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Path Computation Element Communication Protocol (PCEP) Extensions for IPv6 Segment Routing
draft-ietf-pce-segment-routing-ipv6-25

Document Type Active Internet-Draft (pce WG)
Authors Cheng Li , Prejeeth Kaladharan , Siva Sivabalan , Mike Koldychev , Yongqing Zhu
Last updated 2024-06-20 (Latest revision 2024-04-04)
Replaces draft-negi-pce-segment-routing-ipv6
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Details
draft-ietf-pce-segment-routing-ipv6-25
PCE Working Group                                                  C. Li
Internet-Draft                                       Huawei Technologies
Intended status: Standards Track                           P. Kaladharan
Expires: 6 October 2024                                      RtBrick Inc
                                                            S. Sivabalan
                                                       Ciena Corporation
                                                            M. Koldychev
                                                     Cisco Systems, Inc.
                                                                  Y. Zhu
                                                           China Telecom
                                                            4 April 2024

 Path Computation Element Communication Protocol (PCEP) Extensions for
                          IPv6 Segment Routing
                 draft-ietf-pce-segment-routing-ipv6-25

Abstract

   Segment Routing (SR) can be used to steer packets through a network
   using the IPv6 or MPLS data plane, employing the source routing
   paradigm.

   A Segment Routed Path can be derived from a variety of mechanisms,
   including an IGP Shortest Path Tree (SPT), explicit configuration, or
   a Path Computation Element(PCE).

   Since SR can be applied to both MPLS and IPv6 data-planes, a PCE
   should be able to compute an SR Path for both MPLS and IPv6 data-
   planes.  The Path Computation Element communication Protocol (PCEP)
   extension and mechanisms to support SR-MPLS have been defined.  This
   document outlines the necessary extensions to support SR for the IPv6
   data-plane within PCEP.

Status of This Memo

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

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

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

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   This Internet-Draft will expire on 6 October 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
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   4
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Overview of PCEP Operation in SRv6 Networks . . . . . . . . .   5
     3.1.  Operation Overview  . . . . . . . . . . . . . . . . . . .   6
     3.2.  SRv6-Specific PCEP Message Extensions . . . . . . . . . .   6
   4.  Object Formats  . . . . . . . . . . . . . . . . . . . . . . .   6
     4.1.  The OPEN Object . . . . . . . . . . . . . . . . . . . . .   6
       4.1.1.  The SRv6 PCE Capability sub-TLV . . . . . . . . . . .   6
     4.2.  The RP/SRP Object . . . . . . . . . . . . . . . . . . . .   8
     4.3.  ERO . . . . . . . . . . . . . . . . . . . . . . . . . . .   8
       4.3.1.  SRv6-ERO Subobject  . . . . . . . . . . . . . . . . .   8
         4.3.1.1.  SID Structure . . . . . . . . . . . . . . . . . .  11
         4.3.1.2.  Order of the Optional fields  . . . . . . . . . .  12
     4.4.  RRO . . . . . . . . . . . . . . . . . . . . . . . . . . .  12
       4.4.1.  SRv6-RRO Subobject  . . . . . . . . . . . . . . . . .  13
   5.  Procedures  . . . . . . . . . . . . . . . . . . . . . . . . .  13
     5.1.  Exchanging the SRv6 Capability  . . . . . . . . . . . . .  14
     5.2.  ERO Processing  . . . . . . . . . . . . . . . . . . . . .  15
       5.2.1.  SRv6 ERO Validation . . . . . . . . . . . . . . . . .  15
       5.2.2.  Interpreting the SRv6-ERO . . . . . . . . . . . . . .  16
     5.3.  RRO Processing  . . . . . . . . . . . . . . . . . . . . .  16
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  17
   7.  Manageability Considerations  . . . . . . . . . . . . . . . .  17
     7.1.  Control of Function and Policy  . . . . . . . . . . . . .  17
     7.2.  Information and Data Models . . . . . . . . . . . . . . .  18
     7.3.  Liveness Detection and Monitoring . . . . . . . . . . . .  18
     7.4.  Verify Correct Operations . . . . . . . . . . . . . . . .  18
     7.5.  Requirements On Other Protocols . . . . . . . . . . . . .  18
     7.6.  Impact On Network Operations  . . . . . . . . . . . . . .  18

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   8.  Implementation Status . . . . . . . . . . . . . . . . . . . .  18
     8.1.  Cisco's Commercial Delivery . . . . . . . . . . . . . . .  19
     8.2.  Huawei's Commercial Delivery  . . . . . . . . . . . . . .  19
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  19
     9.1.  PCEP ERO and RRO subobjects . . . . . . . . . . . . . . .  19
     9.2.  New SRv6-ERO NAI Type Registry  . . . . . . . . . . . . .  20
     9.3.  New SRv6-ERO Flag Registry  . . . . . . . . . . . . . . .  20
     9.4.  LSP-ERROR-CODE TLV  . . . . . . . . . . . . . . . . . . .  21
     9.5.  PATH-SETUP-TYPE-CAPABILITY Sub-TLV Type Indicators  . . .  21
     9.6.  SRv6 PCE Capability Flags . . . . . . . . . . . . . . . .  21
     9.7.  New Path Setup Type . . . . . . . . . . . . . . . . . . .  22
     9.8.  ERROR Objects . . . . . . . . . . . . . . . . . . . . . .  22
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  23
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  23
     10.2.  Informative References . . . . . . . . . . . . . . . . .  24
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  26
   Contributors  . . . . . . . . . . . . . . . . . . . . . . . . . .  26
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  27

1.  Introduction

   As defined in [RFC8402], Segment Routing (SR) architecture allows the
   source node to steer a packet through a path indicated by an ordered
   list of instructions, called segments.  A segment can represent any
   instruction, topological or service-based, and it can have a semantic
   local to an SR node or global within an SR domain.

