length fields) in terms of octets. The value MUST be 14
when the SR-MPLS SID is present; else, it MUST be 10.
Flags: 1 octet of flags as defined in Section 2.10.
RESERVED: 1 octet of reserved bits. This field MUST be set to zero
on transmission and MUST be ignored on receipt.
Local IPv4 Address: A 4-octet IPv4 address representing the local
link address of the node.
Remote IPv4 Address: A 4-octet IPv4 address representing the link
address of the neighbor node.
SR-MPLS SID: Optional. A 4-octet field containing a label, TC, S,
and TTL as defined for Segment Type A [RFC 9830].
2.5. Segment Type G
The Type G Segment sub-TLV encodes an IPv6 link-local adjacency with
an IPv6 local node address, a local interface identifier (Local
Interface ID), an IPv6 remote node address, a remote interface
identifier (Remote Interface ID), and an optional SR-MPLS SID. The
format is 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 | Length | Flags | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Local Interface ID (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// IPv6 Local Node Address (16 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remote Interface ID (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// IPv6 Remote Node Address (16 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SR-MPLS SID (optional, 4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: Type G Segment Sub-TLV
Where:
Type: 7
Length: Specifies the length of the value field (i.e., not including
Type and Length fields) in terms of octets. The value MUST be 46
when the SR-MPLS SID is present; else, it MUST be 42.
Flags: 1 octet of flags as defined in Section 2.10.
RESERVED: 1 octet of reserved bits. This field MUST be set to zero
on transmission and MUST be ignored on receipt.
Local Interface ID: 4 octets of interface index of local interface
(refer to TLV 258 of [RFC 9552]).
IPv6 Local Node Address: A 16-octet IPv6 address representing the
node.
Remote Interface ID: 4 octets of interface index of remote interface
(refer to TLV 258 of [RFC 9552]). The value MAY be set to zero
when the local node address and interface identifiers are
sufficient to describe the link.
IPv6 Remote Node Address: A 16-octet IPv6 address. The value MAY be
set to zero when the local node address and interface identifiers
are sufficient to describe the link.
SR-MPLS SID: Optional. A 4-octet field containing a label, TC, S,
and TTL as defined for Segment Type A [RFC 9830].
2.6. Segment Type H
The Type H Segment sub-TLV encodes an adjacency local address, an
adjacency remote address, and an optional SR-MPLS SID. The format is
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 | Length | Flags | RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Local IPv6 Address (16 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Remote IPv6 Address (16 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SR-MPLS SID (optional, 4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: Type H Segment Sub-TLV
Where:
Type: 8
Length: Specifies the length of the value field (i.e., not including
Type and Length fields) in terms of octets. The value MUST be 38
when the SR-MPLS SID is present; else, it MUST be 34.
Flags: 1 octet of flags as defined in Section 2.10.
RESERVED: 1 octet of reserved bits. This field MUST be set to zero
on transmission and MUST be ignored on receipt.
Local IPv6 Address: A 16-octet IPv6 address representing the local
link address of the node.
Remote IPv6 Address: A 16-octet IPv6 address representing the link
address of the neighbor node.
SR-MPLS SID: Optional. A 4-octet field containing a label, TC, S,
and TTL as defined for Segment Type A [RFC 9830].
2.7. Segment Type I
The Type I Segment sub-TLV encodes an IPv6 node address, an SR
Algorithm, and an optional SRv6 SID. The format is 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 | Length | Flags | SR Algorithm |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// IPv6 Node Address (16 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// SRv6 SID (optional, 16 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// SRv6 Endpoint Behavior and SID Structure //
// (optional, 8 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: Type I Segment Sub-TLV
Where:
Type: 14
Length: Specifies the length of the value field (i.e., not including
Type and Length fields) in terms of octets. The value MUST be one
of the following:
* 42 when both SRv6 SID and SRv6 Endpoint Behavior and SID
Structure are present,
* 34 when only SRv6 SID is present, or
* 18 when the SRv6 SID is not present.
Flags: 1 octet of flags as defined in Section 2.10.
