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Path Computation Element Communication Protocol (PCEP) Extensions for Segment Routing (SR) Policy Candidate Paths
draft-ietf-pce-segment-routing-policy-cp-15

Document Type Active Internet-Draft (pce WG)
Authors Mike Koldychev , Siva Sivabalan , Colby Barth , Shuping Peng , Hooman Bidgoli
Last updated 2024-03-17
Replaces draft-barth-pce-segment-routing-policy-cp
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Submit PCEP extensions for SR Policy as Proposed Standard
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draft-ietf-pce-segment-routing-policy-cp-15
PCE Working Group                                           M. Koldychev
Internet-Draft                                              S. Sivabalan
Updates: 8231 (if approved)                            Ciena Corporation
Intended status: Standards Track                                C. Barth
Expires: 18 September 2024                        Juniper Networks, Inc.
                                                                 S. Peng
                                                     Huawei Technologies
                                                              H. Bidgoli
                                                                   Nokia
                                                           17 March 2024

 Path Computation Element Communication Protocol (PCEP) Extensions for
              Segment Routing (SR) Policy Candidate Paths
              draft-ietf-pce-segment-routing-policy-cp-15

Abstract

   Segment Routing (SR) allows a node to steer a packet flow along any
   path.  SR Policy is an ordered list of segments (i.e., instructions)
   that represent a source-routed policy.  Packet flows are steered into
   an SR Policy on a node where it is instantiated called a headend
   node.  An SR Policy is made of one or more candidate paths.

   This document specifies Path Computation Element Communication
   Protocol (PCEP) extension to associate candidate paths of the SR
   Policy.  Additionally, this document updates [RFC8231] to allow
   stateful bringup of an SR LSP, without using PCReq/PCRep messages.
   This document is applicable to both Segment Routing over MPLS and to
   Segment Routing over IPv6 (SRv6).

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.

Status of This Memo

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

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

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   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 18 September 2024.

Copyright Notice

   Copyright (c) 2024 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  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Overview  . . . . . . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  SR Policy Identifier  . . . . . . . . . . . . . . . . . .   5
     3.2.  SR Policy Candidate Path Identifier . . . . . . . . . . .   5
     3.3.  SR Policy Candidate Path Attributes . . . . . . . . . . .   5
   4.  SR Policy Association . . . . . . . . . . . . . . . . . . . .   6
     4.1.  Association Parameters  . . . . . . . . . . . . . . . . .   6
     4.2.  Association Information . . . . . . . . . . . . . . . . .   8
       4.2.1.  SR Policy Name TLV  . . . . . . . . . . . . . . . . .   8
       4.2.2.  SR Policy Candidate Path Identifier TLV . . . . . . .   9
       4.2.3.  SR Policy Candidate Path Name TLV . . . . . . . . . .  10
       4.2.4.  SR Policy Candidate Path Preference TLV . . . . . . .  11
   5.  Other Mechanisms  . . . . . . . . . . . . . . . . . . . . . .  11
     5.1.  SR Policy Capability TLV  . . . . . . . . . . . . . . . .  11
     5.2.  Computation Priority TLV  . . . . . . . . . . . . . . . .  13
     5.3.  Explicit Null Label Policy (ENLP) TLV . . . . . . . . . .  13
     5.4.  Invalidation TLV  . . . . . . . . . . . . . . . . . . . .  14
       5.4.1.  Drop-upon-invalid applies to SR Policy  . . . . . . .  15
     5.5.  Specified-BSID-only . . . . . . . . . . . . . . . . . . .  16
     5.6.  Stateless Operation . . . . . . . . . . . . . . . . . . .  16
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  17
     6.1.  Association Type  . . . . . . . . . . . . . . . . . . . .  17
     6.2.  PCEP TLV Type Indicators  . . . . . . . . . . . . . . . .  17
     6.3.  PCEP Errors . . . . . . . . . . . . . . . . . . . . . . .  18

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     6.4.  TE-PATH-BINDING TLV Flag field  . . . . . . . . . . . . .  18
     6.5.  SR Policy Candidate Path Protocol Origin field  . . . . .  18
     6.6.  SR Policy Explicit Null Label Policy field  . . . . . . .  19
   7.  Implementation Status . . . . . . . . . . . . . . . . . . . .  20
     7.1.  Cisco . . . . . . . . . . . . . . . . . . . . . . . . . .  21
     7.2.  Juniper . . . . . . . . . . . . . . . . . . . . . . . . .  21
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  21
   9.  Acknowledgement . . . . . . . . . . . . . . . . . . . . . . .  21
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  21
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  21
     10.2.  Informative References . . . . . . . . . . . . . . . . .  23
   Appendix A.  Contributors . . . . . . . . . . . . . . . . . . . .  23
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  24

