



Internet Engineering Task Force (IETF)                      M. Koldychev
Request for Comments: 9862                                  S. Sivabalan
Updates: 8231                                          Ciena Corporation
Category: Standards Track                                       S. Sidor
ISSN: 2070-1721                                      Cisco Systems, Inc.
                                                                C. Barth
                                                  Juniper Networks, Inc.
                                                                 S. Peng
                                                     Huawei Technologies
                                                              H. Bidgoli
                                                                   Nokia
                                                            October 2025


 Path Computation Element Communication Protocol (PCEP) Extensions for
              Segment Routing (SR) Policy Candidate Paths

Abstract

   A Segment Routing (SR) Policy is an ordered list of instructions
   called "segments" that represent a source-routed policy.  Packet
   flows are steered into an SR Policy on a node where it is
   instantiated.  An SR Policy is made of one or more Candidate Paths.

   This document specifies the Path Computation Element Communication
   Protocol (PCEP) extension to signal Candidate Paths of an SR Policy.
   Additionally, this document updates RFC 8231 to allow delegation and
   setup of an SR Label Switched Path (LSP) without using the path
   computation request and reply messages.  This document is applicable
   to both Segment Routing over MPLS (SR-MPLS) and Segment Routing over
   IPv6 (SRv6).

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/rfc9862.

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.  Terminology
   3.  Overview
   4.  SR Policy Association (SRPA)
     4.1.  SR Policy Identifier
     4.2.  SR Policy Candidate Path Identifier
     4.3.  SR Policy Candidate Path Attributes
     4.4.  Association Parameters
     4.5.  Association Information
       4.5.1.  SRPOLICY-POL-NAME TLV
       4.5.2.  SRPOLICY-CPATH-ID TLV
       4.5.3.  SRPOLICY-CPATH-NAME TLV
       4.5.4.  SRPOLICY-CPATH-PREFERENCE TLV
   5.  SR Policy Signaling Extensions
     5.1.  SRPOLICY-CAPABILITY TLV
     5.2.  LSP Object TLVs
       5.2.1.  COMPUTATION-PRIORITY TLV
       5.2.2.  EXPLICIT-NULL-LABEL-POLICY TLV
       5.2.3.  INVALIDATION TLV
         5.2.3.1.  Drop-Upon-Invalid Applies to SR Policy
     5.3.  Updates to RFC 8231
   6.  IANA Considerations
     6.1.  Association Type
     6.2.  PCEP TLV Type Indicators
     6.3.  PCEP Errors
     6.4.  TE-PATH-BINDING TLV Flag Field
     6.5.  SR Policy Invalidation Operational State
     6.6.  SR Policy Invalidation Configuration State
     6.7.  SR Policy Capability TLV Flag Field
   7.  Security Considerations
   8.  Manageability Considerations
     8.1.  Control of Function and Policy
     8.2.  Information and Data Models
     8.3.  Liveness Detection and Monitoring
     8.4.  Verify Correct Operations
     8.5.  Requirements on Other Protocols
     8.6.  Impact on Network Operations
   9.  References
     9.1.  Normative References
     9.2.  Informative References
   Acknowledgements
   Contributors
   Authors' Addresses

1.  Introduction

   "Segment Routing Policy Architecture" [RFC9256] details the concepts
   of Segment Routing (SR) Policy [RFC8402] and approaches to steering
   traffic into an SR Policy.

   "Path Computation Element Communication Protocol (PCEP) Extensions
   for Segment Routing" [RFC8664] specifies extensions to the PCEP that
   allow a stateful Path Computation Element (PCE) to compute and
   initiate Traffic Engineering (TE) paths, as well as a Path
   Computation Client (PCC) to request a path subject to certain
   constraints and optimization criteria in an SR domain.  Although PCEP
   extensions introduced in [RFC8664] enable the creation of SR-TE
   paths, these do not constitute SR Policies as defined in [RFC9256].
   Therefore, they lack support for:

   *  Association of SR Policy Candidate Paths signaled via PCEP with
      Candidate Paths of the same SR Policy signaled via other sources
      (e.g., local configuration or BGP).

   *  Association of an SR Policy with an intent via color, enabling
      headend-based steering of BGP service routes over SR Policies
      provisioned via PCEP.

   "Path Computation Element Communication Protocol (PCEP) Extensions
   for Establishing Relationships between Sets of Label Switched Paths
   (LSPs)" [RFC8697] introduces a generic mechanism to create a grouping
   of LSPs that is called an "Association".

   An SR Policy is associated with one or more Candidate Paths.  A
   Candidate Path is the unit for signaling an SR Policy to a headend as
   described in Section 2.2 of [RFC9256].  This document extends
   [RFC8664] to support signaling SR Policy Candidate Paths as LSPs and
   to signal Candidate Path membership in an SR Policy by means of the
   Association mechanism.  A PCEP Association corresponds to an SR
   Policy and an LSP corresponds to a Candidate Path.  The unit of
   signaling in PCEP is the LSP, thus, all the information related to an
   SR Policy is carried at the Candidate Path level.

   Also, this document updates Section 5.8.2 of [RFC8231], making the
   use of Path Computation Request (PCReq) and Path Computation Reply
   (PCRep) messages optional for LSPs that are set up using Path Setup
   Type 1 (for Segment Routing) [RFC8664] and Path Setup Type 3 (for
   SRv6) [RFC9603] with the aim of reducing the PCEP message exchanges
   and simplifying implementation.

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 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

2.  Terminology

   This document uses the following terms defined in [RFC5440]:

   *  Explicit Route Object (ERO)

   *  Path Computation Client (PCC)

   *  Path Computation Element (PCE)

   *  PCEP Peer

   *  PCEP speaker

   This document uses the following term defined in [RFC3031]:

   *  Label Switched Path (LSP)

   This document uses the following term defined in [RFC9552]:

   *  Border Gateway Protocol - Link State (BGP-LS)

   The following other terms are used in this document:

   Endpoint:  The IPv4 or IPv6 endpoint address of an SR Policy, as
      described in Section 2.1 of [RFC9256].

   Color:  The 32-bit color of an SR Policy, as described in Section 2.1
      of [RFC9256].

   Protocol-Origin:  The protocol that was used to create a Candidate
      Path, as described in Section 2.3 of [RFC9256].

   Originator:  A device that created a Candidate Path, as described in
      Section 2.4 of [RFC9256].

   Discriminator:  Distinguishes Candidate Paths created by the same
      device, as described in Section 2.5 of [RFC9256].