SR Algorithm: 1 octet specifying the SR Algorithm as described in
Section 3.1.1 of [RFC 8402] when the A-Flag as defined in
Section 2.10 is set. The SR Algorithm is used by the SRPM
[RFC 9830] as described in Section 4 of [RFC 9256]. When the A-Flag
is not set, this field MUST be set to zero on transmission and
MUST be ignored on receipt.
IPv6 Node Address: A 16-octet IPv6 address representing the node.
SRv6 SID: Optional. A 16-octet IPv6 address. The value 0 MAY be
used when the controller wants to indicate the desired SRv6
Endpoint Behavior or SID Structure without specifying the SID.
SRv6 Endpoint Behavior and SID Structure: Optional, as defined in
Section 2.4.4.2.4 of [RFC 9830]. The SRv6 Endpoint Behavior or SID
Structure MUST NOT be included when the SRv6 SID has not been
included.
TLV 10 defined for the advertisement of Segment Type I in the early
draft versions of [RFC 9830] has been deprecated to avoid backward-
compatibility issues.
2.8. Segment Type J
The Type J Segment sub-TLV encodes an IPv6 link-local adjacency with
a local node address, a local interface identifier (Local Interface
ID), a remote IPv6 node address, a remote interface identifier
(Remote Interface ID), and an optional SRv6 SID. The format is 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 | Length | Flags | SR Algorithm |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Local Interface ID (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// IPv6 Local Node Address (16 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remote Interface ID (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// IPv6 Remote Node Address (16 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// SRv6 SID (optional, 16 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// SRv6 Endpoint Behavior and SID Structure //
// (optional, 8 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8: Type J Segment Sub-TLV
Where:
Type: 15
Length: Specifies the length of the value field (i.e., not including
Type and Length fields) in terms of octets. The value MUST be one
of the following:
* 66 when both SRv6 SID and SRv6 Endpoint Behavior and SID
Structure are present,
* 58 when only SRv6 SID is present, or
* 42 when the SRv6 SID is not present.
Flags: 1 octet of flags as defined in Section 2.10.
SR Algorithm: 1 octet specifying the SR Algorithm as described in
Section 3.1.1 of [RFC 8402] when the A-Flag as defined in
Section 2.10 is set. The SR Algorithm is used by the SRPM
[RFC 9830] as described in Section 4 of [RFC 9256]. When the A-Flag
is not set, this field MUST be set to zero on transmission and
MUST be ignored on receipt.
Local Interface ID: 4 octets of interface index of local interface
(refer to TLV 258 of [RFC 9552]).
IPv6 Local Node Address: A 16-octet IPv6 address representing the
node.
Remote Interface ID: 4 octets of interface index of remote interface
(refer to TLV 258 of [RFC 9552]). The value MAY be set to zero
when the local node address and interface identifiers are
sufficient to describe the link.
IPv6 Remote Node Address: A 16-octet IPv6 address. The value MAY be
set to zero when the local node address and interface identifiers
are sufficient to describe the link.
SRv6 SID: Optional. A 16-octet IPv6 address. The value 0 MAY be
used when the controller wants to indicate the desired SRv6
Endpoint Behavior or SID Structure without specifying the SID.
SRv6 Endpoint Behavior and SID Structure: Optional, as defined in
Section 2.4.4.2.4 of [RFC 9830]. The SRv6 Endpoint Behavior and
SID Structure MUST NOT be included when the SRv6 SID has not been
included.
TLV 11 defined for the advertisement of Segment Type J in the early
draft versions of [RFC 9830] has been deprecated to avoid backward-
compatibility issues.
2.9. Segment Type K
The Type K Segment sub-TLV encodes an adjacency local address, an
adjacency remote address, and an optional SRv6 SID. The format is 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 | Length | Flags | SR Algorithm |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Local IPv6 Address (16 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Remote IPv6 Address (16 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// SRv6 SID (optional, 16 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// SRv6 Endpoint Behavior and SID Structure //
// (optional, 8 octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 9: Type K Segment Sub-TLV
Where:
Type: 16
Length: Specifies the length of the value field (i.e., not including
Type and Length fields) in terms of octets. The value MUST be one
of the following:
* 58 when both SRv6 SID and SRv6 Endpoint Behavior and SID
Structure are present,
* 50 when only SRv6 SID is present, or
* 34 when the SRv6 SID is not present.