1.  Introduction

   [RFC8664] specifies extensions that allow PCEP to work with basic SR-
   TE paths.  [RFC8697] introduces a generic mechanism to create a
   grouping of LSPs, called an Association.  [RFC9256] introduces the SR
   Policy construct as a grouping of SR Candidate Paths.

   This document extends [RFC8664] to support signaling SR Policy
   Candidate Paths and their attributes.  SR Policy is modeled in PCEP
   as an Association, where the SR Candidate Paths are the members of
   that Association.  Thus the PCE can take computation and control
   decisions about the Candidate Paths, with the additional knowledge
   that these Candidate Paths belong to the same SR Policy.

   Segment Routing Policy for Traffic Engineering [RFC9256] details the
   concepts of SR Policy and approaches to steering traffic into an SR
   Policy.

   PCEP Extensions for Segment Routing [RFC8664] specifies extensions to
   the Path Computation Element Protocol (PCEP) that allow a stateful
   PCE to compute and initiate Traffic Engineering (TE) paths, as well
   as a PCC to request a path subject to certain constraint(s) and
   optimization criteria in SR networks.

   PCEP Extensions for Establishing Relationships Between Sets of LSPs
   [RFC8697] introduces a generic mechanism to create a grouping of LSPs
   which can then be used to define associations between a set of LSPs
   and a set of attributes (such as configuration parameters or
   behaviors) and is equally applicable to stateful PCE (active and
   passive modes) and stateless PCE.

   This document extends [RFC8664] to support signaling SR Policy
   Candidate Paths and their attributes.  SR Policy is modeled in PCEP
   as an Association, where the SR Candidate Paths are the members of

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   that Association.  Thus the PCE can take computation and control
   decisions about the Candidate Paths, with the additional knowledge
   that these Candidate Paths belong to the same SR Policy.  This is
   accomplished via the use of the PCEP Association object with a new
   association type and several new TLVs.

2.  Terminology

   The following terminologies are used in this document:

   Endpoint:  The IPv4 or IPv6 endpoint address of the SR Policy in
      question, as described in [RFC9256].

   SRPA:  SR Policy Association.  A new association type 'SR Policy
      Association' is used to group candidate paths belonging to the SR
      Policy.  Depending on discussion context, it can refer to the PCEP
      ASSOCIATION object of SR Policy type or to a group of LSPs that
      belong to the association.

   Association Parameters:  As described in [RFC8697], refers to the key
      data, that uniquely identifies the Association.

   Association Information:  As described in [RFC8697], refers to the
      non-key information about the Association.

3.  Overview

   The SR Policy is represented by a new type of PCEP Association,
   called the SR Policy Association (SRPA).  The SR Candidate Paths of
   an SR Policy are the PCEP LSPs within the same SRPA.  The subject of
   encoding multiple Segment Lists within an SR Policy Candidate Path is
   described in [I-D.ietf-pce-multipath].

   The 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 SRPA: Computation Priority, Explicit Null Label
   Policy, Drop-upon-invalid behavior, and Specified-BSID-only.

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3.1.  SR Policy Identifier

   SR Policy Identifier uniquely identifies the SR Policy [RFC9256]
   within the network.  SR Policy Identifier MUST be the same for all SR
   Policy Candidate Paths in the same SRPA.  SR Policy Identifier MUST
   NOT change for a given SR Policy Candidate Path during its lifetime.
   SR Policy Identifier MUST be different for different SRPAs.  When
   these rules are not satisfied, the PCEP speaker MUST send a PCErr
   message with Error-Type = 26 "Association Error", Error Value = 20
   "SR Policy Identifier Mismatch".  SR Policy Identifier consist of:

   *  Headend router where the SR Policy originates.

   *  Color of SR Policy.

   *  Endpoint of SR Policy.