   Association parameters:  Refers to the key data that uniquely
      identifies an Association, as described in [RFC8697].

   Association information:  Refers to information related to
      Association Type, as described in Section 6.1.4 of [RFC8697].

   SR Policy LSP:  An LSP setup using Path Setup Type [RFC8408] 1 (for
      Segment Routing) or 3 (for SRv6).

   SR Policy Association (SRPA):  A new Association Type used to group
      Candidate Paths belonging to the same SR Policy.  Depending on the
      discussion context, it can refer to the PCEP ASSOCIATION object of
      an SR Policy type or to a group of LSPs that belong to the
      association.

   The base PCEP specification [RFC4655] originally defined the use of
   the PCE architecture for MPLS and GMPLS networks with LSPs
   instantiated using the RSVP-TE signaling protocol.  Over time,
   support for additional path setup types such as SRv6 has been
   introduced [RFC9603].  The term "LSP" is used extensively in PCEP
   specifications, and in the context of this document, refers to a
   Candidate Path within an SR Policy, which may be an SRv6 path (still
   represented using the LSP object as specified in [RFC8231]).

3.  Overview

   The SR Policy is represented by a new type of PCEP Association,
   called the SR Policy Association (SRPA) (see Section 4).  The SR
   Policy Candidate Paths of a specific SR Policy are the LSPs within
   the same SRPA.  The extensions in this document specify the encoding
   of a single segment list within an SR Policy Candidate Path.
   Encoding of multiple segment lists is outside the scope of this
   document and is specified in [PCEP-MULTIPATH].

   An SRPA carries three pieces of information: SR Policy Identifier, SR
   Policy Candidate Path Identifier, and SR Policy Candidate Path
   Attribute(s).

   This document also specifies some additional information that is not
   encoded as part of an SRPA: computation priority of the LSP, Explicit
   NULL Label Policy for the unlabeled IP packets and Drop-Upon-Invalid
   behavior for traffic steering when the LSP is operationally down (see
   Section 5).

4.  SR Policy Association (SRPA)

   Per [RFC8697], LSPs are associated with other LSPs with which they
   interact by adding them to a common association group.  An
   association group is uniquely identified by the combination of the
   following fields in the ASSOCIATION object (Section 6.1 of
   [RFC8697]): Association Type, Association ID, Association Source, and
   (if present) Global Association Source, or Extended Association ID.
   These fields are referred to as "association parameters"
   (Section 4.4).

   [RFC8697] specifies the ASSOCIATION object with two Object-Types for
   IPv4 and IPv6 that includes the field Association Type.  This
   document defines a new Association Type (6) "SR Policy Association"
   for an SRPA.

   [RFC8697] specifies the mechanism for the capability advertisement of
   the Association Types supported by a PCEP speaker by defining an
   ASSOC-Type-List TLV to be carried within an OPEN object.  This
   capability exchange for the SRPA Type MUST be done before using the
   SRPA.  To that aim, a PCEP speaker MUST include the SRPA Type (6) in
   the ASSOC-Type-List TLV and MUST receive the same from the PCEP peer
   before using the SRPA (Section 6.1).

   An SRPA MUST be assigned for all SR Policy LSPs by the PCEP speaker
   originating the LSP if the capability was advertised by both PCEP
   speakers.  If the above condition is not satisfied, then the
   receiving PCEP speaker MUST send a PCErr message with:

   *  Error-Type = 6 "Mandatory Object Missing"

   *  Error-value = 22 "Missing SR Policy Association"

   A given LSP MUST belong to one SRPA at most, since an SR Policy
   Candidate Path cannot belong to multiple SR Policies.  If a PCEP
   speaker receives a PCEP message requesting to join more than one SRPA
   for the same LSP, then the PCEP speaker MUST send a PCErr message
   with:

   *  Error-Type = 26 "Association Error"

   *  Error-value = 7 "Cannot join the association group"

   The existing behavior for the use of Binding SID (BSID) with an SR
   Policy is already documented in [RFC9604].  If BSID value allocation
   failed because of conflict with the BSID used by another policy, then
   the PCEP peer MUST send a PCErr message with:

   *  Error-Type = 32 "Binding label/SID failure"

   *  Error-value = 2 "Unable to allocate the specified binding value"

4.1.  SR Policy Identifier

   The SR Policy Identifier uniquely identifies an SR Policy [RFC9256]
   within the SR domain.  The SR Policy Identifier is assigned by the
   PCEP peer originating the LSP and MUST be uniform across all the PCEP
   sessions.  Candidate Paths within an SR Policy MUST carry the same SR
   Policy Identifiers in their SRPAs.  Candidate Paths within an SR
   Policy MUST NOT change their SR Policy Identifiers for the lifetime
   of the PCEP session.  If the above conditions are not satisfied, the
   receiving PCEP speaker MUST send a PCEP Error (PCErr) message with:

   *  Error-Type = 26 "Association Error"

   *  Error-value = 20 "SR Policy Identifier Mismatch"

   The SR Policy Identifier consists of:

   *  Headend router where the SR Policy originates.

   *  Color of the SR Policy ([RFC9256], Section 2.1).

   *  Endpoint of the SR Policy ([RFC9256], Section 2.1).

4.2.  SR Policy Candidate Path Identifier

   The SR Policy Candidate Path Identifier uniquely identifies the SR
   Policy Candidate Path within the context of an SR Policy.  The SR
   Policy Candidate Path Identifier is assigned by the PCEP peer
   originating the LSP.  Candidate Paths within an SR Policy MUST NOT
   change their SR Policy Candidate Path Identifiers for the lifetime of
   the PCEP session.  Two or more Candidate Paths within an SR Policy
   MUST NOT carry the same SR Policy Candidate Path Identifiers in their
   SRPAs.  If the above conditions are not satisfied, the PCEP speaker
   MUST send a PCErr message with:

   *  Error-Type = 26 "Association Error"

   *  Error-value = 21 "SR Policy Candidate Path Identifier Mismatch"

   The SR Policy Candidate Path Identifier consists of:

   *  Protocol-Origin ([RFC9256], Section 2.3)

   *  Originator ([RFC9256], Section 2.4)

   *  Discriminator ([RFC9256], Section 2.5)

4.3.  SR Policy Candidate Path Attributes

   SR Policy Candidate Path Attributes carry optional, non-key
   information about a Candidate Path and MAY change during the lifetime
   of an LSP.  SR Policy Candidate Path Attributes consist of:

   *  Candidate Path Preference ([RFC9256], Section 2.7)

   *  Candidate Path name ([RFC9256], Section 2.6)

   *  SR Policy name ([RFC9256], Section 2.1)

4.4.  Association Parameters

   Per Section 2.1 of [RFC9256], an SR Policy is identified through the
   <Headend, Color, Endpoint> tuple.

