path: root/doc/rfc/rfc8306.txt

Internet Engineering Task Force (IETF)                           Q. Zhao
Request for Comments: 8306                                 D. Dhody, Ed.
Obsoletes: 6006                                               R. Palleti
Category: Standards Track                            Huawei Technologies
ISSN: 2070-1721                                                  D. King
                                                      Old Dog Consulting
                                                           November 2017


                             Extensions to
       the Path Computation Element Communication Protocol (PCEP)
    for Point-to-Multipoint Traffic Engineering Label Switched Paths

Abstract

   Point-to-point Multiprotocol Label Switching (MPLS) and Generalized
   MPLS (GMPLS) Traffic Engineering Label Switched Paths (TE LSPs) may
   be established using signaling techniques, but their paths may first
   need to be determined.  The Path Computation Element (PCE) has been
   identified as an appropriate technology for the determination of the
   paths of point-to-multipoint (P2MP) TE LSPs.

   This document describes extensions to the PCE Communication Protocol
   (PCEP) to handle requests and responses for the computation of paths
   for P2MP TE LSPs.

   This document obsoletes RFC 6006.

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/rfc8306.










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Copyright Notice

   Copyright (c) 2017 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
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   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.

   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November
   10, 2008.  The person(s) controlling the copyright in some of this
   material may not have granted the IETF Trust the right to allow
   modifications of such material outside the IETF Standards Process.
   Without obtaining an adequate license from the person(s) controlling
   the copyright in such materials, this document may not be modified
   outside the IETF Standards Process, and derivative works of it may
   not be created outside the IETF Standards Process, except to format
   it for publication as an RFC or to translate it into languages other
   than English.

Table of Contents

   1. Introduction ....................................................4
      1.1. Terminology ................................................5
      1.2. Requirements Language ......................................5
   2. PCC-PCE Communication Requirements ..............................5
   3. Protocol Procedures and Extensions ..............................6
      3.1. P2MP Capability Advertisement ..............................7
           3.1.1. IGP Extensions for P2MP Capability Advertisement ....7
           3.1.2. Open Message Extension ..............................7
      3.2. Efficient Presentation of P2MP LSPs ........................8
      3.3. P2MP Path Computation Request/Reply Message Extensions .....9
           3.3.1. The Extension of the RP Object ......................9
           3.3.2. The P2MP END-POINTS Object .........................11
      3.4. Request Message Format ....................................13
      3.5. Reply Message Format ......................................15








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      3.6. P2MP Objective Functions and Metric Types .................16
           3.6.1. Objective Functions ................................16
           3.6.2. METRIC Object-Type Values ..........................17
      3.7. Non-Support of P2MP Path Computation ......................17
      3.8. Non-Support by Back-Level PCE Implementations .............17
      3.9. P2MP TE Path Reoptimization Request .......................17
      3.10. Adding and Pruning Leaves to/from the P2MP Tree ..........18
      3.11. Discovering Branch Nodes .................................22
           3.11.1. Branch Node Object ................................22
      3.12. Synchronization of P2MP TE Path Computation Requests .....22
      3.13. Request and Response Fragmentation .......................23
           3.13.1. Request Fragmentation Procedure ...................24
           3.13.2. Response Fragmentation Procedure ..................24
           3.13.3. Fragmentation Example .............................24
      3.14. UNREACH-DESTINATION Object ...............................25
      3.15. P2MP PCEP-ERROR Objects and Types ........................27
      3.16. PCEP NO-PATH Indicator ...................................28
   4. Manageability Considerations ...................................28
      4.1. Control of Function and Policy ............................28
      4.2. Information and Data Models ...............................28
      4.3. Liveness Detection and Monitoring .........................29
      4.4. Verifying Correct Operation ...............................29
      4.5. Requirements for Other Protocols and Functional
           Components ................................................29
      4.6. Impact on Network Operation ...............................29
   5. Security Considerations ........................................30
   6. IANA Considerations ............................................31
      6.1. PCEP TLV Type Indicators ..................................31
      6.2. Request Parameter Bit Flags ...............................31
      6.3. Objective Functions .......................................31
      6.4. METRIC Object-Type Values .................................32
      6.5. PCEP Objects ..............................................32
      6.6. PCEP-ERROR Objects and Types ..............................34
      6.7. PCEP NO-PATH Indicator ....................................35
      6.8. SVEC Object Flag ..........................................35
      6.9. OSPF PCE Capability Flag ..................................35
   7. References .....................................................36
      7.1. Normative References ......................................36
      7.2. Informative References ....................................37
   Appendix A. Summary of Changes from RFC 6006 ......................39
   Appendix A.1. RBNF Changes from RFC 6006 ..........................39
   Acknowledgements ..................................................41
   Contributors ......................................................42
   Authors' Addresses ................................................43







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1.  Introduction

   The Path Computation Element (PCE) as defined in [RFC4655] 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.

   The PCE has been identified as a suitable application for the
   computation of paths for P2MP TE LSPs [RFC5671].

   The PCE Communication Protocol (PCEP) is designed as a communication
   protocol between PCCs and PCEs for point-to-point (P2P) path
   computations and is defined in [RFC5440].  However, that
   specification does not provide a mechanism to request path
   computation of P2MP TE LSPs.

   A P2MP LSP is comprised of multiple source-to-leaf (S2L) sub-LSPs.
   These S2L sub-LSPs are set up between ingress and egress Label
   Switching Routers (LSRs) and are appropriately overlaid to construct
   a P2MP TE LSP.  During path computation, the P2MP TE LSP may be
   determined as a set of S2L sub-LSPs that are computed separately and
   combined to give the path of the P2MP LSP, or the entire P2MP TE LSP
   may be determined as a P2MP tree in a single computation.

   This document relies on the mechanisms of PCEP to request path
   computation for P2MP TE LSPs.  One Path Computation Request message
   from a PCC may request the computation of the whole P2MP TE LSP, or
   the request may be limited to a subset of the S2L sub-LSPs.  In the
   extreme case, the PCC may request the S2L sub-LSPs to be computed
   individually; the PCC is responsible for deciding whether to signal
   individual S2L sub-LSPs or combine the computation results to signal
   the entire P2MP TE LSP.  Hence, the PCC may use one Path Computation
   Request message or may split the request across multiple path
   computation messages.

   This document obsoletes [RFC6006] and incorporates the following
   errata:

   o  Erratum IDs 3819, 3830, 3836, 4867, and 4868 for [RFC6006]

   o  Erratum ID 4956 for [RFC5440]

   All changes from [RFC6006] are listed in Appendix A.



