    Internet Engineering Task Force (IETF)                          U. Palle
    Request for Comments: 8623                                      D. Dhody
    Category: Standards Track                            Huawei Technologies
    ISSN: 2070-1721                                                Y. Tanaka
                                                          NTT Communications
                                                                   V. Beeram
                                                            Juniper Networks
                                                                   June 2019

          Stateful Path Computation Element (PCE) Protocol Extensions
       for Usage with Point-to-Multipoint TE Label Switched Paths (LSPs)

    Abstract

       The Path Computation Element (PCE) has been identified as an
       appropriate technology for the determination of the paths of point-
       to-multipoint (P2MP) TE Label Switched Paths (LSPs).  This document
       provides extensions required for the Path Computation Element
       Communication Protocol (PCEP) so as to enable the usage of a stateful
       PCE capability in supporting P2MP TE LSPs.

    Status of This Memo

       This is an Internet Standards Track document.

       This document is a product of the Internet Engineering Task Force
       (IETF).  It represents the consensus of the IETF community.  It has
       received public review and has been approved for publication by the
       Internet Engineering Steering Group (IESG).  Further information on
       Internet Standards is available in Section 2 of RFC 7841.

       Information about the current status of this document, any errata,
       and how to provide feedback on it may be obtained at
       https://www.rfc-editor.org/info/rfc8623.

    Palle, et al.                Standards Track                    [Page 1]

    RFC 8623                      Stateful P2MP                    June 2019

    Copyright Notice

       Copyright (c) 2019 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 Simplified BSD License text as described in Section 4.e of
       the Trust Legal Provisions and are provided without warranty as
       described in the Simplified BSD License.

    Table of Contents

       1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
         1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   4
       2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
       3.  Supporting P2MP TE LSPs for Stateful PCE  . . . . . . . . . .   4
         3.1.  Motivation  . . . . . . . . . . . . . . . . . . . . . . .   4
         3.2.  Objectives  . . . . . . . . . . . . . . . . . . . . . . .   5
       4.  Functions to Support P2MP TE LSPs for Stateful PCEs . . . . .   5
       5.  Architectural Overview of Protocol Extensions . . . . . . . .   6
         5.1.  Extension of PCEP Messages  . . . . . . . . . . . . . . .   6
         5.2.  Capability Advertisement  . . . . . . . . . . . . . . . .   7
         5.3.  IGP Extensions for Stateful PCE P2MP Capabilities
               Advertisement . . . . . . . . . . . . . . . . . . . . . .   7
         5.4.  State Synchronization . . . . . . . . . . . . . . . . . .   8
         5.5.  LSP Delegation  . . . . . . . . . . . . . . . . . . . . .   8
         5.6.  LSP Operations  . . . . . . . . . . . . . . . . . . . . .   9
           5.6.1.  Passive Stateful PCE  . . . . . . . . . . . . . . . .   9
           5.6.2.  Active Stateful PCE . . . . . . . . . . . . . . . . .   9
           5.6.3.  PCE-Initiated LSP . . . . . . . . . . . . . . . . . .   9
             5.6.3.1.  P2MP TE LSPs Instantiation  . . . . . . . . . . .   9
             5.6.3.2.  P2MP TE LSPs Deletion . . . . . . . . . . . . . .  10
             5.6.3.3.  Adding and Pruning Leaves for the P2MP TE LSP . .  10
             5.6.3.4.  P2MP TE LSPs Delegation and Cleanup . . . . . . .  10
       6.  PCEP Message Extensions . . . . . . . . . . . . . . . . . . .  11
         6.1.  The PCRpt Message . . . . . . . . . . . . . . . . . . . .  11
         6.2.  The PCUpd Message . . . . . . . . . . . . . . . . . . . .  13
         6.3.  The PCReq Message . . . . . . . . . . . . . . . . . . . .  14
         6.4.  The PCRep Message . . . . . . . . . . . . . . . . . . . .  15
         6.5.  The PCInitiate Message  . . . . . . . . . . . . . . . . .  16
         6.6.  Example . . . . . . . . . . . . . . . . . . . . . . . . .  17

    Palle, et al.                Standards Track                    [Page 2]

    RFC 8623                      Stateful P2MP                    June 2019

           6.6.1.  P2MP TE LSPs Update Request . . . . . . . . . . . . .  17
           6.6.2.  P2MP TE LSP Report  . . . . . . . . . . . . . . . . .  17
           6.6.3.  P2MP TE LSPs Initiation Request . . . . . . . . . . .  18
       7.  PCEP Object Extensions  . . . . . . . . . . . . . . . . . . .  19
         7.1.  LSP Object Extension  . . . . . . . . . . . . . . . . . .  19
           7.1.1.  P2MP-LSP-IDENTIFIERS TLV  . . . . . . . . . . . . . .  19
         7.2.  S2LS Object . . . . . . . . . . . . . . . . . . . . . . .  22
       8.  Message Fragmentation . . . . . . . . . . . . . . . . . . . .  23
         8.1.  Report Fragmentation Procedure  . . . . . . . . . . . . .  23
         8.2.  Update Fragmentation Procedure  . . . . . . . . . . . . .  23
         8.3.  PCInitiate Fragmentation Procedure  . . . . . . . . . . .  24
       9.  Nonsupport of P2MP TE LSPs for Stateful PCE . . . . . . . . .  24
       10. Manageability Considerations  . . . . . . . . . . . . . . . .  25
         10.1.  Control of Function and Policy . . . . . . . . . . . . .  25
         10.2.  Information and Data Models  . . . . . . . . . . . . . .  25
         10.3.  Liveness Detection and Monitoring  . . . . . . . . . . .  25
         10.4.  Verify Correct Operations  . . . . . . . . . . . . . . .  26
         10.5.  Requirements on Other Protocols  . . . . . . . . . . . .  26
         10.6.  Impact on Network Operations . . . . . . . . . . . . . .  26
       11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  26
         11.1.  PCE Capabilities in IGP Advertisements . . . . . . . . .  26
         11.2.  STATEFUL-PCE-CAPABILITY TLV  . . . . . . . . . . . . . .  26
         11.3.  LSP Object . . . . . . . . . . . . . . . . . . . . . . .  27
         11.4.  PCEP-ERROR Object  . . . . . . . . . . . . . . . . . . .  27
         11.5.  PCEP TLV Type Indicators . . . . . . . . . . . . . . . .  28
         11.6.  PCEP Object  . . . . . . . . . . . . . . . . . . . . . .  28
         11.7.  S2LS Object  . . . . . . . . . . . . . . . . . . . . . .  28
       12. Security Considerations . . . . . . . . . . . . . . . . . . .  29
       13. References  . . . . . . . . . . . . . . . . . . . . . . . . .  29
         13.1.  Normative References . . . . . . . . . . . . . . . . . .  29
         13.2.  Informative References . . . . . . . . . . . . . . . . .  31
       Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  32
       Contributors  . . . . . . . . . . . . . . . . . . . . . . . . . .  32
       Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  33

    1.  Introduction

       As per [RFC4655], the Path Computation Element (PCE) is an entity
       that is capable of computing a network path or route based on a
       network graph and applying computational constraints.  A Path
       Computation Client (PCC) may make requests to a PCE for paths to be
       computed.

       [RFC4875] describes how to set up point-to-multipoint (P2MP) Traffic
       Engineering Label Switched Paths (TE LSPs) for use in Multiprotocol
       Label Switching (MPLS) and Generalized MPLS (GMPLS) networks.
       [RFC5671] examines the applicability of PCE for the path computation
       for P2MP TE LSPs.

    Palle, et al.                Standards Track                    [Page 3]

    RFC 8623                      Stateful P2MP                    June 2019

       The PCEP is designed as a communication protocol between PCCs and
       PCEs for point-to-point (P2P) path computations and is defined in
       [RFC5440].  The extensions of PCEP to request path computation for
       P2MP TE LSPs are described in [RFC8306].