   The association parameters consist of:

   Association Type:  Set to 6 "SR Policy Association".

   Association Source (IPv4/IPv6):  Set to the headend value of the SR
      Policy, as defined in [RFC9256], Section 2.1.

   Association ID (16 bit):  Always set to the numeric value 1.

   Extended Association ID TLV:  Mandatory TLV for an SRPA.  Encodes the
      Color and Endpoint of the SR Policy (Figure 1).

       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            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                             Color                             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ~                           Endpoint                            ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                 Figure 1: Extended Association ID TLV Format

      Type:  31 for the Extended Association ID TLV [RFC8697].

      Length:  8 octets if IPv4 address or 20 octets if IPv6 address is
         encoded in the Endpoint field.

      Color:  Unsigned non-zero 32-bit integer value, SR Policy color
         per Section 2.1 of [RFC9256].

      Endpoint:  Can be either IPv4 (4 octets) or IPv6 address (16
         octets).  This value MAY be different from the one contained in
         the destination address field in the END-POINTS object, or in
         the Tunnel Endpoint Address field in the LSP-IDENTIFIERS TLV
         (Section 2.1 of [RFC9256]).

   If a PCEP speaker receives an SRPA object whose association
   parameters do not follow the above specification, then the PCEP
   speaker MUST send a PCErr message with:

   *  Error-Type = 26 "Association Error"

   *  Error-value = 20 "SR Policy Identifier Mismatch"

   The encoding choice of the association parameters in this way is
   meant to guarantee that there is no possibility of a race condition
   when multiple PCEP speakers want to associate the same SR Policy at
   the same time.  By adhering to this format, all PCEP speakers come up
   with the same association parameters independently of each other
   based on the SR Policy parameters [RFC9256].

   The last hop of a computed SR Policy Candidate Path MAY differ from
   the Endpoint contained in the <Headend, Color, Endpoint> tuple.  An
   example use case is to terminate the SR Policy before reaching the
   Endpoint and have decapsulated traffic be forwarded the rest of the
   path to the Endpoint node using the Interior Gateway Protocol (IGP)
   shortest path(s).  In this example, the destination of the SR Policy
   Candidate Paths will be some node before the Endpoint, but the
   Endpoint value is still used at the headend to steer traffic with
   that Endpoint IP address into the SR Policy.  The destination of the
   SR Policy Candidate Path is signaled using the END-POINTS object and/
   or the LSP-IDENTIFIERS TLV, per the usual PCEP procedure.  When
   neither the END-POINTS object nor the LSP-IDENTIFIERS TLV is present,
   the PCEP speaker MUST extract the destination from the Endpoint field
   in the SRPA Extended Association ID TLV.

   SR Policy with Color-Only steering is signaled with the Endpoint
   value set to unspecified, i.e., 0.0.0.0 for IPv4 or :: for IPv6, per
   Section 8.8 of [RFC9256].

4.5.  Association Information

   The SRPA object may carry the following TLVs:

   SRPOLICY-POL-NAME TLV (Section 4.5.1):  (optional) encodes the SR
      Policy Name string.

   SRPOLICY-CPATH-ID TLV (Section 4.5.2):  (mandatory) encodes the SR
      Policy Candidate Path Identifier.

   SRPOLICY-CPATH-NAME TLV (Section 4.5.3):  (optional) encodes the SR
      Policy Candidate Path string name.

   SRPOLICY-CPATH-PREFERENCE TLV (Section 4.5.4):  (optional) encodes
      the SR Policy Candidate Path Preference value.

   When a mandatory TLV is missing from an SRPA object, the PCEP speaker
   MUST send a PCErr message with:

   *  Error-Type = 6 "Mandatory Object Missing"

   *  Error-value = 21 "Missing SR Policy Mandatory TLV"

   Only one TLV instance of each TLV type can be carried in an SRPA
   object, and only the first occurrence is processed.  Any others MUST
   be silently ignored.

4.5.1.  SRPOLICY-POL-NAME TLV

   The SRPOLICY-POL-NAME TLV (Figure 2) is an optional TLV for the SRPA
   object.  It is RECOMMENDED that the size of the name for the SR
   Policy is limited to 255 bytes.  Implementations MAY choose to
   truncate long names to 255 bytes to simplify interoperability with
   other protocols.

       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            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      ~                       SR Policy Name                          ~
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                   Figure 2: SRPOLICY-POL-NAME TLV Format

   Type:  56 for the SRPOLICY-POL-NAME TLV.

   Length:  Indicates the length of the value portion of the TLV in
      octets and MUST be greater than 0.  The TLV MUST be zero-padded so
      that the TLV is 4-octet aligned.  Padding is not included in the
      Length field.

   SR Policy Name:  SR Policy name, as defined in Section 2.1 of
      [RFC9256].  It MUST be a string of printable ASCII [RFC0020]
      characters, without a NULL terminator.

4.5.2.  SRPOLICY-CPATH-ID TLV

   The SRPOLICY-CPATH-ID TLV (Figure 3) is a mandatory TLV for the SRPA
   object.

       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            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Proto-Origin |                 Reserved                      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         Originator ASN                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      |                       Originator Address                      |
      |                                                               |
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         Discriminator                         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                   Figure 3: SRPOLICY-CPATH-ID TLV Format

   Type:  57 for the SRPOLICY-CPATH-ID TLV.

   Length:  28.

   Protocol-Origin:  8-bit unsigned integer value that encodes the
      Protocol-Origin.  The values of this field are specified in the
      IANA registry "SR Policy Protocol Origin" under the "Segment
      Routing" registry group, which is introduced in Section 8.4 of
      [RFC9857].  Note that in the PCInitiate message [RFC8281], the
      Protocol-Origin is always set to 10 - "PCEP (In PCEP or when BGP-
      LS Producer is PCE)".  The "SR Policy Protocol Origin" IANA
      registry includes a combination of values intended for use in PCEP
      and BGP-LS.  When the registry contains two variants of values
      associated with the mechanism or protocol used for provisioning of
      the Candidate Path, for example 1 - "PCEP" and 10 - "PCEP (In PCEP
      or when BGP-LS Producer is PCE)", the "(In PCEP or when BGP-LS
      Producer is PCE)", then variants MUST be used in PCEP.