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1.1.  Terminology

   Terminology used in this document:

   TE LSP: Traffic Engineering Label Switched Path.

   LSR: Label Switching Router.

   OF: Objective Function.  A set of one or more optimization criteria
      used for the computation of a single path (e.g., path cost
      minimization) or for the synchronized computation of a set of
      paths (e.g., aggregate bandwidth consumption minimization).

   P2MP: Point-to-Multipoint.

   P2P: Point-to-Point.

   This document also uses the terminology defined in [RFC4655],
   [RFC4875], and [RFC5440].

1.2.  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.  PCC-PCE Communication Requirements

   This section summarizes the PCC-PCE communication requirements as met
   by the protocol extension specified in this document for P2MP MPLS-TE
   LSPs.  The numbering system in the list below corresponds to the
   requirement numbers (e.g., R1, R2) used in [RFC5862].

   1.  The PCC MUST be able to specify that the request is a P2MP path
       computation request.

   2.  The PCC MUST be able to specify that objective functions are to
       be applied to the P2MP path computation request.

   3.  The PCE MUST have the capability to reject a P2MP path
       computation request and indicate non-support of P2MP path
       computation.

   4.  The PCE MUST provide an indication of non-support of P2MP path
       computation by back-level PCE implementations.




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   5.  A P2MP path computation request MUST be able to list multiple
       destinations.

   6.  A P2MP path computation response MUST be able to carry the path
       of a P2MP LSP.

   7.  By default, the path returned by the PCE SHOULD use the
       compressed format.

   8.  It MUST be possible for a single P2MP path computation request or
       response to be conveyed by a sequence of messages.

   9.  It MUST NOT be possible for a single P2MP path computation
       request to specify a set of different constraints, traffic
       parameters, or quality-of-service requirements for different
       destinations of a P2MP LSP.

   10. P2MP path modification and P2MP path diversity MUST be supported.

   11. It MUST be possible to reoptimize existing P2MP TE LSPs.

   12. It MUST be possible to add and remove P2MP destinations from
       existing paths.

   13. It MUST be possible to specify a list of applicable branch nodes
       to use when computing the P2MP path.

   14. It MUST be possible for a PCC to discover P2MP path computation
       capability.

   15. The PCC MUST be able to request diverse paths when requesting a
       P2MP path.

3.  Protocol Procedures and Extensions

   The following section describes the protocol extensions required to
   satisfy the requirements specified in Section 2 ("PCC-PCE
   Communication Requirements") of this document.













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3.1.  P2MP Capability Advertisement

3.1.1.  IGP Extensions for P2MP Capability Advertisement

   [RFC5088] defines a PCE Discovery (PCED) TLV carried in an OSPF
   Router Information Link State Advertisement (LSA) as defined in
   [RFC7770] to facilitate PCE discovery using OSPF.  [RFC5088]
   specifies that no new sub-TLVs may be added to the PCED TLV.  This
   document defines a flag in the OSPF PCE Capability Flags to indicate
   the capability of P2MP computation.

   Similarly, [RFC5089] defines the PCED sub-TLV for use in PCE
   discovery using IS-IS.  This document will use the same flag for the
   OSPF PCE Capability Flags sub-TLV to allow IS-IS to indicate the
   capability of P2MP computation.

   The IANA assignment for a shared OSPF and IS-IS P2MP Capability Flag
   is documented in Section 6.9 ("OSPF PCE Capability Flag") of this
   document.

   PCEs wishing to advertise that they support P2MP path computation
   would set the bit (10) accordingly.  PCCs that do not understand this
   bit will ignore it (per [RFC5088] and [RFC5089]).  PCEs that do not
   support P2MP will leave the bit clear (per the default behavior
   defined in [RFC5088] and [RFC5089]).

   PCEs that set the bit to indicate support of P2MP path computation
   MUST follow the procedures in Section 3.3.2 ("The P2MP END-POINTS
   Object") to further qualify the level of support.

3.1.2.  Open Message Extension

   Based on the Capabilities Exchange requirement described in
   [RFC5862], if a PCE does not advertise its P2MP capability during
   discovery, PCEP should be used to allow a PCC to discover, during the
   Open Message Exchange, which PCEs are capable of supporting P2MP path
   computation.

   To satisfy this requirement, we extend the PCEP OPEN object by
   defining an optional TLV to indicate the PCE's capability to perform
   P2MP path computations.

   IANA has allocated value 6 from the "PCEP TLV Type Indicators"
   subregistry, as documented in Section 6.1 ("PCEP TLV Type
   Indicators").  The description is "P2MP capable", and the length
   value is 2 bytes.  The value field is set to default value 0.





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   The inclusion of this TLV in an OPEN object indicates that the sender
   can perform P2MP path computations.

   The capability TLV is meaningful only for a PCE, so it will typically
   appear only in one of the two Open messages during PCE session
   establishment.  However, in the case of PCE cooperation (e.g.,
   inter-domain), when a PCE behaving as a PCC initiates a PCE session
   it SHOULD also indicate its path computation capabilities.

3.2.  Efficient Presentation of P2MP LSPs

   When specifying additional leaves or when optimizing existing P2MP TE
   LSPs as specified in [RFC5862], it may be necessary to pass existing
   P2MP LSP route information between the PCC and PCE in the request and
   reply messages.  In each of these scenarios, we need path objects for
   efficiently passing the existing P2MP LSP between the PCE and PCC.

   We specify the use of the Resource Reservation Protocol Traffic
   Engineering (RSVP-TE) extensions Explicit Route Object (ERO) to
   encode the explicit route of a TE LSP through the network.  PCEP ERO
   sub-object types correspond to RSVP-TE ERO sub-object types.  The
   format and content of the ERO are defined in [RFC3209] and [RFC3473].

   The Secondary Explicit Route Object (SERO) is used to specify the
   explicit route of an S2L sub-LSP.  The path of each subsequent S2L
   sub-LSP is encoded in a P2MP_SECONDARY_EXPLICIT_ROUTE object SERO.
   The format of the SERO is the same as the format of an ERO as defined
   in [RFC3209] and [RFC3473].

   The Secondary Record Route Object (SRRO) is used to record the
   explicit route of the S2L sub-LSP.  The class of the P2MP SRRO is the
   same as the class of the SRRO as defined in [RFC4873].

   The SERO and SRRO are used to report the route of an existing TE LSP
   for which a reoptimization is desired.  The format and content of the
   SERO and SRRO are defined in [RFC4875].