Flags: 1 octet of flags as defined in Section 2.10.
SR Algorithm: 1 octet specifying the SR Algorithm as described in
Section 3.1.1 of [RFC 8402] when the A-Flag as defined in
Section 2.10 is set. The SR Algorithm is used by the SRPM
[RFC 9830] as described in Section 4 of [RFC 9256]. When the A-Flag
is not set, this field MUST be set to zero on transmission and
MUST be ignored on receipt.
Local IPv6 Address: A 16-octet IPv6 address representing the local
link address of the node.
Remote IPv6 Address: A 16-octet IPv6 address representing the link
address of the neighbor node.
SRv6 SID: Optional. A 16-octet IPv6 address. The value 0 MAY be
used when the controller wants to indicate the desired SRv6
Endpoint Behavior or SID Structure without specifying the SID.
SRv6 Endpoint Behavior and SID Structure: Optional, as defined in
Section 2.4.4.2.4 of [RFC 9830]. The SRv6 Endpoint Behavior and
SID Structure MUST NOT be included when the SRv6 SID has not been
included.
TLV 12 defined for the advertisement of Segment Type K in the early
draft versions of [RFC 9830] has been deprecated to avoid backward-
compatibility issues.
2.10. SR Policy Segment Flags
The Segment Type sub-TLVs described above may contain the following
SR Policy Segment Flags [RFC 9830] in their Flags field (see also
Section 3.2). This document introduces additional flags below:
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|V|A|S|B| |
+-+-+-+-+-+-+-+-+
Figure 10: SR Policy Segment Flags
Where:
V-Flag: This is an existing flag as defined in [RFC 9830].
A-Flag: When set, this flag indicates the presence of the SR
Algorithm id in the SR Algorithm field applicable to various
Segment Types. The SR Algorithm is used by the SRPM [RFC 9830] as
described in Section 4 of [RFC 9256].
S-Flag: When set, this flag indicates the presence of the SR-MPLS or
SRv6 SID depending on the segment type.
B-Flag: This is an existing flag as defined in [RFC 9830].
The following applies to the Segment Flags:
* The V-Flag applies to all Segment Types including those introduced
by this document.
* The A-Flag applies to Segment Types C, D, I, J, and K. The value
of the A-Flag MUST be ignored for Segment Types A, B, E, F, G, and
H.
* The S-Flag applies to Segment Types C, D, E, F, G, H, I, J, and K.
The value of the S-Flag MUST be ignored for Segment Types A and B.
* The B-Flag applies to Segment Types B, I, J, and K. The value of
the B-Flag MUST be ignored for Segment Types A, C, D, E, F, G, and
H.
3. IANA Considerations
3.1. SR Policy Segment List Sub-TLVs
IANA has allocated the following code points from the "SR Policy
Segment List Sub-TLVs" registry [RFC 9830] under the "Border Gateway
Protocol (BGP) Tunnel Encapsulation" registry group.
+=======+========================+===========+
| Value | Description | Reference |
+=======+========================+===========+
| 3 | Type C Segment sub-TLV | RFC 9831 |
+-------+------------------------+-----------+
| 4 | Type D Segment sub-TLV | RFC 9831 |
+-------+------------------------+-----------+
| 5 | Type E Segment sub-TLV | RFC 9831 |
+-------+------------------------+-----------+
| 6 | Type F Segment sub-TLV | RFC 9831 |
+-------+------------------------+-----------+
| 7 | Type G Segment sub-TLV | RFC 9831 |
+-------+------------------------+-----------+
| 8 | Type H Segment sub-TLV | RFC 9831 |
+-------+------------------------+-----------+
| 14 | Type I Segment sub-TLV | RFC 9831 |
+-------+------------------------+-----------+
| 15 | Type J Segment sub-TLV | RFC 9831 |
+-------+------------------------+-----------+
| 16 | Type K Segment sub-TLV | RFC 9831 |
+-------+------------------------+-----------+
Table 1: SR Policy Segment List Code Points
3.2. SR Policy Segment Flags
IANA has allocated code points from the "SR Policy Segment Flags"
registry [RFC 9830] under the "Border Gateway Protocol (BGP) Tunnel
Encapsulation" registry group.