   Reserved:  This field MUST be set to zero on transmission and MUST be
      ignored on receipt.

   Originator Autonomous System Number (ASN):  Represented as a 32-bit
      unsigned integer value, part of the originator identifier, as
      specified in Section 2.4 of [RFC9256].  When sending a PCInitiate
      message [RFC8281], the PCE is the originator of the Candidate
      Path.  If the PCE is configured with an ASN, then it MUST set it;
      otherwise, the ASN is set to 0.

   Originator Address:  Represented as a 128-bit value as specified in
      Section 2.4 of [RFC9256].  When sending a PCInitiate message, the
      PCE is acting as the originator and therefore MAY set this to an
      address that it owns.

   Discriminator:  32-bit unsigned integer value that encodes the
      Discriminator of the Candidate Path, as specified in Section 2.5
      of [RFC9256].  This is the field that mainly distinguishes
      different SR Policy Candidate Paths, coming from the same
      originator.  It is allowed to be any number in the 32-bit range.

4.5.3.  SRPOLICY-CPATH-NAME TLV

   The SRPOLICY-CPATH-NAME TLV (Figure 4) is an optional TLV for the
   SRPA object.  It is RECOMMENDED that the size of the name for the SR
   Policy is limited to 255 bytes.  Implementations MAY choose to
   truncate long names to 255 bytes to simplify interoperability with
   other protocols.

       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            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      ~                 SR Policy Candidate Path Name                 ~
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                  Figure 4: SRPOLICY-CPATH-NAME TLV Format

   Type:  58 for the SRPOLICY-CPATH-NAME TLV.

   Length:  Indicates the length of the value portion of the TLV in
      octets and MUST be greater than 0.  The TLV MUST be zero-padded so
      that the TLV is 4-octet aligned.  Padding is not included in the
      Length field.

   SR Policy Candidate Path Name:  SR Policy Candidate Path Name, as
      defined in Section 2.6 of [RFC9256].  It MUST be a string of
      printable ASCII characters, without a NULL terminator.

4.5.4.  SRPOLICY-CPATH-PREFERENCE TLV

   The SRPOLICY-CPATH-PREFERENCE TLV (Figure 5) is an optional TLV for
   the SRPA object.  If the TLV is absent, then the default Preference
   value is 100, per Section 2.7 of [RFC9256].

       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            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                           Preference                          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

               Figure 5: SRPOLICY-CPATH-PREFERENCE TLV Format

   Type:  59 for the SRPOLICY-CPATH-PREFERENCE TLV.

   Length:  4.

   Preference:  32-bit unsigned integer value that encodes the
      Preference of the Candidate Path as defined in Section 2.7 of
      [RFC9256].

5.  SR Policy Signaling Extensions

   This section introduces mechanisms described for SR Policies in
   [RFC9256] to PCEP.  These extensions do not make use of the SRPA for
   signaling in PCEP; therefore, they cannot rely on the Association
   capability negotiation in the ASSOC-Type-List TLV.  Instead, separate
   capability negotiation is required.

   This document specifies four new TLVs to be carried in the OPEN or
   LSP object.  Only one TLV instance of each type can be carried, and
   only the first occurrence is processed.  Any others MUST be ignored.

5.1.  SRPOLICY-CAPABILITY TLV

   The SRPOLICY-CAPABILITY TLV (Figure 6) is a TLV for the OPEN object.
   It is used at session establishment to learn the peer's capabilities
   with respect to SR Policy.  Implementations that support SR Policy
   MUST include the SRPOLICY-CAPABILITY TLV in the OPEN object if the
   extension is enabled.  In addition, the ASSOC-Type-List TLV
   containing SRPA Type (6) MUST be present in the OPEN object, as
   specified in Section 4.

   If a PCEP speaker receives an SRPA but the SRPOLICY-CAPABILITY TLV is
   not exchanged, then the PCEP speaker MUST send a PCErr message with
   Error-Type = 10 "Reception of an invalid object" and Error-value = 44
   "Missing SRPOLICY-CAPABILITY TLV" and MUST then close the PCEP
   session.

       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                   |L| |I|E|P|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                  Figure 6: SRPOLICY-CAPABILITY TLV Format

   Type:  71 for the SRPOLICY-CAPABILITY TLV.

   Length:  4.

   Flags:  32 bits.  The following flags are currently defined:

      P-flag (Computation Priority):  If set to 1 by a PCEP speaker, the
         P-flag indicates that the PCEP speaker supports the handling of
         the COMPUTATION-PRIORITY TLV for the SR Policy (Section 5.2.1).
         If this flag is set to 0, then the receiving PCEP speaker MUST
         NOT send the COMPUTATION-PRIORITY TLV and MUST ignore it on
         receipt.

      E-flag (Explicit NULL Label Policy):  If set to 1 by a PCEP
         speaker, the E-flag indicates that the PCEP speaker supports
         the handling of the EXPLICIT-NULL-LABEL-POLICY TLV for the SR
         Policy (Section 5.2.2).  If this flag is set to 0, then the
         receiving PCEP speaker MUST NOT send the EXPLICIT-NULL-LABEL-
         POLICY TLV and MUST ignore it on receipt.

      I-flag (Invalidation):  If set to 1 by a PCEP speaker, the I-flag
         indicates that the PCEP speaker supports the handling of the
         INVALIDATION TLV for the SR Policy (Section 5.2.3).  If this
         flag is set to 0, then the receiving PCEP speaker MUST NOT send
         the INVALIDATION TLV and MUST ignore it on receipt.

      L-flag (Stateless Operation):  If set to 1 by a PCEP speaker, the
         L-flag indicates that the PCEP speaker supports the stateless
         (PCReq/PCRep) operations for the SR Policy (Section 5.3).  If
         the PCE set this flag to 0, then the PCC MUST NOT send PCReq
         messages to this PCE for the SR Policy.

   Unassigned bits MUST be set to 0 on transmission and MUST be ignored
   on receipt.  More flags can be assigned in the future per
   (Section 6.7).

5.2.  LSP Object TLVs

   This section is introducing three new TLVs to be carried in the LSP
   object introduced in Section 7.3 of [RFC8231].