       Stateful PCEs are shown to be helpful in many application scenarios,
       in both MPLS and GMPLS networks, as illustrated in [RFC8051].  These
       scenarios apply equally to P2P and P2MP TE LSPs.  [RFC8231] provides
       the fundamental extensions to PCEP needed for stateful PCE to support
       general functionality for P2P TE LSP.  [RFC8281] provides extensions
       to PCEP needed for stateful PCE-initiated P2P TE LSP.  This document
       complements that work by focusing on PCEP extensions that are
       necessary in order for the deployment of stateful PCEs to support
       P2MP TE LSPs.  This document describes the setup, maintenance, and
       teardown of PCE-initiated P2MP LSPs under the stateful PCE model.

    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

       Terminology used in this document is the same as terminology used in
       [RFC8231], [RFC8281], and [RFC8306].

    3.  Supporting P2MP TE LSPs for Stateful PCE

    3.1.  Motivation

       [RFC8051] presents several use cases, demonstrating scenarios that
       benefit from the deployment of a stateful PCE including optimization,
       recovery, etc., which are equally applicable to P2MP TE LSPs.
       [RFC8231] defines the extensions to PCEP needed for stateful
       operation of P2P TE LSPs.  This document complements the previous
       work by focusing on extensions that are necessary in order for the
       deployment of stateful PCEs to support P2MP TE LSPs.

       In addition to that, the stateful nature of a PCE simplifies the
       information conveyed in PCEP messages since it is possible to refer
       to the LSPs via a PCEP-specific LSP identifier (PLSP-ID) ([RFC8231]).
       For P2MP, where the size of the message is much larger, this is an
       added advantage.  When using a stateless PCE, a request to modify an
       existing P2MP tree requires that all the leaves are presented in the
       PCEP messages along with all the path information.  But when using a

    Palle, et al.                Standards Track                    [Page 4]

    RFC 8623                      Stateful P2MP                    June 2019

       stateful PCE, the PCEP messages can use a PLSP-ID to represent all
       information about the LSP that has previously been exchanged in PCEP
       messages, and it is only necessary to encode the modifications (such
       as new or removed leaf nodes).  The PLSP-ID provides an index into
       the LSP-DB at the PCE and identifies the LSP at the PCC.

       In environments where the P2MP TE LSPs placement needs to change in
       response to application demands, it is useful to support dynamic
       creation and tear down of P2MP TE LSPs.  The ability for a PCE to
       trigger the creation of P2MP TE LSPs on demand can be seamlessly
       integrated into a controller-based network architecture where
       intelligence in the controller can determine when and where to set up
       paths.  Section 3 of [RFC8281] further describes the motivation
       behind the PCE-Initiation capability, which is equally applicable to
       P2MP TE LSPs.

    3.2.  Objectives

       The objectives for the protocol extensions to support P2MP TE LSPs
       for stateful PCE are the same as the objectives described in
       Section 3.2 of [RFC8231].

    4.  Functions to Support P2MP TE LSPs for Stateful PCEs

       [RFC8231] specifies new functions to support a stateful PCE.  It also
       specifies that a function can be initiated either from a PCC towards
       a PCE (C-E) or from a PCE towards a PCC (E-C).

       This document extends these functions to support P2MP TE LSPs:

       Capability Advertisement (E-C,C-E):  Both the PCC and the PCE must
          announce during PCEP session establishment that they support
          Stateful PCE extensions for P2MP using mechanisms defined in
          Section 5.2.

       LSP State Synchronization (C-E):  After the session between the PCC
          and a stateful PCE with P2MP capability is initialized, the PCE
          must learn the state of a PCC's P2MP TE LSPs before it can perform
          path computations or update LSP attributes in a PCC.

       LSP Update Request (E-C):  A stateful PCE with P2MP capability
          requests modification of attributes on a PCC's P2MP TE LSPs.

       LSP State Report (C-E):  A PCC sends an LSP state report to a PCE
          whenever the state of a P2MP TE LSP changes.

    Palle, et al.                Standards Track                    [Page 5]

    RFC 8623                      Stateful P2MP                    June 2019

       LSP Control Delegation (C-E,E-C):  A PCC grants to a PCE the right to
          update LSP attributes on one or more P2MP TE LSPs; the PCE becomes
          the authoritative source of the LSP's attributes as long as the
          delegation is in effect (See Section 5.7 of [RFC8231]); the PCC
          may withdraw the delegation or the PCE may give up the delegation
          at any time.

       PCE-initiated LSP instantiation (E-C):  A PCE sends an LSP Initiate
          Message to a PCC to instantiate or delete a P2MP TE LSP [RFC8281].

    5.  Architectural Overview of Protocol Extensions

    5.1.  Extension of PCEP Messages

       Two new PCEP messages are defined in [RFC8231] to support stateful
       PCE for P2P TE LSPs.  In this document, these messages are extended
       as follows to support P2MP TE LSPs.

       Path Computation State Report (PCRpt):  Each P2MP TE LSP State Report
          in a PCRpt message contains the actual P2MP TE LSP path
          attributes, the LSP status, etc.  An LSP State Report carried in a
          PCRpt message is also used in delegation or revocation of control
          of a P2MP TE LSP to/from a PCE.  The extension of PCRpt messages
          is described in Section 6.1.

       Path Computation Update Request (PCUpd):  Each P2MP TE LSP Update
          Request in a PCUpd message MUST contain all LSP parameters that a
          PCE wishes to set for a given P2MP TE LSP.  An LSP Update Request
          carried in a PCUpd message is also used to return LSP delegations
          if at any point the PCE no longer desires control of a P2MP TE
          LSP.  The PCUpd message is described in Section 6.2.

       Further, a new PCEP message is defined in [RFC8281] to support
       stateful PCE instantiation of P2P TE LSPs.  In this document, this
       message is extended as follows to support P2MP TE LSPs.

       Path Computation LSP Initiate Message (PCInitiate):  PCInitiate is a
          PCEP message sent by a PCE to a PCC to trigger the instantiation
          or deletion of a P2MP TE LSP.  The PCInitiate message is described
          in Section 6.5.

       The Path Computation Request (PCReq) and Path Computation Reply
       (PCRep) messages are also extended to support passive stateful PCE
       for P2P TE LSPs in [RFC8231].  In this document, these messages are
       extended to support P2MP TE LSPs as well.

    Palle, et al.                Standards Track                    [Page 6]

    RFC 8623                      Stateful P2MP                    June 2019

    5.2.  Capability Advertisement

       During the PCEP initialization phase, as per Section 7.1.1 of
       [RFC8231], PCEP speakers advertise Stateful capability via the
       STATEFUL-PCE-CAPABILITY TLV in the OPEN object.  Various flags are
       defined for the STATEFUL-PCE-CAPABILITY TLV defined in [RFC8231] and
       updated in [RFC8281] and [RFC8232].

       Three new flags, N (P2MP-CAPABILITY), M (P2MP-LSP-UPDATE-CAPABILITY),
       and P (P2MP-LSP-INSTANTIATION-CAPABILITY), are added in this
       document:

       N (P2MP-CAPABILITY flag - 1 bit):  If set to 1 by a PCC, the N Flag
          indicates that the PCC is willing to send P2MP LSP State Reports
          whenever there's a change to the parameters or operational status
          of the P2MP LSP; if set to 1 by a PCE, the N Flag indicates that
          the PCE is interested in receiving LSP State Reports whenever
          there is a parameter or operational status change to the P2MP LSP.
          The P2MP-CAPABILITY Flag MUST be advertised by both a PCC and a
          PCE for the P2MP extension (as per this document) of the PCRpt
          messages to be allowed on a PCEP session.

       M (P2MP-LSP-UPDATE-CAPABILITY flag - 1 bit):  If set to 1 by a PCC,
          the M Flag indicates that the PCC allows modification of P2MP LSP
          parameters; if set to 1 by a PCE, the M Flag indicates that the
          PCE is capable of updating P2MP LSP parameters.  The P2MP-LSP-
          UPDATE-CAPABILITY Flag MUST be advertised by both a PCC and a PCE
          for the P2MP extension (as per this document) of the PCUpd
          messages to be allowed on a PCEP session.