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   PCEP Object-Class and Object-Type values for the SERO and SRRO have
   been assigned:

      Object-Class Value    29
      Name                  SERO
      Object-Type           0: Reserved
                            1: SERO
                            2-15: Unassigned
      Reference             RFC 8306

      Object-Class Value    30
      Name                  SRRO
      Object-Type           0: Reserved
                            1: SRRO
                            2-15: Unassigned
      Reference             RFC 8306

   The IANA assignments are documented in Section 6.5 ("PCEP Objects").

   Since the explicit path is available for immediate signaling by the
   MPLS or GMPLS control plane, the meanings of all of the sub-objects
   and fields in this object are identical to those defined for the ERO.

3.3.  P2MP Path Computation Request/Reply Message Extensions

   This document extends the existing P2P RP (Request Parameters) object
   so that a PCC can signal a P2MP path computation request to the PCE
   receiving the PCEP request.  The END-POINTS object is also extended
   to improve the efficiency of the message exchange between the PCC and
   PCE in the case of P2MP path computation.

3.3.1.  The Extension of the RP Object

   The PCE path computation request and reply messages will need the
   following additional parameters to indicate to the receiving PCE
   (1) that the request and reply messages have been fragmented across
   multiple messages, (2) that they have been requested for a P2MP path,
   and (3) whether the route is represented in the compressed or
   uncompressed format.












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   This document adds the following flags to the RP object:

   The F-bit is added to the flag bits of the RP object to indicate to
   the receiver that the request is part of a fragmented request or
   is not a fragmented request.

   o  F (RP fragmentation bit - 1 bit):

      0: This indicates that the RP is not fragmented or it is the last
         piece of the fragmented RP.

      1: This indicates that the RP is fragmented and this is not the
         last piece of the fragmented RP.  The receiver needs to wait
         for additional fragments until it receives an RP with the same
         RP-ID and with the F-bit set to 0.

   The N-bit is added in the flag bits field of the RP object to signal
   the receiver of the message that the request/reply is for P2MP or
   is not for P2MP.

   o  N (P2MP bit - 1 bit):

      0: This indicates that this is not a Path Computation Request
         (PCReq) or Path Computation Reply (PCRep) message for P2MP.

      1: This indicates that this is a PCReq or PCRep message for P2MP.

   The E-bit is added in the flag bits field of the RP object to signal
   the receiver of the message that the route is in the compressed
   format or is not in the compressed format.  By default, the path
   returned by the PCE SHOULD use the compressed format.

   o  E (ERO-compression bit - 1 bit):

      0: This indicates that the route is not in the compressed format.

      1: This indicates that the route is in the compressed format.

   The IANA assignments are documented in Section 6.2 ("Request
   Parameter Bit Flags") of this document.











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3.3.2.  The P2MP END-POINTS Object

   The END-POINTS object is used in a PCReq message to specify the
   source IP address and the destination IP address of the path for
   which a path computation is requested.  To represent the end points
   for a P2MP path efficiently, we define two types of END-POINTS
   objects for the P2MP path:

   o  Old leaves whose path can be modified/reoptimized.

   o  Old leaves whose path must be left unchanged.

   With the P2MP END-POINTS object, the PCE Path Computation Request
   message is expanded in a way that allows a single request message to
   list multiple destinations.

   In total, there are now four possible types of leaves in a
   P2MP request:

   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)

   A given END-POINTS object gathers the leaves of a given type.  The
   type of leaf in a given END-POINTS object is identified by the
   END-POINTS object leaf type field.

   Using the P2MP END-POINTS object, the END-POINTS portion of a request
   message for the multiple destinations can be reduced by up to 50% for
   a P2MP path where a single source address has a very large number of
   destinations.

   Note that a P2MP path computation request can mix the different types
   of leaves by including several END-POINTS objects per RP object as
   shown in the PCReq Routing Backus-Naur Form (RBNF) [RFC5511] format
   in Section 3.4 ("Request Message Format").











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   The format of the P2MP END-POINTS object body for IPv4
   (Object-Type 3) is as follows:

     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                          Leaf type                            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                     Source IPv4 address                       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                  Destination IPv4 address                     |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ~                           ...                                 ~
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                  Destination IPv4 address                     |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

         Figure 1: The P2MP END-POINTS Object Body Format for IPv4

   The format of the END-POINTS object body for IPv6 (Object-Type 4) is
   as follows:

     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                          Leaf type                            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    |                Source IPv6 address (16 bytes)                 |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    |              Destination IPv6 address (16 bytes)              |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ~                           ...                                 ~
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    |              Destination IPv6 address (16 bytes)              |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

         Figure 2: The P2MP END-POINTS Object Body Format for IPv6








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   The END-POINTS object body has a variable length.  These are

   o  multiples of 4 bytes for IPv4

   o  multiples of 16 bytes, plus 4 bytes, for IPv6

3.4.  Request Message Format

   As per [RFC5440], a Path Computation Request message (also referred
   to as a PCReq message) is a PCEP message sent by a PCC to a PCE to
   request a path computation.  A PCReq message may carry more than one
   path computation request.

   As per [RFC5541], the OF object MAY be carried within a PCReq
   message.  If an objective function is to be applied to a set of
   synchronized path computation requests, the OF object MUST be carried
   just after the corresponding SVEC (Synchronization Vector) object and
   MUST NOT be repeated for each elementary request.

   The PCReq message is encoded as follows using RBNF as defined in
   [RFC5511].






























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   Below is the message format for the request message:

        <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>
                          [<OF>]
                          [<LSPA>]
                          [<BANDWIDTH>]
                          [<metric-list>]
                          [<IRO>|<BNC>]
                          [<LOAD-BALANCING>]

        where:

             <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>]

           Figure 3: The Message Format for the Request Message

   Note that we preserve compatibility with the definition of <request>
   provided in [RFC5440].  At least one instance of <END-POINTS> MUST be
   present in this message.

   We have documented the IANA assignment of additional END-POINTS
   Object-Type values in Section 6.5 ("PCEP Objects") of this document.










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3.5.  Reply Message Format

   The PCEP Path Computation Reply message (also referred to as a
   PCRep message) is a PCEP message sent by a PCE to a requesting PCC in
   response to a previously received PCReq message.  PCEP supports the
   bundling of multiple replies to a set of path computation requests
   within a single PCRep message.

   The PCRep message is encoded as follows using RBNF as defined in
   [RFC5511].

   Below is the message format for the reply message:

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

        where:

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

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

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

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

        where:

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

            Figure 4: The Message Format for the Reply Message

   The optional END-POINTS object in the reply message is used to
   specify which paths are removed, changed, not changed, or added for
   the request.  The path is only needed for the end points that are
   added or changed.