   [RFC5440] describes Path Computation Element communication Protocol
   (PCEP) for communication between a Path Computation Client (PCC) and
   a PCE or between a pair of PCEs.  A PCE or a PCC operating as a PCE
   (in a hierarchical PCE environment) computes paths for MPLS Traffic
   Engineering LSPs (MPLS-TE LSPs) based on various constraints and
   optimization criteria.

   [RFC8231] specifies extensions to PCEP that allow a stateful PCE to
   compute and recommend network paths in compliance with [RFC4657] and
   defines objects and TLVs for MPLS-TE LSPs.  Stateful PCEP extensions
   provide synchronization of LSP state between a PCC and a PCE or
   between a pair of PCEs, delegation of LSP control, reporting of LSP
   state from a PCC to a PCE, controlling the setup and path routing of
   an LSP from a PCE to a PCC.  Stateful PCEP extensions are intended
   for an operational model in which LSPs are configured on the PCC, and
   control over them is delegated to the PCE.

   A mechanism to dynamically initiate LSPs on a PCC based on the
   requests from a stateful PCE or a controller using stateful PCE is
   specified in [RFC8281].  As per [RFC8664], it is possible to use a
   stateful PCE for computing one or more SR-TE paths taking into

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   account various constraints and objective functions.  Once a path is
   computed, the stateful PCE can initiate an SR-TE path on a PCC using
   PCEP extensions specified in [RFC8281] and the SR-specific PCEP
   extensions specified in [RFC8664].

   [RFC8664] specifies PCEP extensions for supporting a SR-TE LSP for
   the MPLS data-plane.  This document extends [RFC8664] to support SR
   for the IPv6 data-plane.  Additionally, using procedures described in
   this document, a PCC can request an SRv6 path from either a stateful
   or stateless PCE.  This specification relies on the PATH-SETUP-TYPE
   TLV and procedures specified in [RFC8408].

   This specification provides a mechanism for a network controller
   (acting as a PCE) to instantiate candidate paths for an SR Policy
   onto a head-end node (acting as a PCC) using PCEP.  For more
   information on the SR Policy Architecture, see [RFC9256] which
   applies to both SR-MPLS and SRv6.

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]: PCC,
   PCE, PCEP, PCEP Peer.

   This document uses the following terms defined in [RFC8051]: Stateful
   PCE, Delegation.

   Further, the following terms are used in the document,

   MSD:  Maximum SID Depth.

   PST:  Path Setup Type.

   SR:  Segment Routing.

   SID:  Segment Identifier.

   SRv6:  Segment Routing over IPv6 data-plane.

   SRH:  IPv6 Segment Routing Header [RFC8754].

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   SRv6 Path:  IPv6 Segment List (List of IPv6 SIDs representing a path
      in IPv6 SR domain in the context of this document)

   Further, note that the term LSP used in the PCEP specifications,
   would be equivalent to an SRv6 Path (represented as a list of SRv6
   segments) in the context of supporting SRv6 in PCEP.

3.  Overview of PCEP Operation in SRv6 Networks

   Basic operations for PCEP speakers are built on [RFC8664].

   In PCEP messages, route information is carried in the Explicit Route
   Object (ERO), which consists of a sequence of subobjects.  [RFC8664]
   defined a new Explicit Route Object (ERO) subobject denoted by "SR-
   ERO subobject" capable of carrying a SID as well as the identity of
   the node/adjacency represented by the SID for SR-MPLS.  SR-capable
   PCEP speakers can generate and/or process such an ERO subobject.  An
   ERO containing SR-ERO subobjects can be included in the PCEP Path
   Computation Reply (PCRep) message defined in [RFC5440], the PCEP LSP
   Initiate Request message (PCInitiate) defined in [RFC8281], as well
   as in the PCEP LSP Update Request (PCUpd) and PCEP LSP State Report
   (PCRpt) messages defined in [RFC8231].  [RFC8664] also defines a new
   Reported Route Object(RRO) called SR-RRO to represent the SID list
   that was applied by the PCC, that is, the actual path taken by the
   LSP in SR-MPLS network.

   The SRv6 Paths computed by a PCE can be represented as an ordered
   list of SRv6 segments.  This document defines new subobjects
   "SRv6-ERO" and "SRv6-RRO" in the ERO and the RRO respectively to
   carry the SRv6 SID.  SRv6-capable PCEP speakers MUST be able to
   generate and/or process these subobjects.

   When a PCEP session between a PCC and a PCE is established, both PCEP
   speakers exchange their capabilities to indicate their ability to
   support SRv6 specific functionality as described in Section 4.1.1.

   In summary, this document,

   *  Defines a new PCEP capability for SRv6.

   *  Defines a new subobject SRv6-ERO in ERO.

   *  Defines a new subobject SRv6-RRO in RRO.

   *  Defines a new path setup type (PST) [RFC8408] carried in the PATH-
      SETUP-TYPE TLV and the PATH-SETUP-TYPE-CAPABILITY TLV.

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3.1.  Operation Overview

   In SR networks, an SR source node [RFC8754] steers a packet into an
   SR Policy resulting in a segment list.

   When SR leverages the IPv6 data-plane (i.e.  SRv6), the PCEP
   procedures and mechanisms are extended in this document.

   This document describes the extension to support SRv6 in PCEP.  A PCC
   or PCE indicates its ability to support SRv6 during the PCEP session
   Initialization Phase via a new SRv6-PCE-CAPABILITY sub-TLV (see
   details in Section 4.1.1).

3.2.  SRv6-Specific PCEP Message Extensions

   As defined in [RFC5440], a PCEP message consists of a common header
   followed by a variable length body made up of mandatory and/or
   optional objects.  This document does not require any changes in the
   format of PCReq and PCRep messages specified in [RFC5440], PCInitiate
   message specified in [RFC8281], and PCRpt and PCUpd messages
   specified in [RFC8231].  However, PCEP messages pertaining to SRv6
   MUST include PATH-SETUP-TYPE TLV in the RP (Request Parameters) or
   SRP (Stateful PCE Request Parameters) object to clearly identify that
   SRv6 is intended.