+=====+=============================+===========+
| Bit | Description | Reference |
+=====+=============================+===========+
| 1 | SR Algorithm Flag (A-Flag) | RFC 9831 |
+-----+-----------------------------+-----------+
| 2 | SID Specified Flag (S-Flag) | RFC 9831 |
+-----+-----------------------------+-----------+
Table 2: SR Policy Segment Flags
4. Security Considerations
The security considerations in [RFC 9830] apply to the Segment Types
defined in this document. No additional security considerations are
introduced.
5. Manageability Considerations
The operations and manageability considerations in [RFC 9830] apply to
the Segment Types defined in this document. No additional operations
and manageability considerations are introduced.
6. Normative References
[RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC 2119, March 1997,
<https://www.rfc-editor.org/info/RFC 2119>.
[RFC 8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC 8174,
May 2017, <https://www.rfc-editor.org/info/RFC 8174>.
[RFC 8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing Architecture", RFC 8402, DOI 10.17487/RFC 8402,
July 2018, <https://www.rfc-editor.org/info/RFC 8402>.
[RFC 8660] Bashandy, A., Ed., Filsfils, C., Ed., Previdi, S.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing with the MPLS Data Plane", RFC 8660,
DOI 10.17487/RFC 8660, December 2019,
<https://www.rfc-editor.org/info/RFC 8660>.
[RFC 8754] 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/RFC 8754, March 2020,
<https://www.rfc-editor.org/info/RFC 8754>.
[RFC 8986] Filsfils, C., Ed., Camarillo, P., Ed., Leddy, J., Voyer,
D., Matsushima, S., and Z. Li, "Segment Routing over IPv6
(SRv6) Network Programming", RFC 8986,
DOI 10.17487/RFC 8986, February 2021,
<https://www.rfc-editor.org/info/RFC 8986>.
[RFC 9256] Filsfils, C., Talaulikar, K., Ed., Voyer, D., Bogdanov,
A., and P. Mattes, "Segment Routing Policy Architecture",
RFC 9256, DOI 10.17487/RFC 9256, July 2022,
<https://www.rfc-editor.org/info/RFC 9256>.
[RFC 9552] Talaulikar, K., Ed., "Distribution of Link-State and
Traffic Engineering Information Using BGP", RFC 9552,
DOI 10.17487/RFC 9552, December 2023,
<https://www.rfc-editor.org/info/RFC 9552>.
[RFC 9830] Previdi, S., Filsfils, C., Talaulikar, K., Ed., Mattes,
P., and D. Jain, "Advertising Segment Routing Policies in
BGP", RFC 9830, DOI 10.17487/RFC 9830, September 2025,
<https://www.rfc-editor.org/info/RFC 9830>.
Acknowledgments
The authors would like to Dan Romascanu, Stig Venaas, and Russ
Housley for their comments and review. The authors would like to
thank Susan Hares for her detailed shepherd review that helped in
improving the document.
Authors' Addresses
Ketan Talaulikar (editor)
Cisco Systems
India
Email: ketant.ietf@gmail.com
Clarence Filsfils
Cisco Systems
Brussels
Belgium
Email: cfilsfil@cisco.com
Stefano Previdi
Huawei Technologies
Italy
Email: stefano@previdi.net
Paul Mattes
Microsoft
One Microsoft Way
Redmond, WA 98052
United States of America
Email: pamattes@microsoft.com
Dhanendra Jain
Google
Email: dhanendra.ietf@gmail.com
RFC TOTAL SIZE: 33518 bytes
PUBLICATION DATE: Friday, September 12th, 2025
LEGAL RIGHTS: The IETF Trust (see BCP 78)
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