       P (P2MP-LSP-INSTANTIATION-CAPABILITY flag - 1 bit):  If set to 1 by a
          PCC, the P Flag indicates that the PCC allows instantiation of a
          P2MP LSP by a PCE.  If set to 1 by a PCE, the P flag indicates
          that the PCE supports P2MP LSP instantiation.  The P2MP-LSP-
          INSTANTIATION-CAPABILITY flag MUST be set by both PCC and PCE in
          order to support PCE-initiated P2MP LSP instantiation.

       A PCEP speaker should continue to advertise the basic P2MP capability
       via mechanisms as described in [RFC8306].

    5.3.  IGP Extensions for Stateful PCE P2MP Capabilities Advertisement

       When the PCC is a Label Switching Router (LSR) participating in the
       IGP (either OSPF or IS-IS), and PCEs are either LSRs or servers also
       participating in the IGP, an effective mechanism for PCE discovery
       within an IGP routing domain consists of utilizing IGP

    Palle, et al.                Standards Track                    [Page 7]

    RFC 8623                      Stateful P2MP                    June 2019

       advertisements.  Extensions for the advertisement of PCE discovery
       information are defined for OSPF and for IS-IS in [RFC5088] and
       [RFC5089], respectively.

       The PCE-CAP-FLAGS sub-TLV, defined in [RFC5089], is an optional sub-
       TLV used to advertise PCE capabilities.  It MAY be present within the
       PCE Discovery (PCED) TLV carried by OSPF or IS-IS.  [RFC5088] and
       [RFC5089] provide the description and processing rules for this sub-
       TLV when carried within OSPF and IS-IS, respectively.

       The format of the PCE-CAP-FLAGS sub-TLV is included below for easy
       reference:

       Type: 5

       Length: Multiple of 4

       Value: This contains an array of units of 32-bit flags with the most
       significant bit as 0.  Each bit represents one PCE capability.

       PCE capability bit flags are defined in [RFC5088].  This document
       defines new capability bits for the stateful PCE with P2MP as
       follows:

                   Bit                  Capability
                   13                   Active Stateful PCE with P2MP
                   14                   Passive Stateful PCE with P2MP
                   15                   PCE-Initiation with P2MP

       Note that, while active, passive, or initiation stateful PCE
       capabilities for P2MP may be advertised during discovery, PCEP
       Speakers that wish to use stateful PCEP for P2MP TE LSPs MUST
       advertise stateful PCEP capabilities during PCEP session setup, as
       specified in the current document.  A PCC MAY initiate stateful PCEP
       P2MP capability advertisement at PCEP session setup even if it did
       not receive any IGP PCE capability advertisements.

    5.4.  State Synchronization

       State Synchronization operations (described in Section 5.6 of
       [RFC8231]) are applicable for the P2MP TE LSPs as well.  The
       optimizations described in [RFC8232] can also be applied for P2MP TE
       LSPs.

    5.5.  LSP Delegation

       LSP delegation operations (described in Section 5.7 of [RFC8231]) are
       applicable for P2MP TE LSPs as well.

    Palle, et al.                Standards Track                    [Page 8]

    RFC 8623                      Stateful P2MP                    June 2019

    5.6.  LSP Operations

    5.6.1.  Passive Stateful PCE

       LSP operations for passive stateful PCE (described in Section 5.8.1
       of [RFC8231]) are applicable for P2MP TE LSPs as well.

       The PCReq and PCRep message format for P2MP TE LSPs is described in
       Sections 3.4 and 3.5 of [RFC8306], respectively.

       The PCReq and PCRep message for P2MP TE LSPs are extended to support
       encoding of the LSP object so that it is possible to refer to an LSP
       with a unique identifier and simplify the PCEP message exchange.  For
       example, in case of modification of one leaf in a P2MP tree, there
       should be no need to carry the full P2MP tree in a PCReq message.

       The extensions for the Request and Response message for passive
       stateful operations on P2MP TE LSPs are described in Sections 6.3 and
       6.4.  The extension for the Path Computation LSP State Report (PCRpt)
       message is described in Section 6.1.

    5.6.2.  Active Stateful PCE

       LSP operations for active stateful PCE (described in Section 5.8.2 of
       [RFC8231]) are applicable for P2MP TE LSPs as well.

       The extension for the Path Computation LSP Update (PCUpd) message for
       active stateful operations on P2MP TE LSPs is described in
       Section 6.2.

    5.6.3.  PCE-Initiated LSP

       As per Section 5.1 of [RFC8281], the PCE sends a Path Computation LSP
       Initiate Request (PCInitiate) message to the PCC to suggest
       instantiation or deletion of a P2P TE LSP.  This document extends the
       PCInitiate message to support P2MP TE LSPs (see details in
       Section 6.5).

       The instantiation and deletion operations for P2MP TE LSPs are the
       same as for P2P LSPs as described in Sections 5.3 and 5.4 of
       [RFC8281].

    5.6.3.1.  P2MP TE LSPs Instantiation

       The instantiation operation of P2MP TE LSPs is the same as the LSP
       instantiation operation defined in Section 5.3 of [RFC8281]; this
       includes the handling of the PLSP-ID, SYMBOLIC-PATH-NAME TLV, etc.
       The processing rules and use of error codes remain unchanged.  The N

    Palle, et al.                Standards Track                    [Page 9]

    RFC 8623                      Stateful P2MP                    June 2019

       (P2MP) flag (Section 7.1) MUST be set in the LSP object in the
       PCInitiate message by the PCE to specify that the instantiation is
       for P2MP TE LSPs.  Like the PLSP-ID (as per [RFC8281]), the P2MP-LSP-
       IDENTIFIERS TLV SHOULD NOT be included in the LSP object in
       PCInitiate messages and MUST be ignored on receipt.  These
       identifiers are generated by the PCC on receipt of the PCInitiate
       message and reported via a PCRpt message to the PCE.

    5.6.3.2.  P2MP TE LSPs Deletion

       The deletion operation of P2MP TE LSPs is the same as the LSP
       deletion operation defined in Section 5.4 of [RFC8281]; this entails
       sending an LSP Initiate Message with an LSP object carrying the PLSP-
       ID of the LSP to be removed as well as a Stateful PCE Request
       Parameter (SRP) object with the R flag set (LSP-REMOVE as per
       Section 5.2 of [RFC8281]).  The processing rules and error codes
       remain unchanged.

    5.6.3.3.  Adding and Pruning Leaves for the P2MP TE LSP

       The adding of new leaves and pruning of old leaves for the PCE-
       initiated P2MP TE LSP MUST be carried in a PCUpd message as per
       Section 6.2 for P2MP TE LSP extensions.  As defined in [RFC8306],
       leaf type = 1 is used for adding new leaves, and leaf type = 2 is
       used for pruning old leaves of P2MP END-POINTS Objects.

       PCC MAY use the Incremental State Update mechanism as described in
       [RFC4875] to signal the adding and pruning of leaves.

       Section 3.10 of [RFC8306] defines the error-handling procedures when
       adding new leaves to or removing old leaves from the existing P2MP
       tree for PCReq messages.  The same error handling and error codes are
       also applicable to the stateful PCE messages as described in this
       document.

    5.6.3.4.  P2MP TE LSPs Delegation and Cleanup

       P2MP TE LSPs delegation and cleanup operations are the same as the
       LSP delegation and cleanup operations defined in Section 6 of
       [RFC8281].  The processing rules and error codes remain unchanged.

    Palle, et al.                Standards Track                   [Page 10]

    RFC 8623                      Stateful P2MP                    June 2019

    6.  PCEP Message Extensions

       Message formats in this section, as those in [RFC8231], [RFC8281],
       and [RFC5440], are presented using Routing Backus-Naur Format (RBNF)
       as specified in [RFC5511].

    6.1.  The PCRpt Message

       As per Section 6.1 of [RFC8231], a PCRpt message is used to report
       the current state of a P2P TE LSP.  This document extends the PCRpt
       message in reporting the status of P2MP TE LSPs.