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   If the E-bit (ERO-Compress bit) was set to 1 in the request, then the
   path will be formed by an ERO followed by a list of SEROs.

   Note that we preserve compatibility with the definition of <response>
   provided in [RFC5440] and with the optional
   <end-point-path-pair-list> and <path>.

3.6.  P2MP Objective Functions and Metric Types

3.6.1.  Objective Functions

   Six objective functions have been defined in [RFC5541] for P2P path
   computation.

   This document defines two additional objective functions -- namely,
   SPT (Shortest-Path Tree) and MCT (Minimum-Cost Tree) -- that apply to
   P2MP path computation.  Hence, two objective function codes are
   defined as follows:

   Objective Function Code: 7

      Name: Shortest-Path Tree (SPT)

      Description: Minimize the maximum source-to-leaf cost with respect
      to a specific metric or to the TE metric used as the default
      metric when the metric is not specified (e.g., TE or IGP metric).

   Objective Function Code: 8

      Name: Minimum-Cost Tree (MCT)

      Description: Minimize the total cost of the tree (i.e., the sum of
      the costs of tree links) with respect to a specific metric or to
      the TE metric used as the default metric when the metric is not
      specified.

   Processing these two objective functions is subject to the rules
   defined in [RFC5541].













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3.6.2.  METRIC Object-Type Values

   There are three types defined for the METRIC object in [RFC5440] --
   namely, the IGP metric, the TE metric, and Hop Counts.  This document
   defines three additional types for the METRIC object: the P2MP IGP
   metric, the P2MP TE metric, and the P2MP hop count metric.  They
   encode the sum of the metrics of all links of the tree.  The
   following values for these metric types have been assigned; see
   Section 6.4.

   o  P2MP IGP metric: T=8

   o  P2MP TE metric: T=9

   o  P2MP hop count metric: T=10

3.7.  Non-Support of P2MP Path Computation

   o  If a PCE receives a P2MP path computation request and it
      understands the P2MP flag in the RP object, but the PCE is not
      capable of P2MP computation, the PCE MUST send a PCErr message
      with a PCEP-ERROR object and corresponding Error-value.  The
      request MUST then be cancelled at the PCC.  The Error-Types and
      Error-values have been assigned; see Section 6 ("IANA
      Considerations") of this document.

   o  If the PCE does not understand the P2MP flag in the RP object,
      then the PCE would send a PCErr message with Error-Type=2
      (Capability not supported) as per [RFC5440].

3.8.  Non-Support by Back-Level PCE Implementations

   If a PCE receives a P2MP request and the PCE does not understand the
   P2MP flag in the RP object, and therefore the PCEP P2MP extensions,
   then the PCE SHOULD reject the request.

3.9.  P2MP TE Path Reoptimization Request

   A reoptimization request for a P2MP TE path is specified by the use
   of the R-bit within the RP object as defined in [RFC5440] and is
   similar to the reoptimization request for a P2P TE path.  The only
   difference is that the PCC MUST insert the list of Record Route
   Objects (RROs) and SRROs after each instance of the END-POINTS object
   in the PCReq message, as described in Section 3.4 ("Request Message
   Format") of this document.






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   An example of a reoptimization request and subsequent PCReq message
   is described below:

                        Common Header
                        RP with P2MP flag/R-bit set
                        END-POINTS for leaf type 3
                          RRO list
                        OF (optional)

            Figure 5: PCReq Message Example 1 for Optimization

   In this example, we request reoptimization of the path to all leaves
   without adding or pruning leaves.  The reoptimization request would
   use an END-POINTS object with leaf type 3.  The RRO list would
   represent the P2MP LSP before the optimization, and the modifiable
   path leaves would be indicated in the END-POINTS object.

   It is also possible to specify distinct leaves whose path cannot be
   modified.  An example of the PCReq message in this scenario would be:

                      Common Header
                      RP with P2MP flag/R-bit set
                      END-POINTS for leaf type 3
                        RRO list
                      END-POINTS for leaf type 4
                        RRO list
                      OF (optional)

            Figure 6: PCReq Message Example 2 for Optimization

3.10.  Adding and Pruning Leaves to/from the P2MP Tree

   When adding new leaves to or removing old leaves from the existing
   P2MP tree, by supplying a list of existing leaves, it is possible to
   optimize the existing P2MP tree.  This section explains the methods
   for adding new leaves to or removing old leaves from the existing
   P2MP tree.

   To add new leaves, the PCC MUST build a P2MP request using END-POINTS
   with leaf type 1.

   To remove old leaves, the PCC MUST build a P2MP request using
   END-POINTS with leaf type 2.  If no type-2 END-POINTS exist, then the
   PCE MUST send Error-Type 17, Error-value 1: the PCE cannot satisfy
   the request due to no END-POINTS with leaf type 2.






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   When adding new leaves to or removing old leaves from the existing
   P2MP tree, the PCC MUST also provide the list of old leaves, if any,
   including END-POINTS with leaf type 3, leaf type 4, or both.
   Specific PCEP-ERROR objects and types are used when certain
   conditions are not satisfied (i.e., when there are no END-POINTS with
   leaf type 3 or 4, or in the presence of END-POINTS with leaf type 1
   or 2).  A generic "Inconsistent END-POINTS" error will be used if a
   PCC receives a request that has an inconsistent END-POINTS setting
   (i.e., if a leaf specified as type 1 already exists).  These IANA
   assignments are documented in Section 6.6 ("PCEP-ERROR Objects and
   Types") of this document.

   For old leaves, the PCC MUST provide the old path as a list of RROs
   that immediately follows each END-POINTS object.  This document
   specifies Error-values when specific conditions are not satisfied.