5.2.1.  COMPUTATION-PRIORITY TLV

   The COMPUTATION-PRIORITY TLV (Figure 7) is an optional TLV.  It is
   used to signal the numerical computation priority, as specified in
   Section 2.12 of [RFC9256].  If the TLV is absent from the LSP object,
   and the P-flag in the SRPOLICY-CAPABILITY TLV is set to 1, a default
   Priority value of 128 is used.

       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            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |    Priority   |                   Reserved                    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                 Figure 7: COMPUTATION-PRIORITY TLV Format

   Type:  68 for the COMPUTATION-PRIORITY TLV.

   Length:  4.

   Priority:  8-bit unsigned integer value that encodes numerical
      priority with which this LSP is to be recomputed by the PCE upon
      topology change.  The lowest value is the highest priority.

   Reserved:  This field MUST be set to zero on transmission and MUST be
      ignored on receipt.

5.2.2.  EXPLICIT-NULL-LABEL-POLICY TLV

   To steer an unlabeled IP packet into an SR Policy for the MPLS data
   plane, it is necessary to push a label stack of one or more labels on
   that packet.  The EXPLICIT-NULL-LABEL-POLICY TLV is an optional TLV
   for the LSP object used to indicate whether an Explicit NULL label
   [RFC3032] must be pushed on an unlabeled IP packet before any other
   labels.  The contents of this TLV are used by the SR Policy manager
   as described in Section 4.1 of [RFC9256].  If an EXPLICIT-NULL-LABEL-
   POLICY TLV is not present, the decision of whether to push an
   Explicit NULL label on a given packet is a matter of local
   configuration.  Note that Explicit NULL is currently only defined for
   SR-MPLS and not for SRv6.  Therefore, the receiving PCEP speaker MUST
   ignore the presence of this TLV for SRv6 Policies.

       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            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |    ENLP       |                   Reserved                    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

              Figure 8: EXPLICIT-NULL-LABEL-POLICY TLV Format

   Type:  69 for the EXPLICIT-NULL-LABEL-POLICY TLV.

   Length:  4.

   ENLP:  Explicit NULL Label Policy. 8-bit unsigned integer value that
      indicates whether Explicit NULL labels are to be pushed on
      unlabeled IP packets that are being steered into a given SR
      Policy.  The values of this field are specified in the IANA
      registry "SR Policy ENLP Values" under the "Segment Routing"
      registry group, which was introduced in Section 6.10 of [RFC9830].

   Reserved:  This field MUST be set to zero on transmission and MUST be
      ignored on receipt.

   The ENLP unassigned values may be used for future extensions, and
   implementations MUST ignore the EXPLICIT-NULL-LABEL-POLICY TLV with
   unrecognized values.  The behavior signaled in this TLV MAY be
   overridden by local configuration by the network operator based on
   their deployment requirements.  Section 4.1 of [RFC9256] describes
   the behavior on the headend for the handling of the Explicit NULL
   label.

5.2.3.  INVALIDATION TLV

   The INVALIDATION TLV (Figure 9) is an optional TLV.  This TLV is used
   to control traffic steering into an LSP when the LSP is operationally
   down/invalid.  In the context of SR Policy, this TLV facilitates the
   Drop-Upon-Invalid behavior, specified in Section 8.2 of [RFC9256].
   Normally, if the LSP is down/invalid then it stops attracting
   traffic; traffic that would have been destined for that LSP is
   redirected somewhere else, such as via IGP or another LSP.  The Drop-
   Upon-Invalid behavior specifies that the LSP keeps attracting traffic
   and the traffic has to be dropped at the headend.  Such an LSP is
   said to be "in drop state".  While in the drop state, the LSP
   operational state is "UP", as indicated by the O-flag in the LSP
   object.  However, the ERO object MAY be empty if no valid path has
   been computed.

   The INVALIDATION TLV is used in both directions between PCEP peers:

   *  PCE -> PCC: The PCE specifies to the PCC whether to enable or
      disable Drop-Upon-Invalid (Config).

   *  PCC -> PCE: The PCC reports the current setting of the Drop-Upon-
      Invalid (Config) and also whether the LSP is currently in the drop
      state (Oper).

       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            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   Oper        |   Config      |            Reserved           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                     Figure 9: INVALIDATION TLV Format

   Type:  70 for the INVALIDATION TLV.

   Length:  4.

   Oper:  An 8-bit flag field that encodes the operational state of the
      LSP.  It MUST be set to 0 by the PCE when sending and MUST be
      ignored by the PCC upon receipt.  See Section 6.5 for IANA
      information.

                               0 1 2 3 4 5 6 7
                              +-+-+-+-+-+-+-+-+
                              |             |D|
                              +-+-+-+-+-+-+-+-+

              Figure 10: Oper State of Drop-Upon-Invalid Feature

      *    D: Dropping - the LSP is actively dropping traffic as a
           result of Drop-Upon-Invalid behavior being activated.

      *    The unassigned bits in the Flag octet MUST be set to zero
           upon transmission and MUST be ignored upon receipt.

   Config:  An 8-bit flag field that encodes the configuration of the
      LSP.  See Section 6.6 for IANA information.

                               0 1 2 3 4 5 6 7
                              +-+-+-+-+-+-+-+-+
                              |             |D|
                              +-+-+-+-+-+-+-+-+

             Figure 11: Config State of Drop-Upon-Invalid Feature

      *    D: Drop enabled - the Candidate Path has Drop-Upon-Invalid
           feature enabled.

      *    The unassigned bits in the Flag octet MUST be set to zero
           upon transmission and MUST be ignored upon receipt.

   Reserved:  This field MUST be set to zero on transmission and MUST be
      ignored on receipt.

5.2.3.1.  Drop-Upon-Invalid Applies to SR Policy

   The Drop-Upon-Invalid feature is somewhat special among the other SR
   Policy features in the way that it is enabled/disabled.  This feature
   is enabled only on the whole SR Policy, not on a particular Candidate
   Path of that SR Policy, i.e., when any Candidate Path has Drop-Upon-
   Invalid enabled, it means that the whole SR Policy has the feature
   enabled.  As stated in Section 8.1 of [RFC9256], an SR Policy is
   invalid when all its Candidate Paths are invalid.

   Once all the Candidate Paths of an SR Policy have become invalid,
   then the SR Policy checks whether any of the Candidate Paths have
   Drop-Upon-Invalid enabled.  If so, the SR Policy enters the drop
   state and "activates" the highest preference Candidate Path that has
   the Drop-Upon-Invalid enabled.  Note that only one Candidate Path
   needs to be reported to the PCE with the Dropping (D) flag set.