4.  Object Formats

4.1.  The OPEN Object

4.1.1.  The SRv6 PCE Capability sub-TLV

   This document defines a new Path Setup Type (PST) [RFC8408] for SRv6,
   as follows.

   *  PST = 3 : Path is setup using SRv6.

   A PCEP speaker indicates its support of the function described in
   this document by sending a PATH-SETUP-TYPE-CAPABILITY TLV in the OPEN
   object with this new PST "3" included in the PST list.

   This document also defines the SRv6-PCE-CAPABILITY sub-TLV.  PCEP
   speakers use this sub-TLV to exchange information about their SRv6
   capability.  If a PCEP speaker includes PST=3 in the PST List of the
   PATH-SETUP-TYPE-CAPABILITY TLV then it MUST also include the SRv6-
   PCE-CAPABILITY sub-TLV inside the PATH-SETUP-TYPE-CAPABILITY TLV.
   For further error handling, please see Section 5.

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   The format of the SRv6-PCE-CAPABILITY sub-TLV is shown in the
   following figure.

    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=27            |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Reserved           |             Flags         |N| |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   MSD-Type    | MSD-Value     |   MSD-Type    | MSD-Value     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   //                             ...                             //
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   MSD-Type    | MSD-Value     |           Padding             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                Figure 1: SRv6-PCE-CAPABILITY sub-TLV format

   The code point for the TLV type is 27 and the format is compliant
   with the PCEP TLV format defined in [RFC5440].  That is, the sub-TLV
   is composed of 2 octets for the type, 2 octets specifying the length,
   and a Value field.  The Type field when set to 27 identifies the
   SRv6-PCE-CAPABILITY sub-TLV and the presence of the sub-TLV indicates
   the support for the SRv6 paths in PCEP.  The Length field defines the
   length of the value portion in octets.  The sub-TLV is padded to
   4-octet alignment, and padding is not included in the Length field.
   The (MSD-Type,MSD-Value) pairs are OPTIONAL.  The number of (MSD-
   Type,MSD-Value) pairs can be determined from the Length field of the
   TLV.

   The value comprises of -

      Reserved: 2 octet, this field MUST be set to 0 on transmission,
      and ignored on receipt.

      Flags: 2 octet, one bit is currently assigned in this document.
      Section 9.6

      -  N bit (bit position 14): A PCC sets this flag bit to 1 to
         indicate that it is capable of resolving a Node or Adjacency
         Identifier (NAI) to an SRv6-SID.

      -  Unassigned bits MUST be set to 0 on transmission and ignored on
         receipt

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      A pair of (MSD-Type, MSD-Value): Where MSD-Type (1 octet) is as
      per the IGP MSD Type registry created by [RFC8491] and populated
      with SRv6 MSD types as per [RFC9352]; MSD-Value (1 octet) is as
      per [RFC8491].

   The SRv6 MSD information advertised via SRv6-PCE-Capability sub-TLV
   conveys the SRv6 capabilities of the PCEP speaker alone.  However,
   when it comes to the computation of an SR Policy for the SRv6 data-
   plane, the SRv6 MSD capabilities of all the intermediate SRv6
   Endpoint node as well as the tail-end node also need to be considered
   to ensure those midpoints are able to correctly process their
   segments and for the tail-end to dispose of the SRv6 encapsulation.
   The SRv6 MSD capabilities of other nodes might be learned as part of
   the topology information via BGP-LS[RFC9514] or via PCEP if the PCE
   also happens to have PCEP sessions to those nodes.

   It is recommended that the SRv6 MSD information be not included in
   the SRv6-PCE-Capability sub-TLV in deployments where the PCE is able
   to obtain this via IGP/BGP-LS as part of the topology information.

4.2.  The RP/SRP Object

   This document defines a new Path Setup Type (PST=3) for SRv6.  In
   order to indicate that the path is for SRv6, any RP or SRP object
   MUST include the PATH-SETUP-TYPE TLV as specified in [RFC8408], where
   PST is set to 3.

4.3.  ERO

   In order to support SRv6, a new "SRv6-ERO" subobject is defined for
   inclusion in the ERO.

4.3.1.  SRv6-ERO Subobject

   An SRv6-ERO subobject is formatted as shown in the following figure.

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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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |L|   Type=40   |     Length    | NT    |     Flags     |V|T|F|S|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |              Reserved         |      Endpoint Behavior        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      |                   SRv6 SID (conditional)                      |
      |                        (128-bit)                              |
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      //                 NAI (variable, conditional)                 //
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      |                  SID Structure (conditional)                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                    Figure 2: SRv6-ERO Subobject Format

   The fields in the SRv6-ERO subobject are as follows:

   The 'L' Flag: Indicates whether the subobject represents a loose-hop
   (see [RFC3209]).  If this flag is set to zero, a PCC MUST NOT
   overwrite the SID value present in the SRv6-ERO subobject.
   Otherwise, a PCC MAY expand or replace one or more SID values in the
   received SRv6-ERO based on its local policy.

   Type: indicates the content of the subobject, i.e. when the field is
   set to 40, the suboject is an SRv6-ERO subobject representing an SRv6
   SID.

   Length: Contains the total length of the subobject in octets.  The
   Length MUST be at least 24, and MUST be a multiple of 4.  An SRv6-ERO
   subobject MUST contain at least one of an SRv6-SID or an NAI.  The S
   and F bit in the Flags field indicates whether the SRv6-SID or NAI
   fields are absent.

   NAI Type (NT): Indicates the type and format of the NAI contained in
   the object body, if any is present.  If the F bit is set to one (see
   below) then the NT field has no meaning and MUST be ignored by the
   receiver.  This document creates a new PCEP SRv6-ERO NAI Types
   registry in Section 9.2 and allocates the following values.

      If NT value is 0, the NAI MUST NOT be included.

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      When NT value is 2, the NAI is as per the 'IPv6 Node ID' format
      defined in [RFC8664], which specifies an IPv6 address.  This is
      used to identify the owner of the SRv6 Identifier.  This is
      optional, as the LOC (the locator portion) of the SRv6 SID serves
      a similar purpose (when present).