   The following examples demonstrate full and partial reoptimization of
   existing P2MP LSPs:

   Case 1: Adding leaves with full reoptimization of existing paths

              Common Header
              RP with P2MP flag/R-bit set
              END-POINTS for leaf type 1
                RRO list
              END-POINTS for leaf type 3
                RRO list
              OF (optional)

   Case 2: Adding leaves with partial reoptimization of existing paths

              Common Header
              RP with P2MP flag/R-bit set
              END-POINTS for leaf type 1
              END-POINTS for leaf type 3
                RRO list
              END-POINTS for leaf type 4
                RRO list
              OF (optional)












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   Case 3: Adding leaves without reoptimization of existing paths

              Common Header
              RP with P2MP flag/R-bit set
              END-POINTS for leaf type 1
                RRO list
              END-POINTS for leaf type 4
                RRO list
              OF (optional)

   Case 4: Pruning leaves with full reoptimization of existing paths

              Common Header
              RP with P2MP flag/R-bit set
              END-POINTS for leaf type 2
                RRO list
              END-POINTS for leaf type 3
                RRO list
              OF (optional)

   Case 5: Pruning leaves with partial reoptimization of existing paths

              Common Header
              RP with P2MP flag/R-bit set
              END-POINTS for leaf type 2
                RRO list
              END-POINTS for leaf type 3
                RRO list
              END-POINTS for leaf type 4
                RRO list
              OF (optional)

   Case 6: Pruning leaves without reoptimization of existing paths

              Common Header
              RP with P2MP flag/R-bit set
              END-POINTS for leaf type 2
                RRO list
              END-POINTS for leaf type 4
                RRO list
              OF (optional)










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   Case 7: Adding and pruning leaves with full reoptimization of
           existing paths

              Common Header
              RP with P2MP flag/R-bit set
              END-POINTS for leaf type 1
              END-POINTS for leaf type 2
                RRO list
              END-POINTS for leaf type 3
                RRO list
              OF (optional)

   Case 8: Adding and pruning leaves with partial reoptimization of
           existing paths

              Common Header
              RP with P2MP flag/R-bit set
              END-POINTS for leaf type 1
              END-POINTS for leaf type 2
                RRO list
              END-POINTS for leaf type 3
                RRO list
              END-POINTS for leaf type 4
                RRO list
              OF (optional)

   Case 9: Adding and pruning leaves without reoptimization of existing
           paths

              Common Header
              RP with P2MP flag/R-bit set
              END-POINTS for leaf type 1
              END-POINTS for leaf type 2
                RRO list
              END-POINTS for leaf type 4
                RRO list
              OF (optional)














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3.11.  Discovering Branch Nodes

   Before computing the P2MP path, a PCE may need to be provided means
   to know which nodes in the network are capable of acting as branch
   LSRs.  A PCE can discover such capabilities by using the mechanisms
   defined in [RFC5073].

3.11.1.  Branch Node Object

   The PCC can specify a list of nodes that can be used as branch nodes
   or a list of nodes that cannot be used as branch nodes by using the
   Branch Node Capability (BNC) object.  The BNC object has the same
   format as the Include Route Object (IRO) as defined in [RFC5440],
   except that it only supports IPv4 and IPv6 prefix sub-objects.  Two
   Object-Type parameters are also defined:

   o  Branch node list: List of nodes that can be used as branch nodes.

   o  Non-branch node list: List of nodes that cannot be used as branch
      nodes.

   The object can only be carried in a PCReq message.  A path
   computation request may carry at most one Branch Node object.

   The Object-Class and Object-Type values have been allocated by IANA.
   The IANA assignments are documented in Section 6.5 ("PCEP Objects").

3.12.  Synchronization of P2MP TE Path Computation Requests

   There are cases when multiple P2MP LSPs' computations need to be
   synchronized.  For example, one P2MP LSP is the designated backup of
   another P2MP LSP.  In this case, path diversity for these dependent
   LSPs may need to be considered during the path computation.

   The synchronization can be done by using the existing SVEC
   functionality as defined in [RFC5440].















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   An example of synchronizing two P2MP LSPs, each having two leaves for
   Path Computation Request messages, is illustrated below:

                      Common Header
                      SVEC for sync of LSP1 and LSP2
                      OF (optional)
                      RP for LSP1
                        END-POINTS1 for LSP1
                        RRO1 list
                      RP for LSP2
                        END-POINTS2 for LSP2
                        RRO2 list

            Figure 7: PCReq Message Example for Synchronization

   This specification also defines two flags for the SVEC Object Flag
   Field for P2MP path-dependent computation requests.  The first flag
   allows the PCC to request that the PCE should compute a secondary
   P2MP path tree with partial path diversity for specific leaves or a
   specific S2L sub-path to the primary P2MP path tree.  The second flag
   allows the PCC to request that partial paths should be
   link direction diverse.

   The following flags are added to the SVEC object body in this
   document:

   o  P (Partial Path Diverse bit - 1 bit):

      When set, this would indicate a request for path diversity for a
      specific leaf, a set of leaves, or all leaves.

   o  D (Link Direction Diverse bit - 1 bit):

      When set, this would indicate a request that a partial path or
      paths should be link direction diverse.

   The IANA assignments are referenced in Section 6.8 of this document.

3.13.  Request and Response Fragmentation

   The total PCEP message length, including the common header, is
   16 bytes.  In certain scenarios, the P2MP computation request may not
   fit into a single request or response message.  For example, if a
   tree has many hundreds or thousands of leaves, then the request or
   response may need to be fragmented into multiple messages.






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   The F-bit is outlined in Section 3.3.1 ("The Extension of the RP
   Object") of this document.  The F-bit is used in the RP object to
   signal that the initial request or response was too large to fit into
   a single message and will be fragmented into multiple messages.  In
   order to identify the single request or response, each message will
   use the same request ID.

3.13.1.  Request Fragmentation Procedure

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

   The assumption is that request messages are reliably delivered and in
   sequence, since PCEP relies on TCP.

3.13.2.  Response Fragmentation Procedure

   Once the PCE computes a path based on the initial request, a response
   is sent back to the PCC.  If the response is too large to fit into a
   single response message, the PCE will split the response over
   multiple messages.  Each message sent by the PCE, except the last
   one, will have the F-bit set in the RP object to signify that the
   response has been fragmented into multiple messages.  In order to
   identify that a series of response messages represents a single
   response, each message will use the same response ID.

   Again, the assumption is that response messages are reliably
   delivered and in sequence, since PCEP relies on TCP.

3.13.3.  Fragmentation Example

   The following example illustrates the PCC sending a request message
   with Req-ID1 to the PCE, in order to add one leaf to an existing tree
   with 1200 leaves.  The assumption used for this example is that one
   request message can hold up to 800 leaves.  In this scenario, the
   original single message needs to be fragmented and sent using two
   smaller messages, which have Req-ID1 specified in the RP object, and
   with the F-bit set on the first message and the F-bit cleared on the
   second message.







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                 Common Header
                 RP1 with Req-ID1 and P2MP=1 and F-bit=1
                 OF (optional)
                 END-POINTS1 for P2MP
                   RRO1 list

                 Common Header
                 RP2 with Req-ID1 and P2MP=1 and F-bit=0
                 OF (optional)
                 END-POINTS1 for P2MP
                   RRO1 list

               Figure 8: PCReq Message Fragmentation Example

   To handle a scenario where the last fragmented message piece is lost,
   the receiver side of the fragmented message may start a timer once it
   receives the first piece of the fragmented message.  If the timer
   expires and it still has not received the last piece of the
   fragmented message, it should send an error message to the sender to
   signal that it has received an incomplete message.  The relevant
   error message is documented in Section 3.15 ("P2MP PCEP-ERROR Objects
   and Types").