5.3.  Updates to RFC 8231

   Section 5.8.2 of [RFC8231] allows delegation of an LSP in
   operationally down state, but at the same time mandates the use of
   PCReq before sending PCRpt.  This document updates Section 5.8.2 of
   [RFC8231], by making that section of [RFC8231] not applicable to SR
   Policy LSPs.  Thus, when a PCC wants to delegate an SR Policy LSP, it
   MAY proceed directly to sending PCRpt, without first sending PCReq
   and waiting for PCRep.  This has the advantage of reducing the number
   of PCEP messages and simplifying the implementation.

   Furthermore, a PCEP speaker is not required to support PCReq/PCRep at
   all for SR Policies.  The PCEP speaker can indicate support for
   PCReq/PCRep via the L-flag in the SRPOLICY-CAPABILITY TLV (see
   Section 5.1).  When this flag is cleared, or when the SRPOLICY-
   CAPABILITY TLV is absent, the given peer MUST NOT be sent PCReq/PCRep
   messages for SR Policy LSPs.  Conversely, when this flag is set, the
   peer can receive and process PCReq/PCRep messages for SR Policy LSPs.

   The above applies only to SR Policy LSPs and does not affect other
   LSP types, such as RSVP-TE LSPs.  For other LSP types, Section 5.8.2
   of [RFC8231] continues to apply.

6.  IANA Considerations

   IANA maintains the "Path Computation Element Protocol (PCEP) Numbers"
   registry at <https://www.iana.org/assignments/pcep>.

6.1.  Association Type

   This document defines a new Association Type: SR Policy Association.
   IANA has made the following assignment in the "ASSOCIATION Type
   Field" registry within the "Path Computation Element Protocol (PCEP)
   Numbers" registry group:

               +======+=======================+===========+
               | Type | Name                  | Reference |
               +======+=======================+===========+
               | 6    | SR Policy Association | RFC 9862  |
               +------+-----------------------+-----------+

                                 Table 1

6.2.  PCEP TLV Type Indicators

   This document defines eight new TLVs for carrying additional
   information about SR Policy and SR Policy Candidate Paths.  IANA has
   made the following assignments in the existing "PCEP TLV Type
   Indicators" registry:

            +=======+============================+===========+
            | Value | Description                | Reference |
            +=======+============================+===========+
            | 56    | SRPOLICY-POL-NAME          | RFC 9862  |
            +-------+----------------------------+-----------+
            | 57    | SRPOLICY-CPATH-ID          | RFC 9862  |
            +-------+----------------------------+-----------+
            | 58    | SRPOLICY-CPATH-NAME        | RFC 9862  |
            +-------+----------------------------+-----------+
            | 59    | SRPOLICY-CPATH-PREFERENCE  | RFC 9862  |
            +-------+----------------------------+-----------+
            | 68    | COMPUTATION-PRIORITY       | RFC 9862  |
            +-------+----------------------------+-----------+
            | 69    | EXPLICIT-NULL-LABEL-POLICY | RFC 9862  |
            +-------+----------------------------+-----------+
            | 70    | INVALIDATION               | RFC 9862  |
            +-------+----------------------------+-----------+
            | 71    | SRPOLICY-CAPABILITY        | RFC 9862  |
            +-------+----------------------------+-----------+

                                 Table 2

6.3.  PCEP Errors

   This document defines the following:

   *  one new Error-value within the "Mandatory Object Missing" Error-
      Type,

   *  one new Error-value within the "Reception of an invalid object",
      and

   *  two new Error-values within the "Association Error" Error-Type.

   IANA has made the following assignments in the "PCEP-ERROR Object
   Error Types and Values" registry of the "Path Computation Element
   Protocol (PCEP) Numbers" registry group.

   +============+=================+=======================+===========+
   | Error-Type | Meaning         | Error-value           | Reference |
   +============+=================+=======================+===========+
   | 6          | Mandatory       |                       | [RFC5440] |
   |            | Object Missing  |                       |           |
   |            +-----------------+-----------------------+-----------+
   |            |                 | 21: Missing SR Policy | RFC 9862  |
   |            |                 | Mandatory TLV         |           |
   |            +-----------------+-----------------------+-----------+
   |            |                 | 22: Missing SR Policy | RFC 9862  |
   |            |                 | Association           |           |
   +------------+-----------------+-----------------------+-----------+
   | 10         | Reception of an |                       | [RFC5440] |
   |            | invalid object  |                       |           |
   |            +-----------------+-----------------------+-----------+
   |            |                 | 44: Missing SRPOLICY- | RFC 9862  |
   |            |                 | CAPABILITY TLV        |           |
   +------------+-----------------+-----------------------+-----------+
   | 26         | Association     |                       | [RFC8697] |
   |            | Error           |                       |           |
   |            +-----------------+-----------------------+-----------+
   |            |                 | 20: SR Policy         | RFC 9862  |
   |            |                 | Identifiers Mismatch  |           |
   |            +-----------------+-----------------------+-----------+
   |            |                 | 21: SR Policy         | RFC 9862  |
   |            |                 | Candidate Path        |           |
   |            |                 | Identifier Mismatch   |           |
   +------------+-----------------+-----------------------+-----------+

                                 Table 3

6.4.  TE-PATH-BINDING TLV Flag Field

   A draft version of this document added a new bit in the "TE-PATH-
   BINDING TLV Flag Field" registry of the "Path Computation Element
   Protocol (PCEP) Numbers" registry group, which was early allocated by
   IANA.

   IANA has marked the bit position as deprecated.

          +=====+==================================+===========+
          | Bit | Description                      | Reference |
          +=====+==================================+===========+
          | 1   | Deprecated (Specified-BSID-only) | RFC 9862  |
          +-----+----------------------------------+-----------+

                                 Table 4

6.5.  SR Policy Invalidation Operational State

   IANA has created and now maintains a new registry under the "Path
   Computation Element Protocol (PCEP) Numbers" registry group.  The new
   registry is called "SR Policy Invalidation Operational Flags".  New
   values are to be assigned by "IETF Review" [RFC8126].  Each bit will
   be tracked with the following qualities:

   *  Bit (counting from bit 0 as the most significant bit)

   *  Description

   *  Reference

       +=====+========================================+===========+
       | Bit | Description                            | Reference |
       +=====+========================================+===========+
       | 0 - | Unassigned                             |           |
       | 6   |                                        |           |
       +-----+----------------------------------------+-----------+
       | 7   | D: Dropping - the LSP is actively      | RFC 9862  |
       |     | dropping traffic as a result of Drop-  |           |
       |     | Upon-Invalid behavior being activated. |           |
       +-----+----------------------------------------+-----------+