       The format of a PCRpt message is as follows:

       <PCRpt Message> ::= <Common Header>
                         <state-report-list>
       Where:

       <state-report-list> ::= <state-report>
                             [<state-report-list>]

       <state-report> ::= [<SRP>]
                           <LSP>
                           <path>

       Where:
       <path> ::= <end-point-intended-path-pair-list>
                  [<actual-attribute-list>
                  <end-point-actual-path-pair-list>]
                  [<intended-attribute-list>]

       <end-point-intended-path-pair-list>::=
                          [<END-POINTS>]
                          [<S2LS>]
                          <intended-path>
                          [<end-point-intended-path-pair-list>]

       <end-point-actual-path-pair-list>::=
                          [<END-POINTS>]
                          [<S2LS>]
                          <actual-path>
                          [<end-point-actual-path-pair-list>]

       <intended-path> ::= (<ERO>|<SERO>)
                  [<intended-path>]

       <actual-path> ::= (<RRO>|<SRRO>)
                  [<actual-path>]

    Palle, et al.                Standards Track                   [Page 11]

    RFC 8623                      Stateful P2MP                    June 2019

       <intended-attribute-list> is defined in [RFC5440] and extended by
       PCEP extensions.

       <actual-attribute-list> consists of the actual computed and signaled
       values of the <BANDWIDTH> and <metric-lists> objects defined in
       [RFC5440].

       The P2MP END-POINTS object defined in [RFC8306] is mandatory for
       specifying the address of P2MP leaves, grouped by leaf types.

       o  New leaves to add (leaf type = 1)

       o  Old leaves to remove (leaf type = 2)

       o  Old leaves whose path can be modified/reoptimized (leaf type = 3)

       o  Old leaves whose path must be left unchanged (leaf type = 4)

       When reporting the status of a P2MP TE LSP, the destinations MUST be
       grouped in the END-POINTS object based on the operational status (O
       field in S2LS objects) and leaf type (in END-POINTS objects).  This
       way, leaves of the same type that share the same operational status
       can be grouped together.  For reporting the status of delegated P2MP
       TE LSPs, leaf type = 3 is used, whereas for nondelegated P2MP TE
       LSPs, leaf type = 4 is used.

       For a delegated P2MP TE LSP, configuration changes are reported via a
       PCRpt message.  For example, for adding new leaves, leaf type = 1 is
       used in the END-POINTS object, and for removing old leaves, leaf type
       = 2 is used.

       Note that the compatibility with the [RFC8231] definition of <state-
       report> is preserved.  At least one instance of <END-POINTS> MUST be
       present in this message for P2MP LSP.

       Note that the ordering of <end-point-intended-path-pair-list>,
       <actual-attribute-list>, <end-point-actual-path-pair-list>, and
       <intended-attribute-list> is done to retain compatibility with state
       reports for the P2P LSPs as per [RFC8231].

       During state synchronization, the PCRpt message reports the status of
       the full P2MP tree.

       The S2LS object MUST be carried in a PCRpt message along with the
       END-POINTS object when an N (P2MP) flag is set in an LSP object for
       P2MP TE LSPs.  If the S2LS object is missing, the receiving PCE MUST
       send a PCEP Error (PCErr) message with Error-type=6 ("Mandatory
       Object missing") and Error-value=13 ("S2LS object missing").  If the

    Palle, et al.                Standards Track                   [Page 12]

    RFC 8623                      Stateful P2MP                    June 2019

       END-POINTS object is missing, the receiving PCE MUST send a PCErr
       message with Error-type=6 ("Mandatory Object missing") and Error-
       value=3 ("END-POINTS object missing") (defined in [RFC5440].

       The S2LS object could be used in conjunction with the intended-path
       (EXPLICIT_ROUTE object or ERO) as well as the actual-path
       (RECORD_ROUTE object or RRO); for the same leaf, the state encoded in
       the S2LS object associated with the actual-path MUST be used over the
       intended-path.

       If the E-bit (ERO-Compress bit) was set to 1 in the report, then the
       path will be formed by an ERO followed by a list of
       SECONDARY_EXPLICIT_ROUTE Objects (SEROs), or an RRO followed by a
       list of SECONDARY_RECORD_ROUTE Objects (SRROs).

    6.2.  The PCUpd Message

       As per Section 6.2 of [RFC8231], a PCUpd message is used to update
       P2P TE LSP attributes.  This document extends the PCUpd message in
       updating the attributes of a P2MP TE LSP.

       The format of a PCUpd message is as follows:

          <PCUpd Message> ::= <Common Header>
                              <update-request-list>

          Where:

          <update-request-list> ::= <update-request>
                                    [<update-request-list>]

          <update-request> ::= <SRP>
                               <LSP>
                               <path>

          Where:
          <path> ::= <end-point-path-pair-list>
                     <intended-attribute-list>

          <end-point-path-pair-list>::=
                          [<END-POINTS>]
                          <intended-path>
                          [<end-point-path-pair-list>]

          <intended-path> ::= (<ERO>|<SERO>)
                     [<intended-path>]

    Palle, et al.                Standards Track                   [Page 13]

    RFC 8623                      Stateful P2MP                    June 2019

       <intended-attribute-list> is the attribute-list defined in [RFC5440]
       and extended by PCEP extensions.

       Note that the compatibility with the [RFC8231] definition of <update-
       request> is preserved.

       The PCC SHOULD use the make-before-break or sub-group-based
       procedures described in [RFC4875] based on a local policy decision.

       The END-POINTS object MUST be carried in a PCUpd message when the N
       flag is set in the LSP object for a P2MP TE LSP.  If the END-POINTS
       object is missing, the receiving PCC MUST send a PCErr message with
       Error-type=6 ("Mandatory Object missing") and Error-value=3
       ("END-POINTS object missing") (defined in [RFC5440]).

    6.3.  The PCReq Message

       As per Section 3.4 of [RFC8306], a PCReq message is used for a P2MP
       Path Computation Request.  This document extends the PCReq message
       such that a PCC MAY include the LSP object in the PCReq message if
       the stateful PCE P2MP capability has been negotiated on a PCEP
       session between the PCC and a PCE.

       The format of a PCReq message is as follows:

        <PCReq Message>::= <Common Header>
                           [<svec-list>]
                           <request-list>

       where:

       <svec-list>::= <SVEC>
                      [<OF>]
                      [<metric-list>]
                      [<svec-list>]

       <request-list>::=<request>[<request-list>]

       <request>::= <RP>
                    <end-point-rro-pair-list>
                    [<LSP>]
                    [<OF>]
                    [<LSPA>]
                    [<BANDWIDTH>]
                    [<metric-list>]
                    [<IRO>|<BNC>]
                    [<LOAD-BALANCING>]

    Palle, et al.                Standards Track                   [Page 14]

    RFC 8623                      Stateful P2MP                    June 2019

       <end-point-rro-pair-list>::= <END-POINTS>
                                    [<RRO-List>[<BANDWIDTH>]]
                                    [<end-point-rro-pair-list>]

       <RRO-List>::=(<RRO>|<SRRO>)[<RRO-List>]
       <metric-list>::=<METRIC>[<metric-list>]

    6.4.  The PCRep Message

       As per Section 3.5 of [RFC8306], a PCRep message is used for a P2MP
       Path Computation Reply.  This document extends the PCRep message such
       that a PCE MAY include the LSP object in the PCRep message if the
       stateful PCE P2MP capability has been negotiated on a PCEP session
       between the PCC and a PCE.