3.14.  UNREACH-DESTINATION Object

   The PCE path computation request may fail because all or a subset of
   the destinations are unreachable.

   In such a case, the UNREACH-DESTINATION object allows the PCE to
   optionally specify the list of unreachable destinations.

   This object can be present in PCRep messages.  There can be up to one
   such object per RP.


















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   The following UNREACH-DESTINATION objects (for IPv4 and IPv6) are
   defined:

      UNREACH-DESTINATION Object-Class is 28.
      UNREACH-DESTINATION Object-Type for IPv4 is 1.
      UNREACH-DESTINATION Object-Type for IPv6 is 2.

   The format of the UNREACH-DESTINATION object body for IPv4
   (Object-Type=1) is as follows:

     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                  Destination IPv4 address                     |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ~                           ...                                 ~
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                  Destination IPv4 address                     |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

            Figure 9: UNREACH-DESTINATION Object Body for IPv4

   The format of the UNREACH-DESTINATION object body for IPv6
   (Object-Type=2) is as follows:

     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    |            Destination IPv6 address (16 bytes)                |
    |                                                               |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ~                          ...                                  ~
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    |              Destination IPv6 address (16 bytes)              |
    |                                                               |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

            Figure 10: UNREACH-DESTINATION Object Body for IPv6









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3.15.  P2MP PCEP-ERROR Objects and Types

   To indicate an error associated with a policy violation, the
   Error-value "P2MP Path computation is not allowed" has been added to
   the existing error code for Error-Type 5 ("Policy violation") as
   defined in [RFC5440] (see also Section 6.6 of this document):

      Error-Type=5; Error-value=7: if a PCE receives a P2MP path
      computation request that is not compliant with administrative
      privileges (i.e., "The PCE policy does not support P2MP path
      computation"), the PCE MUST send a PCErr message with a PCEP-ERROR
      object (Error-Type=5) and an Error-value of 7.  The corresponding
      P2MP path computation request MUST also be cancelled.

   To indicate capability errors associated with the P2MP path
   computation request, Error-Type (16) and subsequent Error-values are
   defined as follows for inclusion in the PCEP-ERROR object:

      Error-Type=16; Error-value=1: if a PCE receives a P2MP path
      computation request and the PCE is not capable of satisfying the
      request due to insufficient memory, the PCE MUST send a PCErr
      message with a PCEP-ERROR object (Error-Type=16) and an
      Error-value of 1.  The corresponding P2MP path computation request
      MUST also be cancelled.

      Error-Type=16; Error-value=2: if a PCE receives a P2MP path
      computation request and the PCE is not capable of P2MP
      computation, the PCE MUST send a PCErr message with a PCEP-ERROR
      object (Error-Type=16) and an Error-value of 2.  The corresponding
      P2MP path computation request MUST also be cancelled.

   To indicate P2MP message fragmentation errors associated with a P2MP
   path computation request, Error-Type (18) and subsequent Error-values
   are defined as follows for inclusion in the PCEP-ERROR object:

      Error-Type=18; Error-value=1: if a PCE has not received the last
      piece of the fragmented message, it should send an error message
      to the sender to signal that it has received an incomplete message
      (i.e., "Fragmented request failure").  The PCE MUST send a PCErr
      message with a PCEP-ERROR object (Error-Type=18) and an
      Error-value of 1.










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3.16.  PCEP NO-PATH Indicator

   To communicate the reasons for not being able to find a P2MP path
   computation, the NO-PATH object can be used in the PCRep message.

   One bit is defined in the NO-PATH-VECTOR TLV carried in the NO-PATH
   object:

      bit 24: when set, the PCE indicates that there is a reachability
      problem with all or a subset of the P2MP destinations.
      Optionally, the PCE can specify the destination or list of
      destinations that are not reachable using the UNREACH-DESTINATION
      object defined in Section 3.14.

4.  Manageability Considerations

   [RFC5862] describes various manageability requirements in support of
   P2MP path computation when applying PCEP.  This section describes how
   manageability requirements mentioned in [RFC5862] are supported in
   the context of PCEP extensions specified in this document.

   Note that [RFC5440] describes various manageability considerations
   for PCEP, and most of the manageability requirements mentioned in
   [RFC5862] are already covered there.

4.1.  Control of Function and Policy

   In addition to PCE configuration parameters listed in [RFC5440], the
   following additional parameters might be required:

   o  The PCE may be configured to enable or disable P2MP path
      computations.

   o  The PCE may be configured to enable or disable the advertisement
      of its P2MP path computation capability.  A PCE can advertise its
      P2MP capability via the IGP discovery mechanism discussed in
      Section 3.1.1 ("IGP Extensions for P2MP Capability Advertisement")
      or during the Open Message Exchange discussed in Section 3.1.2
      ("Open Message Extension").

4.2.  Information and Data Models

   A number of MIB objects have been defined in [RFC7420] for general
   PCEP control and monitoring of P2P computations.  [RFC5862] specifies
   that MIB objects will be required to support the control and
   monitoring of the protocol extensions defined in this document.  A
   new document will be required to define MIB objects for PCEP control
   and monitoring of P2MP computations.



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   The "ietf-pcep" PCEP YANG module is specified in [PCEP-YANG].  The
   P2MP capability of a PCEP entity or a configured peer can be set
   using this YANG module.  Also, support for P2MP path computation can
   be learned using this module.  The statistics are maintained in the
   "ietf-pcep-stats" YANG module as specified in [PCEP-YANG].  This YANG
   module will be required to be augmented to also include the
   P2MP-related statistics.

4.3.  Liveness Detection and Monitoring

   There are no additional considerations beyond those expressed in
   [RFC5440], since [RFC5862] does not address any additional
   requirements.

4.4.  Verifying Correct Operation

   There are no additional requirements beyond those expressed in
   [RFC4657] for verifying the correct operation of the PCEP sessions.
   It is expected that future MIB objects will facilitate verification
   of correct operation and reporting of P2MP PCEP requests, responses,
   and errors.

4.5.  Requirements for Other Protocols and Functional Components

   The method for the PCE to obtain information about a PCE capable of
   P2MP path computations via OSPF and IS-IS is discussed in
   Section 3.1.1 ("IGP Extensions for P2MP Capability Advertisement") of
   this document.

   The relevant IANA assignment is documented in Section 6.9 ("OSPF PCE
   Capability Flag") of this document.