                                 Table 5

6.6.  SR Policy Invalidation Configuration State

   IANA has created and now maintains a new registry under the "Path
   Computation Element Protocol (PCEP) Numbers" registry group.  The new
   registry is called "SR Policy Invalidation Configuration Flags".  New
   values are to be assigned by "IETF Review" [RFC8126].  Each bit will
   be tracked with the following qualities:

   *  Bit (counting from bit 0 as the most significant bit)

   *  Description

   *  Reference

      +=======+========================================+===========+
      | Bit   | Description                            | Reference |
      +=======+========================================+===========+
      | 0 - 6 | Unassigned                             |           |
      +-------+----------------------------------------+-----------+
      | 7     | D: Drop enabled - the Candidate Path   | RFC 9862  |
      |       | has Drop-Upon-Invalid feature enabled. |           |
      +-------+----------------------------------------+-----------+

                                 Table 6

6.7.  SR Policy Capability TLV Flag Field

   IANA has created and now maintains a new registry under the "Path
   Computation Element Protocol (PCEP) Numbers" registry group.  The new
   registry is called "SR Policy Capability TLV Flag Field".  New values
   are to be assigned by "IETF Review" [RFC8126].  Each bit will be
   tracked with the following qualities:

   *  Bit (counting from bit 0 as the most significant bit)

   *  Description

   *  Reference

       +========+=====================================+===========+
       | Bit    | Description                         | Reference |
       +========+=====================================+===========+
       | 0 - 26 | Unassigned                          | RFC 9862  |
       +--------+-------------------------------------+-----------+
       | 27     | Stateless Operation (L-flag)        | RFC 9862  |
       +--------+-------------------------------------+-----------+
       | 28     | Unassigned                          | RFC 9862  |
       +--------+-------------------------------------+-----------+
       | 29     | Invalidation (I-flag)               | RFC 9862  |
       +--------+-------------------------------------+-----------+
       | 30     | Explicit NULL Label Policy (E-flag) | RFC 9862  |
       +--------+-------------------------------------+-----------+
       | 31     | Computation Priority (P-flag)       | RFC 9862  |
       +--------+-------------------------------------+-----------+

                                 Table 7

7.  Security Considerations

   The information carried in the newly defined SRPA object and TLVs
   could provide an eavesdropper with additional information about the
   SR Policy.

   The security considerations described in [RFC5440], [RFC8231],
   [RFC8281], [RFC8664], [RFC8697], [RFC9256], and [RFC9603] are
   applicable to this specification.

   As per [RFC8231], it is RECOMMENDED that these PCEP extensions can
   only be activated on authenticated and encrypted sessions across PCEs
   and PCCs belonging to the same administrative authority, using
   Transport Layer Security (TLS) [RFC8253] as per the recommendations
   and best current practices in [RFC9325].

8.  Manageability Considerations

   All manageability requirements and considerations listed in
   [RFC5440], [RFC8231], [RFC8664], [RFC9256], and [RFC9603] apply to
   PCEP protocol extensions defined in this document.  In addition,
   requirements and considerations listed in this section apply.

8.1.  Control of Function and Policy

   A PCE or PCC implementation MAY allow the capabilities specified in
   Section 5.1 and the capability for support of an SRPA advertised in
   the ASSOC-Type-List TLV to be enabled and disabled.

8.2.  Information and Data Models

   [PCEP-SRv6-YANG] defines a YANG module with common building blocks
   for PCEP extensions described in Section 4 of this document.

8.3.  Liveness Detection and Monitoring

   Mechanisms defined in this document do not imply any new liveness
   detection and monitoring requirements in addition to those already
   listed in [RFC5440], [RFC8664], and [RFC9256].

8.4.  Verify Correct Operations

   Operation verification requirements already listed in [RFC5440],
   [RFC8231], [RFC8664], [RFC9256], and [RFC9603] are applicable to
   mechanisms defined in this document.

   An implementation MUST allow the operator to view SR Policy
   Identifier and SR Policy Candidate Path Identifier advertised in an
   SRPA object.

   An implementation SHOULD allow the operator to view the capabilities
   defined in this document advertised by each PCEP peer.

   An implementation SHOULD allow the operator to view LSPs associated
   with a specific SR Policy Identifier.

8.5.  Requirements on Other Protocols

   The PCEP extensions defined in this document do not imply any new
   requirements on other protocols.

8.6.  Impact on Network Operations

   The mechanisms defined in [RFC5440], [RFC8231], [RFC9256], and
   [RFC9603] also apply to the PCEP extensions defined in this document.

9.  References

9.1.  Normative References

   [RFC0020]  Cerf, V., "ASCII format for network interchange", STD 80,
              RFC 20, DOI 10.17487/RFC0020, October 1969,
              <https://www.rfc-editor.org/info/rfc20>.

   [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>.

   [RFC3032]  Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y.,
              Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack
              Encoding", RFC 3032, DOI 10.17487/RFC3032, January 2001,
              <https://www.rfc-editor.org/info/rfc3032>.

   [RFC5440]  Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
              Element (PCE) Communication Protocol (PCEP)", RFC 5440,
              DOI 10.17487/RFC5440, March 2009,
              <https://www.rfc-editor.org/info/rfc5440>.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

   [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>.

   [RFC8231]  Crabbe, E., Minei, I., Medved, J., and R. Varga, "Path
              Computation Element Communication Protocol (PCEP)
              Extensions for Stateful PCE", RFC 8231,
              DOI 10.17487/RFC8231, September 2017,
              <https://www.rfc-editor.org/info/rfc8231>.

   [RFC8253]  Lopez, D., Gonzalez de Dios, O., Wu, Q., and D. Dhody,
              "PCEPS: Usage of TLS to Provide a Secure Transport for the
              Path Computation Element Communication Protocol (PCEP)",
              RFC 8253, DOI 10.17487/RFC8253, October 2017,
              <https://www.rfc-editor.org/info/rfc8253>.

   [RFC8281]  Crabbe, E., Minei, I., Sivabalan, S., and R. Varga, "Path
              Computation Element Communication Protocol (PCEP)
              Extensions for PCE-Initiated LSP Setup in a Stateful PCE
              Model", RFC 8281, DOI 10.17487/RFC8281, December 2017,
              <https://www.rfc-editor.org/info/rfc8281>.

   [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>.