       The format of a PCRep message is as follows:

       <PCRep Message>::= <Common Header>
                          <response-list>

       where:

       <response-list>::=<response>[<response-list>]

       <response>::=<RP>
                    [<end-point-path-pair-list>]
                    [<LSP>]
                    [<NO-PATH>]
                    [<UNREACH-DESTINATION>]
                    [<attribute-list>]

       <end-point-path-pair-list>::= [<END-POINTS>]
                                     <path>
                                     [<end-point-path-pair-list>]

       <path> ::= (<ERO>|<SERO>) [<path>]

       <attribute-list>::=[<OF>]
                          [<LSPA>]
                          [<BANDWIDTH>]
                          [<metric-list>]
                          [<IRO>]

    Palle, et al.                Standards Track                   [Page 15]

    RFC 8623                      Stateful P2MP                    June 2019

    6.5.  The PCInitiate Message

       As defined in section 5.1 of [RFC8281], a PCE sends a PCInitiate
       message to a PCC to recommend instantiation of a P2P TE LSP.  This
       document extends the format of a PCInitiate message for the creation
       of P2MP TE LSPs, but the creation and deletion operations of P2MP TE
       LSPs are the same to the P2P TE LSPs.

       The format of a PCInitiate message is as follows:

       <PCInitiate Message> ::= <Common Header>
                                <PCE-initiated-lsp-list>
       Where:

       <PCE-initiated-lsp-list> ::= <PCE-initiated-lsp-request>
                                    [<PCE-initiated-lsp-list>]

       <PCE-initiated-lsp-request> ::=
       (<PCE-initiated-lsp-instantiation>|<PCE-initiated-lsp-deletion>)

       <PCE-initiated-lsp-instantiation> ::= <SRP>
                                             <LSP>
                                             <end-point-path-pair-list>
                                             [<attribute-list>]

       <PCE-initiated-lsp-deletion> ::= <SRP>
                                        <LSP>

       Where:

       <end-point-path-pair-list>::=
                          [<END-POINTS>]
                          <intended-path>
                          [<end-point-path-pair-list>]

       <intended-path> ::= (<ERO>|<SERO>)
                  [<intended-path>]

       <attribute-list> is defined in [RFC5440] and extended by PCEP
       extensions.

       The PCInitiate message with an LSP object with the N flag (P2MP) set
       is used to convey operation on a P2MP TE LSP.  The SRP object is used
       to correlate between initiation requests sent by the PCE, and the
       error reports and state reports sent by the PCC as described in
       [RFC8231].

    Palle, et al.                Standards Track                   [Page 16]

    RFC 8623                      Stateful P2MP                    June 2019

       The END-POINTS object MUST be carried in a PCInitiate message when
       the N flag is set in an LSP object for a P2MP TE LSP.  If the END-
       POINTS object is missing, the receiving PCC MUST send a PCErr message
       with Error-type=6 ("Mandatory Object missing") and Error-value=3
       ("END-POINTS object missing") (defined in [RFC5440]).

    6.6.  Example

    6.6.1.  P2MP TE LSPs Update Request

       An LSP Update Request message is sent by an active stateful PCE to
       update the P2MP TE LSPs parameters or attributes.  An example of a
       PCUpd message for P2MP TE LSPs is described below:

                  Common Header
                  SRP
                  LSP with P2MP flag set
                  END-POINTS for leaf type 3
                    ERO list

       In this example, a stateful PCE requests an update of the path taken
       to some of the leaves in a P2MP tree.  The update request uses the
       END-POINT type 3 (modified/reoptimized).  The ERO list represents the
       source-to-leaves path after modification.  The update message does
       not need to encode the full P2MP tree in this case.

    6.6.2.  P2MP TE LSP Report

       The LSP State Report message is sent by a PCC to report or delegate
       the P2MP TE LSP.  The leaves of the P2MP TE LSP are grouped in the
       END-POINTS object based on the operational status and the leaf type.
       An example of a PCRpt message is described below for a delegated P2MP
       TE LSP to add new leaves to an existing P2MP TE LSP:

                  Common Header
                  LSP with P2MP flag set
                  END-POINTS for leaf type 1 (add)
                    S2LS (O=DOWN)
                    ERO list (empty)

       An example of a PCRpt message for a P2MP TE LSP is described below to
       prune leaves from an existing P2MP TE LSP:

                  Common Header
                  LSP with P2MP flag set
                  END-POINTS for leaf type 2 (remove)
                    S2LS (O=UP)
                    ERO list (empty)

    Palle, et al.                Standards Track                   [Page 17]

    RFC 8623                      Stateful P2MP                    June 2019

       An example of a PCRpt message for a delegated P2MP TE LSP is
       described below to report the status of leaves in an existing P2MP TE
       LSP:

                  Common Header
                  SRP
                  LSP with P2MP flag set
                  END-POINTS for leaf type 3 (modify)
                    S2LS (O=UP)
                    RRO list
                  END-POINTS for leaf type 3 (modify)
                    S2LS (O=DOWN)
                    ERO list (empty)

       In this example, the PCRpt message is in response to a PCUpd message.
       The PCRpt message includes the corresponding SRP object and indicates
       that some leaves are up (with the actual path) and some are down.

       An example of a PCRpt message for a nondelegated P2MP TE LSP is
       described below to report status of leaves:

                  Common Header
                  LSP with P2MP flag set
                  END-POINTS for leaf type 4 (unchanged)
                    S2LS (O=ACTIVE)
                    RRO list
                  END-POINTS for leaf type 4 (unchanged)
                    S2LS (O=DOWN)
                    ERO list (empty)

    6.6.3.  P2MP TE LSPs Initiation Request

       An LSP Initiation Request message is sent by a stateful PCE to create
       a P2MP TE LSP.  An example of a PCInitiate message for a P2MP TE LSP
       is described below:

                  Common Header
                  SRP
                  LSP with P2MP flag set
                  END-POINTS for leaf type 1 (add)
                    ERO list

       In this example, a stateful PCE requests the creation of a P2MP TE
       LSP.  The initiation request uses the END-POINT type 1 (new leaves).
       The ERO list represents the source-to-leaves path.  The initiate
       message encodes the full P2MP tree in this case.

    Palle, et al.                Standards Track                   [Page 18]

    RFC 8623                      Stateful P2MP                    June 2019

    7.  PCEP Object Extensions

       The new PCEP TLVs defined in this document are in compliance with the
       PCEP TLV format defined in [RFC5440].

    7.1.  LSP Object Extension

       The LSP Object is defined in Section 7.3 of [RFC8231].  It specifies
       the PLSP-ID to uniquely identify an LSP that is constant for the life
       time of a PCEP session.  Similarly, for a P2MP tunnel, the PLSP-ID
       uniquely identifies a P2MP TE LSP.  This document adds the following
       flags to the LSP Object:

       N (P2MP flag - 1 bit):  If the N flag is set to 1, it indicates that
          the message is for a P2MP TE LSP.

       F (Fragmentation flag - 1 bit):  If the F flag is unset (0), it
          indicates that the LSP is not fragmented or that it is the last
          piece of the fragmented LSP.  If the F flag is set to 1, it
          indicates that the LSP is fragmented and that it is not the last
          piece of the fragmented LSP.  The receiver needs to wait for
          additional fragments until it receives an LSP with the same PLSP-
          ID and with the F-bit set to 0.  See Section 8 for further
          details.

       E (ERO-compression flag - 1 bit):  If the E flag is set to 1, it
          indicates the route is in compressed format (that is, Secondary
          Explicit Route Object (SERO) and Secondary Record Route Object
          (SRRO) objects [RFC8306] are in use).

       The flags defined in this section (N, F, and E) are used in PCRpt,
       PCUpd, or PCInitiate messages.  In the case of PCReq and PCRep
       messages, these flags have no meaning and thus MUST be ignored.  The
       corresponding flags in the RP (Request Parameters) object are used as
       described in [RFC8306].

    7.1.1.  P2MP-LSP-IDENTIFIERS TLV

       [RFC8231] specifies the LSP-IDENTIFIERS TLVs to be included in the
       LSP object.  For P2MP TE LSP, this document defines P2MP-LSP-
       IDENTIFIERS TLVs for the LSP object.  There are two P2MP-LSP-
       IDENTIFIERS TLVs, one for IPv4 and one for IPv6.  The P2MP-LSP-
       IDENTIFIERS TLV MUST be included in the LSP object in a PCRpt message
       for P2MP TE LSPs.  If the N bit is set in the LSP object in the PCRpt
       message but the P2MP-LSP-IDENTIFIER TLV is absent, the PCE MUST
       respond with a PCErr message carrying error-type 6 ("mandatory object
       missing") and error-value 14 ("P2MP-LSP-IDENTIFIERS TLV missing") and
       close the PCEP session.