      When NT value is 4, the NAI is as per the 'IPv6 Adjacency' format
      defined in [RFC8664], which specify a pair of IPv6 addresses.
      This is used to identify the IPv6 Adjacency and used with the SRv6
      Adj-SID.

      When NT value is 6, the NAI is as per the 'link-local IPv6
      addresses' format defined in [RFC8664], which specify a pair of
      (global IPv6 address, interface ID) tuples.  It is used to
      identify the IPv6 Adjacency and used with the SRv6 Adj-SID.

   Flags: Used to carry additional information pertaining to the
   SRv6-SID.  This document defines the following flag bits.  The other
   bits MUST be set to zero by the sender and MUST be ignored by the
   receiver.  This document creates a new registry SRv6-ERO Flag Field
   registry in Section 9.3 and allocates the following values.

   *  S: When this bit is set to 1, the SRv6-SID value in the subobject
      body is absent.  In this case, the PCC is responsible for choosing
      the SRv6-SID value, e.g., by looking up in the SR-DB using the NAI
      which, in this case, MUST be present in the subobject.  If the S
      bit is set to 1 then F bit MUST be set to zero.

   *  F: When this bit is set to 1, the NAI value in the subobject body
      is absent.  The F bit MUST be set to 1 if NT=0, and otherwise MUST
      be set to zero.  The S and F bits MUST NOT both be set to 1.

   *  T: When this bit is set to 1, the SID Structure value in the
      subobject body is present.  The T bit MUST be set to 0 when S bit
      is set to 1.  If the T bit is set when the S bit is set, the T bit
      MUST be ignored.  Thus, the T bit indicates the presence of an
      optional 8-byte SID Structure when SRv6 SID is included.  The SID
      Structure is defined in Section 4.3.1.1.

   *  V: The "SID verification" bit usage is as per Section 5.1 of
      [RFC9256].  If a PCC "Verification fails" for a SID, it MUST
      report this error by including the LSP-ERROR-CODE TLV with LSP
      error-value "SID Verification fails" in the LSP object in the
      PCRpt message to the PCE.

   Reserved: MUST be set to zero while sending and ignored on receipt.

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   Endpoint Behavior: A 16-bit field representing the behavior
   associated with the SRv6 SIDs.  This information is optional, but it
   is recommended to signal it always if possible.  It could be used for
   maintainability and diagnostic purpose.  If behavior is not known,
   value '0xFFFF' defined in the registry "SRv6 Endpoint Behaviors" is
   used [RFC8986].

   SRv6 SID: SRv6 Identifier is an 128-bit value representing the SRv6
   segment.

   NAI: The NAI associated with the SRv6-SID.  The NAI's format depends
   on the value in the NT field, and is described in [RFC8664].

   At least one SRv6-SID or the NAI MUST be included in the SRv6-ERO
   subobject, and both MAY be included.

4.3.1.1.  SID Structure

   The SID Structure is an optional part of the SR-ERO subobject, as
   described in Section 4.3.1.

   [RFC8986] defines an SRv6 SID as consisting of LOC:FUNCT:ARG, where a
   locator (LOC) is encoded in the L most significant bits of the SID,
   followed by F bits of function (FUNCT) and A bits of arguments (ARG).
   A locator may be represented as B:N where B is the SRv6 SID locator
   block (IPv6 prefix allocated for SRv6 SIDs by the operator) and N is
   the identifier of the parent node instantiating the SID called
   locator node.

   It is formatted as shown in the following figure.

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |    LB Length  |  LN Length    | Fun. Length   |  Arg. Length  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                 Reserved                      |   Flags       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                       Figure 3: SID Structure Format

   where:

   LB Length: 1 octet.  SRv6 SID Locator Block length in bits.

   LN Length: 1 octet.  SRv6 SID Locator Node length in bits.

   Fun. Length: 1 octet.  SRv6 SID Function length in bits.

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   Arg. Length: 1 octet.  SRv6 SID Arguments length in bits.

   The sum of all four sizes in the SID Structure must be lower or equal
   to 128 bits.  If the sum of all four sizes advertised in the SID
   Structure is larger than 128 bits, the corresponding SRv6 SID MUST be
   considered invalid and a PCErr message with Error-Type = 10
   ("Reception of an invalid object") and Error-Value = 37 ("Invalid
   SRv6 SID Structure") is returned.

   Reserved: MUST be set to zero while sending and ignored on receipt.

   Flags: Currently no flags are defined.  Unassigned bits must be set
   to zero while sending and ignored on receipt.

   The SRv6 SID Structure provides the detailed encoding information of
   an SRv6 SID, which is useful in the use cases that require to know
   the SRv6 SID structure.  When a PCEP speaker receives the SRv6 SID
   and its structure information, the SRv6 SID can be parsed based on
   the SRv6 SID Structure and/or possible local policies.  The SRv6 SID
   Structure could be used by the PCE for ease of operations and
   monitoring.  For example, this information could be used for
   validation of SRv6 SIDs being instantiated in the network and checked
   for conformance to the SRv6 SID allocation scheme chosen by the
   operator as described in Section 3.2 of [RFC8986].  In the future,
   PCE might also be utilized to verify and automate the security of the
   SRv6 domain by provisioning filtering rules at the domain boundaries
   as described in Section 5 of [RFC8754].  The details of these
   potential applications are outside the scope of this document.

4.3.1.2.  Order of the Optional fields

   The optional elements in the SRv6-ERO subobject i.e. SRv6 SID, NAI
   and the SID Structure MUST be encoded in the order as depicted in
   Figure 2.  The presence or absence of each of them is indicated by
   the respective flags i.e. S flag, F flag and T flag.

   In order to ensure future compatibility, any optional elements added
   to the SRv6-ERO subobject in the future must specify their order and
   request the Internet Assigned Numbers Authority (IANA) to allocate a
   flag to indicate their presence from the subregistry created in
   Section 9.3.