3.2.  SR Policy Candidate Path Identifier

   SR Policy Candidate Path Identifier uniquely identifies the SR Policy
   Candidate Path within the context of an SR Policy.  SR Policy
   Candidate Path Identifier MUST NOT change for a given LSP during its
   lifetime.  SR Policy Candidate Path Identifier MUST be different for
   distinct Candidate Paths within the same SRPA.  When these rules 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".  SR Policy Candidate Path Identifier
   consist of:

   *  Protocol Origin.

   *  Originator.

   *  Discriminator.

3.3.  SR Policy Candidate Path Attributes

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

   *  Preference.

   *  Optionally, the SR Policy Candidate Path name.

   *  Optionally, the SR Policy name.

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4.  SR Policy Association

   As per [RFC8697], LSPs are associated with other LSPs with which they
   interact by adding them to a common association group.  As described
   in [RFC8697], the association group is uniquely identified by the
   combination of the following fields in the ASSOCIATION object:
   Association Type, Association ID, Association Source, and (if
   present) Global Association Source or Extended Association ID,
   referred to as Association Parameters.

   [RFC8697] specify the ASSOCIATION Object with two Object-Types for
   IPv4 and IPv6 which includes the field "Association Type".  This
   document defines a new Association type (6) "SR Policy Association"
   for 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 SR Policy Association Types MUST be done
   before using the SRPA.  Thus, the 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 SRPA.

   A given LSP MUST belong to at most one SRPA, 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".

4.1.  Association Parameters

   As per [RFC9256], an SR Policy is identified through the tuple
   <headend, color, endpoint>.  The headend is encoded in the
   'Association Source' field in the ASSOCIATION object and the color
   and endpoint are encoded as part of the Extended Association ID TLV.

   The Association Parameters (see Section 2) consist of:

   *  Association Type: set to 6 "SR Policy Association".

   *  Association Source (IPv4/IPv6): set to the headend IP address.

   *  Association ID (16-bit): set to "1" (this 16-bit field is not
      utilized, just set to a fixed value).

   *  Extended Association ID TLV: encodes the Color and Endpoint of the
      SR Policy.

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   The Association Source MUST be set to the headend value of the SR
   Policy, as defined in [RFC9256] Section 2.1.

   The 16-bit Association ID field in the ASSOCIATION object MUST be set
   to the value of "1".

   The Extended Association ID TLV MUST be included and it MUST be in
   the following format:

       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 = 31           |       Length = 8 or 20        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                             Color                             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      ~                           Endpoint                            ~
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                Figure 1: Extended Association ID TLV format

   Type: Extended Association ID TLV, type = 31 [RFC8697].

   Length: Either 8 or 20, depending on whether IPv4 or IPv6 address is
   encoded in the Endpoint field.

   Color: SR Policy color value, non-zero as per [RFC9256] Section 2.1.

   Endpoint: can be either IPv4 or IPv6.  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.

   If the PCEP speaker receives an SRPA object whose Association
   Parameters do not follow the above specification, then the PCEP
   speaker MUST send PCErr message with Error-Type = 26 "Association
   Error", Error-Value = 20 "SR Policy Identifier Mismatch".

   The purpose of choosing the Association Parameters in this way is 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 [RFC9256] parameters.  Thus, there is no
   chance that different PCEP speakers will come up with different
   Association Parameters for the same SR Policy.

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   The last hop of the 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 go the rest of the way to the
   Endpoint node using the native IGP 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 head-end to
   steer traffic with that Endpoint IP into the SR Policy.  Destination
   of the SR Policy Candidate Path is signaled using the END-POINTS
   object and/or LSP-IDENTIFIERS TLV, as per the usual PCEP procedures.
   When neither END-POINTS object nor LSP-IDENTIFIERS TLV is present,
   the PCEP speaker MUST extract the destination from the Endpoint field
   in the SRPA Extended Association ID TLV.

4.2.  Association Information

   The SRPA object may carry the following TLVs:

   *  SRPOLICY-POL-NAME TLV: (optional) encodes SR Policy Name string.

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

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

   *  SRPOLICY-CPATH-PREFERENCE TLV: (optional) encodes SR Policy
      Candidate Path preference value.

   Out of these TLVs, the SRPOLICY-CPATH-ID TLV is mandatory, all others
   are optional.  When a mandatory TLV is missing from the 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".

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

4.2.1.  SR Policy Name TLV

   The SRPOLICY-POL-NAME TLV is an optional TLV for the SRPA object.

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       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: The SRPOLICY-POL-NAME TLV format

   Type: 56 for "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.