    Palle, et al.                Standards Track                   [Page 19]

    RFC 8623                      Stateful P2MP                    June 2019

       The P2MP-LSP-IDENTIFIERS TLV MAY be included in the LSP object in the
       PCUpd message for P2MP TE LSPs.  The special value of all zeros for
       all the fields in the value portion of the TLV is used to refer to
       all paths pertaining to a particular PLSP-ID.  The length of the TLV
       remains fixed based on the IP version.

       The P2MP-LSP-IDENTIFIERS TLV SHOULD NOT be used in a PCInitiate
       message (see Section 5.6.3.1) and MAY optionally be included in the
       LSP object in the PCReq and the PCRep message for P2MP TE LSP.

       The format of the IPV4-P2MP-LSP-IDENTIFIERS TLV is shown in Figure 1:

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |           Type=32             |           Length=16           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                   IPv4 Tunnel Sender Address                  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |             LSP ID            |           Tunnel ID           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                        Extended Tunnel ID                     |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                             P2MP ID                           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                  Figure 1: IPV4-P2MP-LSP-IDENTIFIERS TLV Format

       The type (16 bits) of the TLV is 32.  The length (16 bits) has a
       fixed value of 16 octets.  The value contains the following fields:

       IPv4 Tunnel Sender Address:  Contains the sender node's IPv4 address,
          as defined in [RFC3209].  See Section 4.6.2.1 of [RFC3209] for the
          LSP_TUNNEL_IPv4 Sender Template Object.

       LSP ID:  Contains the 16-bit 'LSP ID' identifier defined in
          [RFC3209].  See Section 4.6.2.1 of [RFC3209] for the
          LSP_TUNNEL_IPv4 Sender Template Object.

       Tunnel ID:  Contains the 16-bit 'Tunnel ID' identifier defined in
          [RFC3209].  See Section 4.6.1.1 of [RFC3209] for the
          LSP_TUNNEL_IPv4 Session Object.

       Extended Tunnel ID:  Contains the 32-bit 'Extended Tunnel ID'
          identifier defined in [RFC3209].  See Section 4.6.1.1 of [RFC3209]
          for the LSP_TUNNEL_IPv4 Session Object.

    Palle, et al.                Standards Track                   [Page 20]

    RFC 8623                      Stateful P2MP                    June 2019

       P2MP ID:  Contains the 32-bit 'P2MP ID' identifier defined in
          Section 19.1.1 of [RFC4875] for the P2MP LSP Tunnel IPv4 SESSION
          Object.

       The format of the IPV6-P2MP-LSP-IDENTIFIERS TLV is shown in Figure 2:

        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=33             |           Length=40           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       +                                                               +
       |                  IPv6 tunnel sender address                   |
       +                          (16 octets)                          +
       |                                                               |
       +                                                               +
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |             LSP ID            |           Tunnel ID           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       +                                                               +
       |                       Extended Tunnel ID                      |
       +                          (16 octets)                          +
       |                                                               |
       +                                                               +
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                             P2MP ID                           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                  Figure 2: IPV6-P2MP-LSP-IDENTIFIERS TLV Format

       The type (16 bits) of the TLV is 33.  The length (16 bits) has a
       fixed length of 40 octets.  The value contains the following fields:

       IPv6 Tunnel Sender Address:  Contains the sender node's IPv6 address,
          as defined in [RFC3209].  See Section 4.6.2.2 of [RFC3209] for the
          LSP_TUNNEL_IPv6 Sender Template Object.

       LSP ID:  Contains the 16-bit 'LSP ID' identifier defined in
          [RFC3209].  See Section 4.6.2.2 of [RFC3209] for the
          LSP_TUNNEL_IPv6 Sender Template Object.

       Tunnel ID:  Contains the 16-bit 'Tunnel ID' identifier defined in
          [RFC3209].  See Section 4.6.1.2 of [RFC3209] for the
          LSP_TUNNEL_IPv6 Session Object.

    Palle, et al.                Standards Track                   [Page 21]

    RFC 8623                      Stateful P2MP                    June 2019

       Extended Tunnel ID:  Contains the 128-bit 'Extended Tunnel ID'
          identifier defined in [RFC3209].  See Section 4.6.1.2 of [RFC3209]
          for the LSP_TUNNEL_IPv6 Session Object.

       P2MP ID:  Defined above under Figure 1.

       Tunnel ID:  Remains constant over the lifetime of a tunnel.

    7.2.  S2LS Object

       The S2LS (Source-to-Leaves) Object is used to report the state of one
       or more destinations (leaves) encoded within the END-POINTS object
       for a P2MP TE LSP.  It MUST be carried in a PCRpt message along with
       an END-POINTS object when the N flag is set in an LSP object.

       S2LS Object-Class is 41.

       S2LS Object-Types is 1.

       The format of the S2LS object 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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                             Flags                       |    O|
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       //                      Optional TLVs                          //
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                           Figure 3: S2LS Object Format

       Flags (32 bits):  The following flag is currently defined:

       O (Operational - 3 bits)  The O field represents the operational
          status of the group of destinations.  The values are as per the
          Operational field in the LSP object defined in Section 7.3 of
          [RFC8231].

       Unassigned bits are reserved for future uses.  They MUST be set to 0
       on transmission and MUST be ignored on receipt.

       When the N flag is set in an LSP object, the O field in the LSP
       object represents the operational status of the full P2MP TE LSP, and
       the O field in the S2LS object represents the operational status of a
       group of destinations encoded within the END-POINTS object.  If there
       is a conflict between the O field in the LSP and the S2LS object (for

    Palle, et al.                Standards Track                   [Page 22]

    RFC 8623                      Stateful P2MP                    June 2019

       example, the O field in the LSP corresponds to down whereas the O
       field in the S2LS is up), the PCEP speaker MUST generate an error
       with error-type 10 ("Reception of an invalid object") and error-value
       22 ("Mismatch of O field in S2LS and LSP object").

       Future documents might define optional TLVs that could be included in
       the S2LS Object.

    8.  Message Fragmentation

       The total PCEP message length, including the common header, is
       (2^16)-1 bytes.  In certain scenarios, the P2MP report and update
       request may not fit into a single PCEP message (e.g., initial report
       or update).  The F flag is used in the LSP object to signal that the
       initial report, update, or initiate request was too large to fit into
       a single PCEP message and will be fragmented into multiple messages.
       In order to identify the single report or update, each message will
       use the same PLSP-ID.  In order to identify that a series of
       PCInitiate messages represents a single Initiate, each message will
       use the same PLSP-ID (in this case 0) and SRP-ID-number.

       The fragmentation procedure described below for report or update
       messages is similar to [RFC8306], which describes request and
       response message fragmentation.

    8.1.  Report Fragmentation Procedure

       If the initial report is too large to fit into a single report
       message, the PCC will split the report over multiple messages.  Each
       message sent to the PCE, except the last one, will have the F flag
       set in the LSP object to signify that the report has been fragmented
       into multiple messages.  In order to identify that a series of report
       messages represents a single report, each message will use the same
       PLSP-ID.

       The Error-Type value 18 ("P2MP Fragmentation Error") is used to
       report any error associated with the fragmentation of a P2MP PCEP
       message.  A new error-value 2 indicates "Fragmented report failure"
       and is used if a PCE does not receive the last part of the fragmented
       message.

    8.2.  Update Fragmentation Procedure

       Once the PCE computes and updates a path for some or all leaves in a
       P2MP TE LSP, an update message is sent to the PCC.  If the update is
       too large to fit into a single update message, the PCE will split the
       update over multiple messages.  Each update message sent by the PCE,
       except the last one, will have the F flag set in the LSP object to

    Palle, et al.                Standards Track                   [Page 23]

    RFC 8623                      Stateful P2MP                    June 2019

       signify that the update has been fragmented into multiple messages.
       In order to identify that a series of update messages represents a
       single update, each message will use the same PLSP-ID and SRP-ID-
       number.