4.4.  RRO

   In order to support SRv6, a new "SRv6-RRO" subobject is defined for
   inclusion in the RRO.

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4.4.1.  SRv6-RRO Subobject

   A PCC reports an SRv6 path to a PCE by sending a PCRpt message, per
   [RFC8231].  The RRO on this message represents the SID list that was
   applied by the PCC, that is, the actual path taken.  The procedures
   of [RFC8664] with respect to the RRO apply equally to this
   specification without change.

   An RRO contains one or more subobjects called "SRv6-RRO subobjects"
   whose format is shown below.

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   Type=40     |     Length    |  NT   |     Flags     |V|T|F|S|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |              Reserved         |      Endpoint Behavior        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      |                      SRv6 SID(optional)                       |
      |                           (128-bit)                           |
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      //                    NAI (variable)                           //
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      |                     SID Structure (optional)                  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                    Figure 4: SRv6-RRO Subobject Format

   The format of the SRv6-RRO subobject is the same as that of the
   SRv6-ERO subobject, but without the L flag.

   The V flag has no meaning in the SRv6-RRO and is ignored on receipt
   at the PCE.

   Ordering of SRv6-RRO subobjects by PCC in PCRpt message remains as
   per [RFC8664].

   The ordering of optional elements in the SRv6-RRO subobject is the
   same as described in Section 4.3.1.2.

5.  Procedures

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5.1.  Exchanging the SRv6 Capability

   A PCC indicates that it is capable of supporting the head-end
   functions for SRv6 by including the SRv6-PCE-CAPABILITY sub-TLV in
   the Open message that it sends to a PCE.  A PCE indicates that it is
   capable of computing SRv6 paths by including the SRv6-PCE-CAPABILITY
   sub-TLV in the Open message that it sends to a PCC.

   If a PCEP speaker receives a PATH-SETUP-TYPE-CAPABILITY TLV with a
   PST list containing PST=3, but the SRv6-PCE-CAPABILITY sub-TLV is
   absent, then the PCEP speaker MUST send a PCErr message with Error-
   Type = 10 (Reception of an invalid object) and Error-Value = 34
   (Missing PCE-SRv6-CAPABILITY sub-TLV) and MUST then close the PCEP
   session.  If a PCEP speaker receives a PATH-SETUP-TYPE-CAPABILITY TLV
   with an SRv6-PCE-CAPABILITY sub-TLV, but the PST list does not
   contain PST=3, then the PCEP speaker MUST ignore the SRv6-PCE-
   CAPABILITY sub-TLV.

   In case the MSD-Type in SRv6-PCE-CAPABILITY sub-TLV received by the
   PCE does not correspond to one of the SRv6 MSD types, the PCE MUST
   respond with a PCErr message (Error-Type = 1 "PCEP session
   establishment failure" and Error-Value = 1 "reception of an invalid
   Open message or a non Open message.").

   Note that the MSD-Type, MSD-Value exchanged via the SRv6-PCE-
   CAPABILITY sub-TLV indicates the SRv6 SID imposition limit for the
   sender PCC node only.  However, if a PCE learns these via alternate
   mechanisms, e.g. routing protocols [RFC9352], then it ignores the
   values in the SRv6-PCE-CAPABILITY sub-TLV.  Furthermore, whenever a
   PCE learns any other SRv6 MSD types that may be defined in the future
   via alternate mechanisms, it MUST use those values regardless of the
   values exchanged in the SRv6-PCE-CAPABILITY sub-TLV.

   During path computation, PCE must consider the MSD information of all
   the nodes along the path instead of only the MSD information of the
   ingress PCC since a packet may be dropped on any node in a forwarding
   path because of MSD exceeding.  The MSD capabilities of all SR nodes
   along the path can be learned as part of the topology information via
   IGP/BGP-LS or via PCEP if the PCE also happens to have PCEP sessions
   to those nodes.

   A PCE MUST NOT send SRv6 paths exceeding the SRv6 MSD capabilities of
   the PCC.  If a PCC needs to modify the SRv6 MSD value signaled via
   the Open message, it MUST close the PCEP session and re-establish it
   with the new value.  If the PCC receives an SRv6 path that exceed its
   SRv6 MSD capabilities, the PCC MUST send a PCErr message with Error-
   Type = 10 (Reception of an invalid object) and Error-Value = 39
   (Unsupported number of SRv6-ERO subobjects).

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   The N flag and (MSD-Type,MSD-Value) pair inside the SRv6-PCE-
   CAPABILITY sub-TLV are meaningful only in the Open message sent to a
   PCE.  As such, the flags MUST be set to zero and a (MSD-Type,MSD-
   Value) pair MUST NOT be present in the SRv6-PCE-CAPABILITY sub-TLV in
   an Open message sent to a PCC.  Similarly, a PCC MUST ignore flags
   and any (MSD-Type,MSD-Value) pair in a received Open message.  If a
   PCE receives multiple SRv6-PCE-CAPABILITY sub-TLVs in an Open
   message, it processes only the first sub-TLV received.

5.2.  ERO Processing

   The processing of ERO remains unchanged in accordance with both
   [RFC5440] and [RFC8664].

5.2.1.  SRv6 ERO Validation

   If a PCC does not support the SRv6 PCE Capability and thus cannot
   recognize the SRv6-ERO or SRv6-RRO subobjects, it should respond
   according to the rules for a malformed object as described in
   [RFC5440].

   On receiving an SRv6-ERO, a PCC MUST validate that the Length field,
   the S bit, the F bit, the T bit, and the NT field are consistent, as
   follows.

   *  If NT=0, the F bit MUST be 1, the S bit MUST be zero and the
      Length MUST be 24.

   *  If NT=2, the F bit MUST be zero.  If the S bit is 1, the Length
      MUST be 24, otherwise the Length MUST be 40.

   *  If NT=4, the F bit MUST be zero.  If the S bit is 1, the Length
      MUST be 40, otherwise the Length MUST be 56.