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

4.2.2.  SR Policy Candidate Path Identifier TLV

   The SRPOLICY-CPATH-ID TLV 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 |                      MBZ                      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         Originator ASN                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      |                       Originator Address                      |
      |                                                               |
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         Discriminator                         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                 Figure 3: The SRPOLICY-CPATH-ID TLV format

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

   Length: 28.

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   Protocol Origin: 8-bit value that encodes the protocol origin, as
   specified in Section 6.5.  Note that in PCInitiate message [RFC8281],
   the Protocol Origin is always set to 10 (PCEP).

   MBZ: Must be zero.

   Originator ASN: Represented as 4-byte number, part of the originator
   identifier, as specified in [RFC9256] Section 2.4.  If 2-byte ASNs
   are in use, the low-order 16 bits is used, and the high-order bits
   are set to 0.  When sending PCInitiate message [RFC8281], the PCE is
   acting as the originator and therefore MUST set this to an ASN that
   it belongs to.

   Originator Address: Represented as 128-bit value where IPv4 address
   is encoded in lowest 32 bits and high-order bits are set to 0, part
   of the originator identifier, as specified in [RFC9256] Section 2.4.
   When sending PCInitiate message, the PCE is acting as the originator
   and therefore MUST set this to an address that it owns.

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

4.2.3.  SR Policy Candidate Path Name TLV

   The SRPOLICY-CPATH-NAME TLV is an optional 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            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      ~                 SR Policy Candidate Path Name                 ~
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                Figure 4: The SRPOLICY-CPATH-NAME TLV format

   Type: 58 for "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.

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

4.2.4.  SR Policy Candidate Path Preference TLV

   The SRPOLICY-CPATH-PREFERENCE TLV is an optional TLV for the SRPA
   object.  If the TLV is absent, then default Preference value is 100,
   as 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: The SRPOLICY-CPATH-PREFERENCE TLV format

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

   Length: 4.

   Preference: Numerical preference of the Candidate Path as defined in
   Section 2.7 of [RFC9256].

5.  Other Mechanisms

   This section describes mechanisms that are standardized for SR
   Policies in [RFC9256], but do not make use of the SRPA for signaling
   in PCEP.  Since SRPA is not used, there needs to be a separate
   capability negotiation.

   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.  SR Policy Capability TLV

   The SRPOLICY-CAPABILITY TLV is an optional TLV for the OPEN object.
   It is used at session establishment time to learn the other PCEP
   peer's capabilities with respect to SR Policy.

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       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|S|I|E|P|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                Figure 6: The SRPOLICY-CAPABILITY TLV format

   Type: 71 for "SRPOLICY-CAPABILITY TLV.

   Length: 4.

   P-flag: If set to '1' by a PCEP speaker, the P flag indicates that
   the PCEP speaker supports the handling of COMPUTATION-PRIORITY TLV
   for the SR Policy, see Section 5.2.  If this flag is not set, then
   the PCEP speaker MUST NOT send the COMPUTATION-PRIORITY TLV and
   SHOULD ignore it on receipt.

   E-Flag: If set to '1' by a PCEP speaker, the E flag indicates that
   the PCEP speaker supports the handling of ENLP TLV for the SR Policy,
   see Section 5.3.  If this flag is not set, then the PCEP speaker MUST
   NOT send the ENLP TLV and SHOULD ignore it on receipt.

   I-Flag: If set to '1' by a PCEP speaker, the I flag indicates that
   the PCEP speaker supports the handling of INVALIDATION TLV for the SR
   Policy, see Section 5.4.  If this flag is not set, then the PCEP
   speaker MUST NOT send the INVALIDATION TLV and SHOULD ignore it on
   receipt.

   S-Flag: If set to '1' by a PCEP speaker, the S flag indicates that
   the PCEP speaker supports the handling of "Specified-BSID-only"
   behavior for the SR Policy, see Section 5.5.  If this flag is not
   set, then the PCEP speaker MUST NOT set the Specified-BSID-only flag
   in the TE-PATH-BINDING TLV and SHOULD ignore it on receipt.

   L-Flag: 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, see Section 5.6.  If the PCE did not set this flag
   then the PCC SHOULD 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.

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5.2.  Computation Priority TLV

   The COMPUTATION-PRIORITY TLV is an optional TLV for the LSP object.
   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, 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    |                     MBZ                      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

               Figure 7: The COMPUTATION-PRIORITY TLV format

   Type: 68 for "COMPUTATION-PRIORITY" TLV.