       The Error-Type value 18 ("P2MP Fragmentation Error") is used to
       report any error associated with the fragmentation of a P2MP PCEP
       message.  A new error-value 3 indicates "Fragmented update failure"
       and is used if a PCC does not receive the last part of the fragmented
       message.

    8.3.  PCInitiate Fragmentation Procedure

       Once the PCE initiates to set up a P2MP TE LSP, a PCInitiate message
       is sent to the PCC.  If the initiate request is too large to fit into
       a single PCInitiate message, the PCE will split the initiate request
       over multiple messages.  Each PCInitiate message sent by the PCE,
       except the last one, will have the F flag set in the LSP object to
       signify that the PCInitiate has been fragmented into multiple
       messages.  In order to identify that a series of PCInitiate messages
       represents a single Initiate, each message will use the same PLSP-ID
       (in this case 0) and SRP-ID-number.

       The Error-Type value 18 ("P2MP Fragmentation Error") is used to
       report any error associated with the fragmentation of a P2MP PCEP
       message.  A new error-value 4 indicates "Fragmented instantiation
       failure" and is used if a PCC does not receive the last part of the
       fragmented message.

    9.  Nonsupport of P2MP TE LSPs for Stateful PCE

       The PCEP extensions described in this document for stateful PCEs with
       P2MP capability MUST NOT be used if the PCE has not advertised its
       stateful capability with P2MP as per Section 5.2.  If the PCC
       supports the extensions as per this document (understands the N
       (P2MP-CAPABILITY) and M (P2MP-LSP-UPDATE-CAPABILITY) flags in the LSP
       object) but did not advertise this capability, then upon receipt of a
       PCUpd message from the PCE, it SHOULD generate a PCErr with error-
       type 19 ("Invalid Operation"), error-value 12 ("Attempted LSP Update
       Request for P2MP if active stateful PCE capability for P2MP was not
       advertised"), and terminate the PCEP session.  If the PCE supports
       the extensions as per this document (understands the N (P2MP-
       CAPABILITY) flag in the LSP object) but did not advertise this
       capability, then upon receipt of a PCRpt message from the PCC, it
       SHOULD generate a PCErr with error-type 19 ("Invalid Operation"),
       error-value 11 ("Attempted LSP State Report for P2MP if stateful PCE
       capability for P2MP was not advertised"), and it SHOULD terminate the
       PCEP session.

    Palle, et al.                Standards Track                   [Page 24]

    RFC 8623                      Stateful P2MP                    June 2019

       If a Stateful PCE receives a P2MP TE LSP report message and the PCE
       does not understand the N (P2MP-CAPABILITY) flag in the LSP object,
       and therefore the PCEP extensions described in this document, then
       the Stateful PCE would act as per Section 6.1 of [RFC8231] (and
       consider the PCRpt message as invalid).

       The PCEP extensions described in this document for PCC or PCE with
       the PCE-Initiation capability for P2MP TE LSPs MUST NOT be used if
       the PCC or PCE has not advertised its stateful capability with
       Instantiation and P2MP capability as per Section 5.2.  If the PCC
       supports the extensions as per this document (understands the P
       (P2MP-LSP-INSTANTIATION-CAPABILITY) flag) but did not advertise this
       capability, then upon receipt of a PCInitiate message from the PCE,
       it SHOULD generate a PCErr with error-type 19 ("Invalid Operation"),
       error-value 13 ("Attempted LSP Instantiation Request for P2MP if
       stateful PCE instantiation capability for P2MP was not advertised"),
       and terminate the PCEP session.

    10.  Manageability Considerations

       All manageability requirements and considerations listed in
       [RFC5440], [RFC8306], [RFC8231], and [RFC8281] apply to PCEP
       extensions defined in this document.  In addition, requirements and
       considerations listed in this section apply.

    10.1.  Control of Function and Policy

       A PCE or PCC implementation MUST allow configuration of the stateful
       PCEP capability, the LSP Update capability, and the LSP Initiation
       capability for P2MP LSPs.

    10.2.  Information and Data Models

       The PCEP YANG module [PCE-PCEP-YANG] can be extended to include
       advertised P2MP stateful capabilities, P2MP synchronization status,
       and the delegation status of a P2MP LSP, etc.  The statistics module
       should also count data related to P2MP LSPs.

    10.3.  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].

    Palle, et al.                Standards Track                   [Page 25]

    RFC 8623                      Stateful P2MP                    June 2019

    10.4.  Verify Correct Operations

       Mechanisms defined in this document do not imply any new operation
       verification requirements in addition to those already listed in
       [RFC5440], [RFC8306], [RFC8231], and [RFC8281].

    10.5.  Requirements on Other Protocols

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

    10.6.  Impact on Network Operations

       Mechanisms defined in this document do not have any impact on network
       operations in addition to those already listed in [RFC5440],
       [RFC8306], [RFC8231], and [RFC8281].

       Stateful PCE features for P2MP LSPs would help with network
       operations.

    11.  IANA Considerations

       IANA has registered the code points for the protocol elements defined
       in this document.

    11.1.  PCE Capabilities in IGP Advertisements

       IANA has registered the new bits in the OSPF Parameters "Path
       Computation Element (PCE) Capability Flags" registry, as follows:

              Bit      Capability Description              Reference

              13       Active Stateful PCE with P2MP       RFC 8623
              14       Passive Stateful PCE with P2MP      RFC 8623
              15       Stateful PCE Initiation with P2MP   RFC 8623

    11.2.  STATEFUL-PCE-CAPABILITY TLV

       The STATEFUL-PCE-CAPABILITY TLV is defined in [RFC8231], and the
       "STATEFUL-PCE-CAPABILITY TLV Flag Field" subregistry was created to
       manage the flags in the TLV.  IANA has registered the following code
       points in the aforementioned registry.

           Bit    Description                            Reference

           23      P2MP-LSP-INSTANTIATION-CAPABILITY     RFC 8623
           24      P2MP-LSP-UPDATE-CAPABILITY            RFC 8623
           25      P2MP-CAPABILITY                       RFC 8623

    Palle, et al.                Standards Track                   [Page 26]

    RFC 8623                      Stateful P2MP                    June 2019

    11.3.  LSP Object

       The LSP object is defined in [RFC8231], and the "LSP Object Flag
       Field" subregistry was created to manage the Flags field of the LSP
       object.

       IANA has registered the following code points in the aforementioned
       registry.

           Bit    Description           Reference

           1      ERO-compression       RFC 8623
           2      Fragmentation         RFC 8623
           3      P2MP                  RFC 8623

    11.4.  PCEP-ERROR Object

       IANA has registered the new error values within the "PCEP-ERROR
       Object Error Types and Values" subregistry of the PCEP Numbers
       registry, as follows:

           Error-Type  Meaning
              6        Mandatory Object missing [RFC5440]
                         Error-value = 13: S2LS object missing
                         Error-value = 14: P2MP-LSP-IDENTIFIERS TLV missing
              10       Reception of an invalid object [RFC5440]
                         Error-value = 22: Mismatch of O field in S2LS
                             and LSP object
              18       P2MP Fragmentation Error [RFC8306]
                         Error-value = 2: Fragmented Report failure
                         Error-value = 3: Fragmented Update failure
                         Error-value = 4: Fragmented Instantiation failure
              19       Invalid Operation [RFC8231]
                         Error-value = 11: Attempted LSP State Report
                             for P2MP if stateful PCE capability
                             for P2MP was not advertised
                         Error-value = 12: Attempted LSP Update Request
                             for P2MP if active stateful PCE capability
                             for P2MP was not advertised
                         Error-value = 13: Attempted LSP Instantiation
                             Request for P2MP if stateful PCE
                             instantiation capability for P2MP was not
                             advertised

       The reference for all new Error-values above is RFC 8623.