   *  If NT=6, the F bit MUST be zero.  If the S bit is 1, the Length
      MUST be 48, otherwise the Length MUST be 64.

   *  If T bit is 1, then S bit MUST be zero.

   If a PCC finds that the NT field, Length field, S bit, F bit, and T
   bit are not consistent, it MUST consider the entire ERO invalid and
   MUST send a PCErr message with Error-Type = 10 ("Reception of an
   invalid object") and Error-Value = 11 ("Malformed object").

   If a PCC does not recognize or support the value in the NT field, it
   MUST consider the entire ERO invalid and send a PCErr message with
   Error-Type = 10 ("Reception of an invalid object") and Error- value =
   40 ("Unsupported NAI Type in the SRv6-ERO/SRv6-RRO subobject").

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   If a PCC receives an SRv6-ERO subobject in which the S and F bits are
   both set to 1 (that is, both the SID and NAI are absent), it MUST
   consider the entire ERO invalid and send a PCErr message with Error-
   Type = 10 ("Reception of an invalid object") and Error-value = 41
   ("Both SID and NAI are absent in the SRv6-ERO subobject").

   If a PCC receives an SRv6-ERO subobject in which the S bit is set to
   1 and the F bit is set to zero (that is, the SID is absent and the
   NAI is present), but the PCC does not support NAI resolution, it MUST
   consider the entire ERO invalid and send a PCErr message with Error-
   Type = 4 ("Not supported object") and Error-value = 4 ("Unsupported
   parameter").

   If a PCC detects that the subobjects of an ERO are a mixture of SRv6-
   ERO subobjects and subobjects of other types, then it MUST send a
   PCErr message with Error-Type = 10 ("Reception of an invalid object")
   and Error-value = 42 ("ERO mixes SRv6-ERO subobjects with other
   subobject types").

   In case a PCEP speaker receives an SRv6-ERO subobject, when the PST
   is not set to 3 or SRv6-PCE-CAPABILITY sub-TLV was not exchanged, it
   MUST send a PCErr message with Error-Type = 19 ("Invalid Operation")
   and Error-Value = 19 ("Attempted SRv6 when the capability was not
   advertised").

   If a PCC receives an SRv6 path that exceeds the SRv6 MSD
   capabilities, it MUST send a PCErr message with Error-Type = 10
   ("Reception of an invalid object") and Error-Value = 43 ("Unsupported
   number of SRv6-ERO subobjects") as per [RFC8664].

5.2.2.  Interpreting the SRv6-ERO

   The SRv6-ERO contains a sequence of subobjects.  According to
   [RFC9256], each SRv6-ERO subobject in the sequence identifies a
   segment that the traffic will be directed to, in the order given.
   That is, the first subobject identifies the first segment the traffic
   will be directed to, the second SRv6-ERO subobject represents the
   second segment, and so on.

5.3.  RRO Processing

   The syntax checking rules that apply to the SRv6-RRO subobject are
   identical to those of the SRv6-ERO subobject, except as noted below.

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   If a PCEP speaker receives an SRv6-RRO subobject in which both SRv6
   SID and NAI are absent, it MUST consider the entire RRO invalid and
   send a PCErr message with Error-Type = 10 ("Reception of an invalid
   object") and Error-Value = 35 ("Both SID and NAI are absent in
   SRv6-RRO subobject").

   If a PCE detects that the subobjects of an RRO are a mixture of
   SRv6-RRO subobjects and subobjects of other types, then it MUST send
   a PCErr message with Error-Type = 10 ("Reception of an invalid
   object") and Error-Value = 36 ("RRO mixes SRv6-RRO subobjects with
   other subobject types").

   The mechanism by which the PCC learns the path is outside the scope
   of this document.

6.  Security Considerations

   The security considerations described in [RFC5440], section 2.5 of
   [RFC6952], [RFC8231], [RFC8281], [RFC8253] and [RFC8664] are
   applicable to this specification.

   Note that this specification enables a network controller to
   instantiate an SRv6 path in the network.  This creates an additional
   vulnerability if the security mechanisms of [RFC5440], [RFC8231], and
   [RFC8281] are not used.  If there is no integrity protection on the
   session, then an attacker could create an SRv6 path that may not
   subjected to the further verification checks.  Further, the MSD field
   in the Open message could disclose node forwarding capabilities if
   suitable security mechanisms are not in place.  Hence, securing the
   PCEP session using Transport Layer Security (TLS) [RFC8253] is
   RECOMMENDED.

7.  Manageability Considerations

   All manageability requirements and considerations listed in
   [RFC5440], [RFC8231], [RFC8281], and [RFC8664] apply to PCEP protocol
   extensions defined in this document.  In addition, requirements and
   considerations listed in this section apply.

7.1.  Control of Function and Policy

   A PCEP implementation SHOULD allow the operator to configure the SRv6
   capability.  Further a policy to accept NAI only for the SRv6 SHOULD
   be allowed to be set.

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7.2.  Information and Data Models

   The PCEP YANG module is out of the scope of this document and defined
   in other documents, for example, [I-D.ietf-pce-pcep-yang].  An
   augmented YANG module for SRv6 is also specified in another document
   [I-D.ietf-pce-pcep-srv6-yang] that allows for SRv6 capability and MSD
   configurations as well as to monitor the SRv6 paths set in the
   network.

7.3.  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].

7.4.  Verify Correct Operations

   Verification of the mechanisms defined in this document can be built
   on those already listed in [RFC5440], [RFC8231], and [RFC8664].

7.5.  Requirements On Other Protocols

   Mechanisms defined in this document do not imply any new requirements
   on other protocols.

7.6.  Impact On Network Operations

   Mechanisms defined in [RFC5440], [RFC8231], and [RFC8664] also apply
   to PCEP extensions defined in this document.

8.  Implementation Status

   [Note to the RFC Editor - remove this section before publication, as
   well as remove the reference to [RFC7942].

   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.

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   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".