4.6.  Impact on Network Operation

   It is expected that the use of PCEP extensions specified in this
   document will not significantly increase the level of operational
   traffic.  However, computing a P2MP tree may require more PCE state
   compared to a P2P computation.  In the event of a major network
   failure and multiple recovery P2MP tree computation requests being
   sent to the PCE, the load on the PCE may also be significantly
   increased.










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5.  Security Considerations

   As described in [RFC5862], P2MP path computation requests are more
   CPU-intensive and also utilize more link bandwidth.  In the event of
   an unauthorized P2MP path computation request or a denial-of-service
   attack, the subsequent PCEP requests and processing may be disruptive
   to the network.  Consequently, it is important that implementations
   conform to the relevant security requirements that specifically help
   to minimize or negate unauthorized P2MP path computation requests and
   denial-of-service attacks.  These mechanisms include the following:

   o  Securing the PCEP session requests and responses is RECOMMENDED
      using TCP security techniques such as the TCP Authentication
      Option (TCP-AO) [RFC5925] or using Transport Layer Security (TLS)
      [RFC8253], as per the recommendations and best current practices
      in [RFC7525].

   o  Authenticating the PCEP requests and responses to ensure that the
      message is intact and sent from an authorized node using the
      TCP-AO or TLS is RECOMMENDED.

   o  Policy control could be provided by explicitly defining which PCCs
      are allowed to send P2MP path computation requests to the PCE via
      IP access lists.

   PCEP operates over TCP, so it is also important to secure the PCE and
   PCC against TCP denial-of-service attacks.

   As stated in [RFC6952], PCEP implementations SHOULD support the
   TCP-AO [RFC5925] and not use TCP MD5 because of TCP MD5's known
   vulnerabilities and weakness.




















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6.  IANA Considerations

   IANA maintains a registry of PCEP parameters.  A number of IANA
   considerations have been highlighted in previous sections of this
   document.  IANA made the allocations as per [RFC6006].

6.1.  PCEP TLV Type Indicators

   As described in Section 3.1.2, the P2MP capability TLV allows the PCE
   to advertise its P2MP path computation capability.

   IANA had previously made an allocation from the "PCEP TLV Type
   Indicators" subregistry, where RFC 6006 was the reference.  IANA has
   updated the reference as follows to point to this document.

         Value       Description          Reference

         6           P2MP capable         RFC 8306

6.2.  Request Parameter Bit Flags

   As described in Section 3.3.1, three RP Object Flags have been
   defined.

   IANA had previously made allocations from the PCEP "RP Object Flag
   Field" subregistry, where RFC 6006 was the reference.  IANA has
   updated the reference as follows to point to this document.

         Bit      Description                         Reference

         18       Fragmentation (F-bit)               RFC 8306
         19       P2MP (N-bit)                        RFC 8306
         20       ERO-compression (E-bit)             RFC 8306

6.3.  Objective Functions

   As described in Section 3.6.1, this document defines two objective
   functions.

   IANA had previously made allocations from the PCEP "Objective
   Function" subregistry, where RFC 6006 was the reference.  IANA has
   updated the reference as follows to point to this document.

         Code Point        Name        Reference

         7                 SPT         RFC 8306
         8                 MCT         RFC 8306




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6.4.  METRIC Object-Type Values

   As described in Section 3.6.2, three METRIC object T fields have been
   defined.

   IANA had previously made allocations from the PCEP "METRIC Object
   T Field" subregistry, where RFC 6006 was the reference.  IANA has
   updated the reference as follows to point to this document.

         Value           Description               Reference

         8               P2MP IGP metric           RFC 8306
         9               P2MP TE metric            RFC 8306
         10              P2MP hop count metric     RFC 8306

6.5.  PCEP Objects

   As discussed in Section 3.3.2, two END-POINTS Object-Type values are
   defined.

   IANA had previously made the Object-Type allocations from the "PCEP
   Objects" subregistry, where RFC 6006 was the reference.  IANA has
   updated the reference as follows to point to this document.

         Object-Class Value    4
         Name                  END-POINTS
         Object-Type           3: IPv4
                               4: IPv6
                               5-15: Unassigned
         Reference             RFC 8306

   As described in Sections 3.2, 3.11.1, and 3.14, four PCEP
   Object-Class values and six PCEP Object-Type values have been
   defined.

   IANA had previously made allocations from the "PCEP Objects"
   subregistry, where RFC 6006 was the reference.  IANA has updated the
   reference to point to this document.













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   Also, for the following four PCEP objects, codepoint 0 for the
   Object-Type field is marked "Reserved", as per Erratum ID 4956 for
   RFC 5440.  IANA has updated the reference to point to this document.

         Object-Class Value    28
         Name                  UNREACH-DESTINATION
         Object-Type           0: Reserved
                               1: IPv4
                               2: IPv6
                               3-15: Unassigned
         Reference             RFC 8306

         Object-Class Value    29
         Name                  SERO
         Object-Type           0: Reserved
                               1: SERO
                               2-15: Unassigned
         Reference             RFC 8306

         Object-Class Value    30
         Name                  SRRO
         Object-Type           0: Reserved
                               1: SRRO
                               2-15: Unassigned
         Reference             RFC 8306

         Object-Class Value    31
         Name                  BNC
         Object-Type           0: Reserved
                               1: Branch node list
                               2: Non-branch node list
                               3-15: Unassigned
         Reference             RFC 8306


















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6.6.  PCEP-ERROR Objects and Types

   As described in Section 3.15, a number of PCEP-ERROR Object
   Error-Types and Error-values have been defined.

   IANA had previously made allocations from the PCEP "PCEP-ERROR Object
   Error Types and Values" subregistry, where RFC 6006 was the
   reference.  IANA has updated the reference as follows to point to
   this document.

   Error
   Type  Meaning                                            Reference

   5     Policy violation
           Error-value=7:                                  RFC 8306
             P2MP Path computation is not allowed

   16    P2MP Capability Error
           Error-value=0: Unassigned                       RFC 8306
           Error-value=1:                                  RFC 8306
             The PCE cannot satisfy the request
             due to insufficient memory
           Error-value=2:                                  RFC 8306
             The PCE is not capable of P2MP computation

   17    P2MP END-POINTS Error
           Error-value=0: Unassigned                       RFC 8306
           Error-value=1:                                  RFC 8306
             The PCE cannot satisfy the request
             due to no END-POINTS with leaf type 2
           Error-value=2:                                  RFC 8306
             The PCE cannot satisfy the request
             due to no END-POINTS with leaf type 3
           Error-value=3:                                  RFC 8306
             The PCE cannot satisfy the request
             due to no END-POINTS with leaf type 4
           Error-value=4:                                  RFC 8306
             The PCE cannot satisfy the request
             due to inconsistent END-POINTS

   18    P2MP Fragmentation Error
           Error-value=0: Unassigned                       RFC 8306
           Error-value=1:                                  RFC 8306
             Fragmented request failure







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6.7.  PCEP NO-PATH Indicator

   As discussed in Section 3.16, the NO-PATH-VECTOR TLV Flag Field has
   been defined.