   Length: 4.

   Priority: Numerical priority with which this LSP is to be recomputed
   by the PCE upon topology change.

5.3.  Explicit Null Label Policy (ENLP) TLV

   To steer an unlabeled IP packet into an SR policy, it is necessary to
   create a label stack for that packet, and push one or more labels
   onto that stack.  The Explicit NULL Label Policy (ENLP) TLV is an
   optional TLV 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 SRPM as described
   in section 4.1 of [RFC9256].  If an ENLP 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
   PCEP speaker SHOULD 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        |                     MBZ                      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

         Figure 8: The Explicit Null Label Policy (ENLP) TLV format

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   Type: 69 for "ENLP" TLV.

   Length: 4.

   ENLP (Explicit NULL Label Policy): 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 section Section 6.6.

   The ENLP reserved values may be used for future extensions and
   implementations SHOULD ignore the ENLP TLV with these values.  The
   behavior signaled in this TLV MAY be overridden by local
   configuration.  The section 4.1 of [RFC9256] describes the behavior
   on the headend for the handling of the explicit null label.

5.4.  Invalidation TLV

   The INVALIDATION TLV is an optional TLV for the LSP object.  It is
   used to control traffic steering into the LSP during the time 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 and traffic that would have been destined
   to that LSP is redirected somewhere else, such as via IGP or via
   another LSP.  The Drop-upon-invalid behavior specifies that the LSP
   keeps attracting traffic and the traffic has to be dropped at the
   head-end.  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: PCE specifies to the PCC whether to enable or disable
      Drop-upon-invalid (Config).

   *  PCC -> PCE: 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      |              MBZ              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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                   Figure 9: The INVALIDATION TLV format

   Type: 70 for "INVALIDATION" TLV.

   Length: 4.

   Oper: encodes the current state of the LSP, i.e., whether it is
   actively dropping traffic right now.  This field can be set to non-
   zero values only by the PCC, it MUST be set to 0 by the PCE and
   SHOULD be ignored by the PCC.

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

             Figure 10: Oper state of Drop-upon-invalid feature

   *  D: dropping - the LSP is currently attracting traffic and actively
      dropping it.

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

   Config: encodes the current setting of the Drop-upon-invalid feature.

                               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.

5.4.1.  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 essentially the whole SR Policy has
   the feature enabled.  As stated in [RFC9256] Section 8.1, the SR
   Policy is invalid when all its Candidate Paths are invalid, therefore

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   all Candidate Paths MUST be attempted for bringup before the SR
   Policy is declared invalid.

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

5.5.  Specified-BSID-only

   Specified-BSID-only functionality is defined in Section 6.2.3 of
   [RFC9256].  When specified-BSID-only is enabled for a particular
   binding SID, it means that the given binding SID is required to be
   allocated and programmed for the LSP to be operationally up.  If the
   binding SID cannot be allocated or programmed for some reason, then
   the LSP must stay down.

   To signal specified-BSID-only, a new bit: S (Specified-BSID-only) is
   allocated in the "TE-PATH-BINDING TLV Flag field" of the TE-PATH-
   BINDING TLV [I-D.ietf-pce-binding-label-sid].  When this bit is set
   for a particular BSID, it means that the BSID follows the Specified-
   BSID-only behavior.  It is possible to have a mix of BSIDs for the
   same LSP: some with S=1 and some with S=0.

5.6.  Stateless Operation

   [RFC8231] Section 5.8.2, 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 [RFC8231] Section 5.8.2, by
   making this section 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 SHOULD 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.

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

6.  IANA Considerations

6.1.  Association Type

   This document defines a new association type: SR Policy Association.
   IANA is requested to make the following codepoint assignment in the
   "ASSOCIATION Type Field" subregistry [RFC8697] within the "Path
   Computation Element Protocol (PCEP) Numbers" registry:

   +-----------+-------------------------------------------+-----------+
   | Type      | Name                                      | Reference |
   +-----------+-------------------------------------------+-----------+
   | 6         | SR Policy Association                     | This.I-D  |
   +-----------+-------------------------------------------+-----------+

6.2.  PCEP TLV Type Indicators

   This document defines eight new TLVs for carrying additional
   information about SR Policy and SR Candidate Paths.  IANA is
   requested to make the assignment of a new value for the existing
   "PCEP TLV Type Indicators" subregistry as follows:

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

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6.3.  PCEP Errors

   This document defines one new Error-Value within the "Mandatory
   Object Missing" Error-Type and two new Error-Values within the
   "Association Error" Error-Type.  IANA is requested to allocate new
   error values within the "PCEP-ERROR Object Error Types and Values"
   subregistry of the PCEP Numbers registry, as follows:

   +------------+------------------+-----------------------+-----------+
   | Error-Type | Meaning          | Error-value           | Reference |
   +------------+------------------+-----------------------+-----------+
   | 6          | Mandatory Object |                       | [RFC5440] |
   |            | Missing          |                       |           |
   +------------+------------------+-----------------------+-----------+
   |            |                  | 21: Missing SR        | This.I-D  |
   |            |                  | Policy Mandatory TLV  |           |
   +------------+------------------+-----------------------+-----------+
   | 26         | Association      |                       | [RFC8697] |
   |            | Error            |                       |           |
   +------------+------------------+-----------------------+-----------+
   |            |                  | 20: SR Policy         | This.I-D  |
   |            |                  | Identifers Mismatch   |           |
   +------------+------------------+-----------------------+-----------+
   |            |                  | 21: SR Policy         | This.I-D  |
   |            |                  | Candidate Path        |           |
   |            |                  | Identifier Mismatch   |           |
   +------------+------------------+-----------------------+-----------+

6.4.  TE-PATH-BINDING TLV Flag field

   IANA is requested to allocate new bit within the "TE-PATH-BINDING TLV
   Flag field" subregistry of the PCEP Numbers registry, as follows:

   +------------+------------------------------------------+-----------+
   | Bit position | Description                            | Reference |
   +--------------+----------------------------------------+-----------+
   | 1            | S (Specified-BSID-only)                | This.I-D  |
   +--------------+----------------------------------------+-----------+

6.5.  SR Policy Candidate Path Protocol Origin field

   This document requests IANA to maintain a new registry under "Segment
   Routing" registry group.  New values are to be assigned by "Standards
   Action" [RFC8126].  The new subregistry is requested to be created
   under it be called "SR Policy Protocol Origin".  The subregistry
   contains the following codepoints, with initial values, to be
   assigned by IANA with the reference set to this document:

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   +------------+------------------------------------------------------+
   | Value        | Description                                        |
   +--------------+----------------------------------------------------+
   | 0            | Reserved (not to be used)                          |
   +--------------+----------------------------------------------------+
   | 1-9          | Unassigned                                         |
   +--------------+----------------------------------------------------+
   | 10           | PCEP                                               |
   +--------------+----------------------------------------------------+
   | 11-19        | Unassigned                                         |
   +--------------+----------------------------------------------------+
   | 20           | BGP SR Policy                                      |
   +--------------+----------------------------------------------------+
   | 21-29        | Unassigned                                         |
   +--------------+----------------------------------------------------+
   | 30           | Configuration (CLI, YANG model via NETCONF, etc.)  |
   +--------------+----------------------------------------------------+
   | 31-250       | Unassigned                                         |
   +--------------+----------------------------------------------------+
   | 251 - 255    | Private Use (not to be assigned by IANA)           |
   +--------------+----------------------------------------------------+

6.6.  SR Policy Explicit Null Label Policy field

   This document requests IANA to maintain a new registry under "Segment
   Routing" registry group.  New values are to be assigned by "Standards
   Action" [RFC8126].  The new subregistry is requested to be created
   under it be called "SR Policy Explicit Null Label Policy".  The
   subregistry contains the following codepoints, with initial values,
   to be assigned by IANA with the reference set to this document:

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   +----------+--------------------------------------------------------+
   | Value    | Description                                            |
   +----------+--------------------------------------------------------+
   | 0        | Reserved (not to be used).                             |
   +----------+--------------------------------------------------------+
   | 1        | Push an IPv4 Explicit NULL label on an unlabeled IPv4  |
   |          | packet, but do not push an IPv6 Explicit NULL label on |
   |          | an unlabeled IPv6 packet.                              |
   +----------+--------------------------------------------------------+
   | 2        | Push an IPv6 Explicit NULL label on an unlabeled IPv6  |
   |          | packet, but do not push an IPv4 Explicit NULL label on |
   |          | an unlabeled IPv4 packet.                              |
   +----------+--------------------------------------------------------+
   | 3        | Push an IPv4 Explicit NULL label on an unlabeled IPv4  |
   |          | packet, and push an IPv6 Explicit NULL label on an     |
   |          | unlabeled IPv6 packet.                                 |
   +----------+--------------------------------------------------------+
   | 4        | Do not push an Explicit NULL label.                    |
   +----------+--------------------------------------------------------+
   | 5 - 255  | Reserved.                                              |
   +----------+--------------------------------------------------------+

7.  Implementation Status

   [Note to the RFC Editor - remove this section before publication, as
   well as remove the reference to RFC 7942.]