8.1.  Cisco's Commercial Delivery

   *  Organization: Cisco Systems, Inc.

   *  Implementation: IOS-XR PCE and PCC.

   *  Description: Implementation with experimental codepoints.

   *  Maturity Level: Production

   *  Coverage: Partial

   *  Contact: ssidor@cisco.com

8.2.  Huawei's Commercial Delivery

   *  Organization: Huawei Technologies Co.,Ltd.

   *  Implementation: Huawei Routers and NCE Controller

   *  Description: Huawei has Implemented this draft to support PCE-
      Initiated SRv6 Policy.

   *  Maturity Level: Production

   *  Coverage: Partial

   *  Contact: yuwei.yuwei@huawei.com

9.  IANA Considerations

9.1.  PCEP ERO and RRO subobjects

   This document defines a new subobject type for the PCEP explicit
   route object (ERO), and a new subobject type for the PCEP reported
   route object (RRO).  The code points for subobject types of these
   objects is maintained in the RSVP parameters registry, under the
   EXPLICIT_ROUTE and REPORTED_ROUTE objects.  IANA is requested to
   confirm the following allocations in the RSVP Parameters registry for
   each of the new subobject types defined in this document.

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     Object                Subobject                  Subobject Type
     --------------------- -------------------------- ------------------
     EXPLICIT_ROUTE        SRv6-ERO (PCEP-specific)     40
     ROUTE_RECORD          SRv6-RRO (PCEP-specific)     40

9.2.  New SRv6-ERO NAI Type Registry

   IANA is requested to create a new sub-registry, named "PCEP SRv6-ERO
   NAI Types", within the "Path Computation Element Protocol (PCEP)
   Numbers" registry to manage the 4-bit NT field in SRv6-ERO subobject.
   The allocation policy for this new registry is by IETF
   Review[RFC8126].The new registry contains the following values.

     Value      Description                      Reference
     -----      -----------                      ---------
     0          NAI is absent.                   This document
     1          Unassigned
     2          NAI is an IPv6 node ID.          This document
     3          Unassigned
     4          NAI is an IPv6 adjacency         This document
                with global IPv6 addresses.

     5          Unassigned
     6          NAI is an IPv6 adjacency         This document
                with link-local IPv6 addresses.
     7-15       Unassigned

9.3.  New SRv6-ERO Flag Registry

   IANA is requested to create a new sub-registry, named "SRv6-ERO Flag
   Field", within the "Path Computation Element Protocol (PCEP) Numbers"
   registry to manage the 12-bit Flag field of the SRv6-ERO subobject.
   New values are to be assigned by Standards Action [RFC8126].  Each
   bit should be tracked with the following qualities.

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

   *  Description

   *  Reference

   The following values are defined in this document.

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                   Bit     Description            Reference
                   -----   ------------------     --------------
                    0-7      Unassigned
                      8      SID Verification (V)  This document
                      9      SID Structure is      This document
                             present (T)
                     10      NAI is absent (F)     This document
                     11      SID is absent (S)     This document

9.4.  LSP-ERROR-CODE TLV

   This document defines a new value in the sub-registry "LSP-ERROR-CODE
   TLV Error Code Field" in the "Path Computation Element Protocol(PCEP)
   Numbers" registry.

       Value      Meaning                     Reference
       ---       -----------------------     -----------
       TBD        SID Verification fails      This document

9.5.  PATH-SETUP-TYPE-CAPABILITY Sub-TLV Type Indicators

   IANA maintains a sub-registry, named "PATH-SETUP-TYPE-CAPABILITY Sub-
   TLV Type Indicators", within the "Path Computation Element Protocol
   (PCEP) Numbers" registry to manage the type indicator space for sub-
   TLVs of the PATH-SETUP-TYPE-CAPABILITY TLV.  IANA is requested to
   confirm the following allocations in the sub-registry.

      Value     Meaning                     Reference
      -----     -------                     ---------
      27        SRv6-PCE-CAPABILITY         This Document

9.6.  SRv6 PCE Capability Flags

   IANA is requested to create a new sub-registry, named "SRv6
   Capability Flag Field", within the "Path Computation Element Protocol
   (PCEP) Numbers" registry to manage the 16-bit Flag field of the SRv6-
   PCE-CAPABILITY sub-TLV.  New values are to be assigned by Standards
   Action [RFC8126].  Each bit should be tracked with the following
   qualities.

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

   *  Description

   *  Reference

   The following values are defined in this document.

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                    Bit     Description           Reference
                   -----   ------------------     --------------
                    0-13    Unassigned
                     14     Node or Adjacency     This document
                            Identifier (NAI) is
                            supported (N)
                     15     Unassigned

9.7.  New Path Setup Type

   [RFC8408] created a sub-registry within the "Path Computation Element
   Protocol (PCEP) Numbers" registry called "PCEP Path Setup Types".
   IANA is requested to confirm the following allocations in the sub-
   registry.

   Value             Description                  Reference
   -----             -----------                  ---------
   3                 Traffic engineering path is  This Document
                     setup using SRv6.

9.8.  ERROR Objects

   IANA is requested to confirm the following allocations in the PCEP-
   ERROR Object Error Types and Values registry for the following new
   error-values.

      Error-Type   Meaning
      ----------   -------
      10           Reception of an invalid object
                   Error-value = 34 (Missing
                   PCE-SRv6-CAPABILITY sub-TLV)
                   Error-value = 35 (Both SID and NAI are absent
                   in SRv6-RRO subobject)
                   Error-value = 36 (RRO mixes SRv6-RRO subobjects
                   with other subobject types)
                   Error-value = 37 (Invalid SRv6 SID Structure)
      19           Invalid Operation
                   Error-value = 19 (Attempted SRv6 when the
                   capability was not advertised)

   IANA is requested to make new allocations in the PCEP-ERROR Object
   Error Types and Values registry for the following new error-values.