    Palle, et al.                Standards Track                   [Page 27]

    RFC 8623                      Stateful P2MP                    June 2019

    11.5.  PCEP TLV Type Indicators

       IANA has registered the following code points in the existing "PCEP
       TLV Type Indicators" registry as follows:

              Value     Description                       Reference

                32      P2MP-IPV4-LSP-IDENTIFIERS         RFC 8623
                33      P2MP-IPV6-LSP-IDENTIFIERS         RFC 8623

    11.6.  PCEP Object

       IANA has registered the new object-class values and object types
       within the "PCEP Objects" subregistry of the PCEP Numbers registry,
       as follows.

           Object-Class Value  Name                               Reference

                   41          S2LS                               RFC 8623
                               Object-Type
                               0: Reserved
                               1: S2LS

    11.7.  S2LS Object

       A new subregistry, named "S2LS Object Flag Field", has been created
       within the "Path Computation Element Protocol (PCEP) Numbers"
       registry to manage the 32-bit flag field of the S2LS object.  New
       values are to be assigned by Standards Action [RFC8126].  Each bit
       should be tracked with the following qualities:

       o  Bit number (counting from bit 0 as the most significant bit)

       o  Capability description

       o  Defining RFC

       The following values are defined in this document:

                        Bit     Description           Reference

                        0-28    Unassigned
                       29-31    Operational (3 bits)  RFC 8623

    Palle, et al.                Standards Track                   [Page 28]

    RFC 8623                      Stateful P2MP                    June 2019

    12.  Security Considerations

       The stateful operations on P2MP TE LSPs are more CPU intensive and
       also utilize more bandwidth on the wire (in comparison to P2P TE
       LSPs).  If a rogue PCC were able to request unauthorized stateful PCE
       operations, then it may be able to mount a DoS attack against a PCE,
       which would disrupt the network and deny service to other PCCs.
       Similarly, an attacker may flood the PCC with PCUpd messages at a
       rate that exceeds either the PCC's ability to process them or the
       network's ability to signal the changes by either spoofing messages
       or compromising the PCE itself.

       Consequently, it is important that implementations conform to the
       relevant security requirements as listed below:

       o  As per [RFC8231], it is RECOMMENDED that these PCEP extensions
          only be activated on authenticated and encrypted sessions across
          PCEs and PCCs belonging to the same administrative authority,
          using Transport Layer Security (TLS) [RFC8253] as per the
          recommendations and best current practices in [RFC7525] (unless
          explicitly set aside in [RFC8253]).

       o  Security considerations for path computation requests and
          responses are as per [RFC8306].

       o  Security considerations for stateful operations (such as state
          report, synchronization, delegation, update, etc.) are as per
          [RFC8231].

       o  Security considerations for the LSP instantiation mechanism are as
          per [RFC8231].

       o  Security considerations as stated in Sections 10.1, 10.6, and 10.7
          of [RFC5440] continue to apply.

    13.  References

    13.1.  Normative References

       [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>.

       [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/info/rfc3209>.

    Palle, et al.                Standards Track                   [Page 29]

    RFC 8623                      Stateful P2MP                    June 2019

       [RFC4875]  Aggarwal, R., Ed., Papadimitriou, D., Ed., and
                  S. Yasukawa, Ed., "Extensions to Resource Reservation
                  Protocol - Traffic Engineering (RSVP-TE) for Point-to-
                  Multipoint TE Label Switched Paths (LSPs)", RFC 4875,
                  DOI 10.17487/RFC4875, May 2007,
                  <https://www.rfc-editor.org/info/rfc4875>.

       [RFC5088]  Le Roux, JL., Ed., Vasseur, JP., Ed., Ikejiri, Y., and
                  R. Zhang, "OSPF Protocol Extensions for Path Computation
                  Element (PCE) Discovery", RFC 5088, DOI 10.17487/RFC5088,
                  January 2008, <https://www.rfc-editor.org/info/rfc5088>.

       [RFC5089]  Le Roux, JL., Ed., Vasseur, JP., Ed., Ikejiri, Y., and
                  R. Zhang, "IS-IS Protocol Extensions for Path Computation
                  Element (PCE) Discovery", RFC 5089, DOI 10.17487/RFC5089,
                  January 2008, <https://www.rfc-editor.org/info/rfc5089>.

       [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>.

       [RFC5511]  Farrel, A., "Routing Backus-Naur Form (RBNF): A Syntax
                  Used to Form Encoding Rules in Various Routing Protocol
                  Specifications", RFC 5511, DOI 10.17487/RFC5511, April
                  2009, <https://www.rfc-editor.org/info/rfc5511>.

       [RFC7525]  Sheffer, Y., Holz, R., and P. Saint-Andre,
                  "Recommendations for Secure Use of Transport Layer
                  Security (TLS) and Datagram Transport Layer Security
                  (DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
                  2015, <https://www.rfc-editor.org/info/rfc7525>.

       [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>.

       [RFC8232]  Crabbe, E., Minei, I., Medved, J., Varga, R., Zhang, X.,
                  and D. Dhody, "Optimizations of Label Switched Path State
                  Synchronization Procedures for a Stateful PCE", RFC 8232,
                  DOI 10.17487/RFC8232, September 2017,
                  <https://www.rfc-editor.org/info/rfc8232>.

    Palle, et al.                Standards Track                   [Page 30]

    RFC 8623                      Stateful P2MP                    June 2019

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

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

       [RFC8306]  Zhao, Q., Dhody, D., Ed., Palleti, R., and D. King,
                  "Extensions to the Path Computation Element Communication
                  Protocol (PCEP) for Point-to-Multipoint Traffic
                  Engineering Label Switched Paths", RFC 8306,
                  DOI 10.17487/RFC8306, November 2017,
                  <https://www.rfc-editor.org/info/rfc8306>.

    13.2.  Informative References

       [PCE-PCEP-YANG]
                  Dhody, D., Hardwick, J., Beeram, V., and J. Tantsura, "A
                  YANG Data Model for Path Computation Element
                  Communications Protocol (PCEP)", Work in Progress,
                  draft-ietf-pce-pcep-yang-11, March 2019.

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

       [RFC5671]  Yasukawa, S. and A. Farrel, Ed., "Applicability of the
                  Path Computation Element (PCE) to Point-to-Multipoint
                  (P2MP) MPLS and GMPLS Traffic Engineering (TE)", RFC 5671,
                  DOI 10.17487/RFC5671, October 2009,
                  <https://www.rfc-editor.org/info/rfc5671>.

       [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/info/rfc8051>.

       [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>.

    Palle, et al.                Standards Track                   [Page 31]

    RFC 8623                      Stateful P2MP                    June 2019

    Acknowledgments

       Thanks to Quintin Zhao, Avantika, and Venugopal Reddy for the review
       comments.

       Thanks to Adrian Farrel (and Jonathan Hardwick) for the review as
       document shepherds.

       Thanks to Andy Malis for the RTG-DIR review.  Thanks to Donald
       Eastlake for the SEC-DIR review.  Thanks to David Schinazi for the
       GEN-ART review.

       Thanks to Suresh Krishnan, Mirja Kuhlewind, Roman Danyliw, and
       Benjamin Kaduk for the IESG reviews.

    Contributors

       Yuji Kamite
       NTT Communications Corporation
       Granpark Tower
       3-4-1 Shibaura, Minato-ku
       Tokyo  108-8118
       Japan

       Email: y.kamite@ntt.com

    Palle, et al.                Standards Track                   [Page 32]

    RFC 8623                      Stateful P2MP                    June 2019

    Authors' Addresses

       Udayasree Palle
       Huawei Technologies

       Email: udayasreereddy@gmail.com

       Dhruv Dhody
       Huawei Technologies
       Divyashree Techno Park, Whitefield
       Bangalore, Karnataka  560066
       India

       Email: dhruv.ietf@gmail.com

       Yosuke Tanaka
       NTT Communications Corporation
       Granpark Tower
       3-4-1 Shibaura, Minato-ku
       Tokyo  108-8118
       Japan

       Email: yosuke.tanaka@ntt.com

       Vishnu Pavan Beeram
       Juniper Networks

       Email: vbeeram@juniper.net

    Palle, et al.                Standards Track                   [Page 33]