   [RFC8408]  Sivabalan, S., Tantsura, J., Minei, I., Varga, R., and J.
              Hardwick, "Conveying Path Setup Type in PCE Communication
              Protocol (PCEP) Messages", RFC 8408, DOI 10.17487/RFC8408,
              July 2018, <https://www.rfc-editor.org/info/rfc8408>.

   [RFC8664]  Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W.,
              and J. Hardwick, "Path Computation Element Communication
              Protocol (PCEP) Extensions for Segment Routing", RFC 8664,
              DOI 10.17487/RFC8664, December 2019,
              <https://www.rfc-editor.org/info/rfc8664>.

   [RFC8697]  Minei, I., Crabbe, E., Sivabalan, S., Ananthakrishnan, H.,
              Dhody, D., and Y. Tanaka, "Path Computation Element
              Communication Protocol (PCEP) Extensions for Establishing
              Relationships between Sets of Label Switched Paths
              (LSPs)", RFC 8697, DOI 10.17487/RFC8697, January 2020,
              <https://www.rfc-editor.org/info/rfc8697>.

   [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>.

   [RFC9325]  Sheffer, Y., Saint-Andre, P., and T. Fossati,
              "Recommendations for Secure Use of Transport Layer
              Security (TLS) and Datagram Transport Layer Security
              (DTLS)", BCP 195, RFC 9325, DOI 10.17487/RFC9325, November
              2022, <https://www.rfc-editor.org/info/rfc9325>.

   [RFC9603]  Li, C., Ed., Kaladharan, P., Sivabalan, S., Koldychev, M.,
              and Y. Zhu, "Path Computation Element Communication
              Protocol (PCEP) Extensions for IPv6 Segment Routing",
              RFC 9603, DOI 10.17487/RFC9603, July 2024,
              <https://www.rfc-editor.org/info/rfc9603>.

9.2.  Informative References

   [PCEP-MULTIPATH]
              Koldychev, M., Sivabalan, S., Saad, T., Beeram, V. P.,
              Bidgoli, H., Yadav, B., Peng, S., Mishra, G. S., and S.
              Sidor, "Path Computation Element Communication Protocol
              (PCEP) Extensions for Signaling Multipath Information",
              Work in Progress, Internet-Draft, draft-ietf-pce-
              multipath-16, 17 October 2025,
              <https://datatracker.ietf.org/doc/html/draft-ietf-pce-
              multipath-16>.

   [PCEP-SRv6-YANG]
              Li, C., Sivabalan, S., Peng, S., Koldychev, M., and L.
              Ndifor, "A YANG Data Model for Segment Routing (SR) Policy
              and SR in IPv6 (SRv6) support in Path Computation Element
              Communications Protocol (PCEP)", Work in Progress,
              Internet-Draft, draft-ietf-pce-pcep-srv6-yang-08, 14
              October 2025, <https://datatracker.ietf.org/doc/html/
              draft-ietf-pce-pcep-srv6-yang-08>.

   [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>.

   [RFC4655]  Farrel, A., Vasseur, J.-P., and J. Ash, "A Path
              Computation Element (PCE)-Based Architecture", RFC 4655,
              DOI 10.17487/RFC4655, August 2006,
              <https://www.rfc-editor.org/info/rfc4655>.

   [RFC9552]  Talaulikar, K., Ed., "Distribution of Link-State and
              Traffic Engineering Information Using BGP", RFC 9552,
              DOI 10.17487/RFC9552, December 2023,
              <https://www.rfc-editor.org/info/rfc9552>.

   [RFC9604]  Sivabalan, S., Filsfils, C., Tantsura, J., Previdi, S.,
              and C. Li, Ed., "Carrying Binding Label/SID in PCE-Based
              Networks", RFC 9604, DOI 10.17487/RFC9604, August 2024,
              <https://www.rfc-editor.org/info/rfc9604>.

   [RFC9830]  Previdi, S., Filsfils, C., Talaulikar, K., Ed., Mattes,
              P., and D. Jain, "Advertising Segment Routing Policies in
              BGP", RFC 9830, DOI 10.17487/RFC9830, September 2025,
              <https://www.rfc-editor.org/info/rfc9830>.

   [RFC9857]  Previdi, S., Talaulikar, K., Ed., Dong, J., Gredler, H.,
              and J. Tantsura, "Advertisement of Segment Routing
              Policies Using BGP - Link State", RFC 9857, October 2025,
              <https://www.rfc-editor.org/info/rfc9857>.

Acknowledgements

   We would like to thank Abdul Rehman, Andrew Stone, Boris Khasanov,
   Cheng Li, Dhruv Dhody, Gorry Fairhurst, Gyan Mishra, Huaimo Chen,
   Ines Robles, Joseph Salowey, Ketan Talaulikar, Marina Fizgeer, Mike
   Bishopm, Praveen Kumar, Robert Sparks, Roman Danyliw, Stephane
   Litkowski, Tom Petch, Zoey Rose, Xiao Min, and Xiong Quan for their
   reviews and suggestions.

Contributors

   Dhruv Dhody
   Huawei
   India
   Email: dhruv.ietf@gmail.com


   Cheng Li
   Huawei Technologies
   Huawei Campus, No. 156 Beiqing Rd.
   Beijing
   10095
   China
   Email: chengli13@huawei.com


   Zafar Ali
   Cisco Systems, Inc
   Email: zali@cisco.com


   Rajesh Melarcode
   Cisco Systems, Inc.
   2000 Innovation Dr.
   Kanata Ontario
   Canada
   Email: rmelarco@cisco.com


Authors' Addresses

   Mike Koldychev
   Ciena Corporation
   385 Terry Fox Dr.
   Kanata Ontario K2K 0L1
   Canada
   Email: mkoldych@proton.me


   Siva Sivabalan
   Ciena Corporation
   385 Terry Fox Dr.
   Kanata Ontario K2K 0L1
   Canada
   Email: ssivabal@ciena.com


   Samuel Sidor
   Cisco Systems, Inc.
   Eurovea Central 3.
   811 09 Bratislava
   Slovakia
   Email: ssidor@cisco.com


   Colby Barth
   Juniper Networks, Inc.
   Email: cbarth@juniper.net


   Shuping Peng
   Huawei Technologies
   Huawei Campus, No. 156 Beiqing Rd.
   Beijing
   100095
   China
   Email: pengshuping@huawei.com


   Hooman Bidgoli
   Nokia
   Email: hooman.bidgoli@nokia.com