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      Error-Type   Meaning
      ----------   -------
      10           Reception of an invalid object
                   Error-value = TBD (Unsupported number of
                   SRv6-ERO subobjects)
                   Error-value = TBD (Unsupported NAI Type
                   in the SRv6-ERO/SRv6-RRO subobject)
                   Error-value = TBD (Both SID and NAI are
                   absent in the SRv6-ERO subobject)
                   Error-value = TBD (ERO mixes SRv6-ERO
                   subobjects with other subobject types)
                   Error-value = TBD (Unsupported number
                   of SRv6-ERO subobjects)

10.  References

10.1.  Normative References

   [RFC3209]  Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
              and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
              Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001,
              <https://www.rfc-editor.org/rfc/rfc3209>.

   [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/rfc/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/rfc/rfc8126>.

   [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/rfc/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/rfc/rfc8281>.

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   [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/rfc/rfc8408>.

   [RFC8491]  Tantsura, J., Chunduri, U., Aldrin, S., and L. Ginsberg,
              "Signaling Maximum SID Depth (MSD) Using IS-IS", RFC 8491,
              DOI 10.17487/RFC8491, November 2018,
              <https://www.rfc-editor.org/rfc/rfc8491>.

   [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/rfc/rfc8253>.

   [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/rfc/rfc8664>.

   [RFC8986]  Filsfils, C., Ed., Camarillo, P., Ed., Leddy, J., Voyer,
              D., Matsushima, S., and Z. Li, "Segment Routing over IPv6
              (SRv6) Network Programming", RFC 8986,
              DOI 10.17487/RFC8986, February 2021,
              <https://www.rfc-editor.org/rfc/rfc8986>.

   [RFC9514]  Dawra, G., Filsfils, C., Talaulikar, K., Ed., Chen, M.,
              Bernier, D., and B. Decraene, "Border Gateway Protocol -
              Link State (BGP-LS) Extensions for Segment Routing over
              IPv6 (SRv6)", RFC 9514, DOI 10.17487/RFC9514, December
              2023, <https://www.rfc-editor.org/rfc/rfc9514>.

   [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/rfc/rfc2119>.

   [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/rfc/rfc8174>.

10.2.  Informative References

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   [RFC4657]  Ash, J., Ed. and J.L. Le Roux, Ed., "Path Computation
              Element (PCE) Communication Protocol Generic
              Requirements", RFC 4657, DOI 10.17487/RFC4657, September
              2006, <https://www.rfc-editor.org/rfc/rfc4657>.

   [RFC6952]  Jethanandani, M., Patel, K., and L. Zheng, "Analysis of
              BGP, LDP, PCEP, and MSDP Issues According to the Keying
              and Authentication for Routing Protocols (KARP) Design
              Guide", RFC 6952, DOI 10.17487/RFC6952, May 2013,
              <https://www.rfc-editor.org/rfc/rfc6952>.

   [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/rfc/rfc7942>.

   [RFC8051]  Zhang, X., Ed. and I. Minei, Ed., "Applicability of a
              Stateful Path Computation Element (PCE)", RFC 8051,
              DOI 10.17487/RFC8051, January 2017,
              <https://www.rfc-editor.org/rfc/rfc8051>.

   [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/rfc/rfc8402>.

   [RFC8754]  Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J.,
              Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
              (SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020,
              <https://www.rfc-editor.org/rfc/rfc8754>.

   [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/rfc/rfc9256>.

   [RFC9352]  Psenak, P., Ed., Filsfils, C., Bashandy, A., Decraene, B.,
              and Z. Hu, "IS-IS Extensions to Support Segment Routing
              over the IPv6 Data Plane", RFC 9352, DOI 10.17487/RFC9352,
              February 2023, <https://www.rfc-editor.org/rfc/rfc9352>.

   [I-D.ietf-pce-pcep-yang]
              Dhody, D., Beeram, V. P., Hardwick, J., and J. Tantsura,
              "A YANG Data Model for Path Computation Element
              Communications Protocol (PCEP)", Work in Progress,
              Internet-Draft, draft-ietf-pce-pcep-yang-23, 18 March
              2024, <https://datatracker.ietf.org/doc/html/draft-ietf-
              pce-pcep-yang-23>.

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   [I-D.ietf-pce-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-05, 18 March
              2024, <https://datatracker.ietf.org/doc/html/draft-ietf-
              pce-pcep-srv6-yang-05>.

Acknowledgements

   The authors would like to thank Jeff Tantsura, Adrian Farrel, Aijun
   Wang, Khasanov Boris, Ketan Talaulikar, Martin Vigoureux, Hariharan
   Ananthakrishnan, Xinyue Zhang, John Scudder, Julien Meuric and Robert
   Varga for valuable suggestions.

   Thanks to Gunter Van de Velde, Eric Vyncke, Jim Guichard, and Mahesh
   Jethanandani for their comments during the IESG review.

Contributors

   Mahendra Singh Negi
   RtBrick Inc
   Bangalore
   Karnataka
   India
   Email: mahend.ietf@gmail.com

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

   Huang Wumin
   Huawei Technologies
   Huawei Building, No. 156 Beiqing Rd.
   Beijing
   100095
   China
   Email: huangwumin@huawei.com

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

   Ran Chen
   ZTE Corporation
   China
   Email: chen.ran@zte.com.cn

Authors' Addresses

   Cheng Li(Editor)
   Huawei Technologies
   Huawei Campus, No. 156 Beiqing Rd.
   Beijing
   100095
   China
   Email: c.l@huawei.com

   Prejeeth Kaladharan
   RtBrick Inc
   Bangalore
   Karnataka
   India
   Email: prejeeth@rtbrick.com

   Siva Sivabalan
   Ciena Corporation
   Email: msiva282@gmail.com

   Mike Koldychev
   Cisco Systems, Inc.
   Canada
   Email: mkoldych@cisco.com

   Yongqing Zhu
   China Telecom
   109 West Zhongshan Ave, Tianhe District

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   Bangalore
   Guangzhou,
   P.R. China
   Email: zhuyq8@chinatelecom.cn

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