   This section records the status of known implementations of the
   protocol defined by this specification at the time of posting of this
   Internet-Draft, and is based on a proposal described in [RFC7942].
   The description of implementations in this section is intended to
   assist the IETF in its decision processes in progressing drafts to
   RFCs.  Please note that the listing of any individual implementation
   here does not imply endorsement by the IETF.  Furthermore, no effort
   has been spent to verify the information presented here that was
   supplied by IETF contributors.  This is not intended as, and must not
   be construed to be, a catalog of available implementations or their
   features.  Readers are advised to note that other implementations may
   exist.

   According to [RFC7942], "this will allow reviewers and working groups
   to assign due consideration to documents that have the benefit of
   running code, which may serve as evidence of valuable experimentation
   and feedback that have made the implemented protocols more mature.
   It is up to the individual working groups to use this information as
   they see fit".

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7.1.  Cisco

   *  Organization: Cisco Systems

   *  Implementation: IOS-XR PCC and PCE.

   *  Description: All features supported except Computation Priority,
      Explicit NULL and Invalidation Drop.

   *  Maturity Level: Production.

   *  Coverage: Full.

   *  Contact: ssidor@cisco.com

7.2.  Juniper

   *  Organization: Juniper Networks

   *  Implementation: PCC and PCE.

   *  Description: Everything in -05 except SR Policy Name TLV and SR
      Policy Candidate Path Name TLV.

   *  Maturity Level: Production.

   *  Coverage: Partial.

   *  Contact: cbarth@juniper.net

8.  Security Considerations

   The information carried in the newly defined SRPA object and TLVs
   could provide an eavesdropper with additional information about the
   SR Policy.  Thus securing the PCEP session using Transport Layer
   Security (TLS) [RFC8253], as per the recommendations and best current
   practices in [RFC7525], is RECOMMENDED.

9.  Acknowledgement

   Would like to thank Stephane Litkowski, Boris Khasanov, Abdul Rehman,
   Alex Tokar, Praveen Kumar and Tom Petch for review and suggestions.

10.  References

10.1.  Normative References

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   [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>.

   [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>.

   [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>.

   [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>.

   [RFC7942]  Sheffer, Y. and A. Farrel, "Improving Awareness of Running
              Code: The Implementation Status Section", BCP 205,
              RFC 7942, DOI 10.17487/RFC7942, July 2016,
              <https://www.rfc-editor.org/info/rfc7942>.

   [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>.

   [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>.

   [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>.

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   [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>.

   [RFC7525]  Sheffer, Y., Holz, R., and P. Saint-Andre,
              "Recommendations for Secure Use of Transport Layer
              Security (TLS) and Datagram Transport Layer Security
              (DTLS)", RFC 7525, DOI 10.17487/RFC7525, May 2015,
              <https://www.rfc-editor.org/info/rfc7525>.

   [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>.

   [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>.

   [I-D.ietf-pce-binding-label-sid]
              Sivabalan, S., Filsfils, C., Tantsura, J., Previdi, S.,
              and C. Li, "Carrying Binding Label/Segment Identifier
              (SID) in PCE-based Networks.", Work in Progress, Internet-
              Draft, draft-ietf-pce-binding-label-sid-16, 27 March 2023,
              <https://datatracker.ietf.org/doc/html/draft-ietf-pce-
              binding-label-sid-16>.

10.2.  Informative References

   [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-10, 16
              January 2024, <https://datatracker.ietf.org/doc/html/
              draft-ietf-pce-multipath-10>.

Appendix A.  Contributors

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   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

   Samuel Sidor
   Cisco Systems, Inc.
   Eurovea Central 3.
   Pribinova 10
   811 09 Bratislava
   Slovakia

   Email: ssidor@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

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   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

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