   IANA had previously made an allocation from the PCEP "NO-PATH-VECTOR
   TLV Flag Field" subregistry, where RFC 6006 was the reference.  IANA
   has updated the reference as follows to point to this document.

         Bit    Description                               Reference

         24     P2MP Reachability Problem                 RFC 8306

6.8.  SVEC Object Flag

   As discussed in Section 3.12, two SVEC Object Flags are defined.

   IANA had previously made allocations from the PCEP "SVEC Object Flag
   Field" subregistry, where RFC 6006 was the reference.  IANA has
   updated the reference as follows to point to this document.

         Bit      Description                              Reference

         19       Partial Path Diverse                     RFC 8306
         20       Link Direction Diverse                   RFC 8306

6.9.  OSPF PCE Capability Flag

   As discussed in Section 3.1.1, the OSPF Capability Flag is defined to
   indicate P2MP path computation capability.

   IANA had previously made an assignment from the OSPF Parameters "Path
   Computation Element (PCE) Capability Flags" registry, where RFC 6006
   was the reference.  IANA has updated the reference as follows to
   point to this document.

         Bit      Description                              Reference

         10       P2MP path computation                    RFC 8306












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7.  References

7.1.  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>.

   [RFC3473]  Berger, L., Ed., "Generalized Multi-Protocol Label
              Switching (GMPLS) Signaling Resource ReserVation
              Protocol-Traffic Engineering (RSVP-TE) Extensions",
              RFC 3473, DOI 10.17487/RFC3473, January 2003,
              <https://www.rfc-editor.org/info/rfc3473>.

   [RFC4873]  Berger, L., Bryskin, I., Papadimitriou, D., and A. Farrel,
              "GMPLS Segment Recovery", RFC 4873, DOI 10.17487/RFC4873,
              May 2007, <https://www.rfc-editor.org/info/rfc4873>.

   [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>.

   [RFC5073]  Vasseur, J., Ed., and J. Le Roux, Ed., "IGP Routing
              Protocol Extensions for Discovery of Traffic Engineering
              Node Capabilities", RFC 5073, DOI 10.17487/RFC5073,
              December 2007, <https://www.rfc-editor.org/info/rfc5073>.

   [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>.






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   [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>.

   [RFC5541]  Le Roux, JL., Vasseur, JP., and Y. Lee, "Encoding of
              Objective Functions in the Path Computation Element
              Communication Protocol (PCEP)", RFC 5541,
              DOI 10.17487/RFC5541, June 2009,
              <https://www.rfc-editor.org/info/rfc5541>.

   [RFC7770]  Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and
              S. Shaffer, "Extensions to OSPF for Advertising Optional
              Router Capabilities", RFC 7770, DOI 10.17487/RFC7770,
              February 2016, <https://www.rfc-editor.org/info/rfc7770>.

   [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>.

7.2.  Informative References

   [PCEP-YANG]
              Dhody, D., Ed., 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-05, July 2017.

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

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








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   [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>.

   [RFC5862]  Yasukawa, S. and A. Farrel, "Path Computation Clients
              (PCC) - Path Computation Element (PCE) Requirements for
              Point-to-Multipoint MPLS-TE", RFC 5862,
              DOI 10.17487/RFC5862, June 2010,
              <https://www.rfc-editor.org/info/rfc5862>.

   [RFC5925]  Touch, J., Mankin, A., and R. Bonica, "The TCP
              Authentication Option", RFC 5925, DOI 10.17487/RFC5925,
              June 2010, <https://www.rfc-editor.org/info/rfc5925>.

   [RFC6006]  Zhao, Q., Ed., King, D., Ed., Verhaeghe, F., Takeda, T.,
              Ali, Z., and J. Meuric, "Extensions to the Path
              Computation Element Communication Protocol (PCEP) for
              Point-to-Multipoint Traffic Engineering Label Switched
              Paths", RFC 6006, DOI 10.17487/RFC6006, September 2010,
              <https://www.rfc-editor.org/info/rfc6006>.

   [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/info/rfc6952>.

   [RFC7420]  Koushik, A., Stephan, E., Zhao, Q., King, D., and J.
              Hardwick, "Path Computation Element Communication Protocol
              (PCEP) Management Information Base (MIB) Module",
              RFC 7420, DOI 10.17487/RFC7420, December 2014,
              <https://www.rfc-editor.org/info/rfc7420>.

   [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>.

   [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>.





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Appendix A.  Summary of Changes from RFC 6006

   o  Updated the text to use the term "PCC" instead of "user" while
      describing the encoding rules in Section 3.10.

   o  Updated the example in Figure 7 to explicitly include the
      RP object.

   o  Corrected the description of the F-bit in the RP object in
      Section 3.13, as per Erratum ID 3836.

   o  Corrected the description of the fragmentation procedure for the
      response in Section 3.13.2, as per Erratum ID 3819.

   o  Corrected the Error-Type for fragmentation in Section 3.15, as per
      Erratum ID 3830.

   o  Updated the references for the OSPF Router Information Link State
      Advertisement (LSA) [RFC7770] and the PCEP MIB [RFC7420].

   o  Added current information and references for PCEP YANG [PCEP-YANG]
      and PCEPS [RFC8253].

   o  Updated the Security Considerations section to include the TCP-AO
      and TLS.

   o  Updated the IANA Considerations section (Section 6.5) to mark
      codepoint 0 as "Reserved" for the Object-Type defined in this
      document, as per Erratum ID 4956 for [RFC5440].  IANA references
      have also been updated to point to this document.

Appendix A.1.  RBNF Changes from RFC 6006

   o  Updates to the RBNF for the request message format, per
      Erratum ID 4867:

      *  Updated the request message to allow for the bundling of
         multiple path computation requests within a single PCReq
         message.

      *  Added <svec-list> in PCReq messages.  This object was missed in
         [RFC6006].

      *  Added the BNC object in PCReq messages.  This object is
         required to support P2MP.  The BNC object shares the same
         format as the IRO, but it only supports IPv4 and IPv6 prefix
         sub-objects.




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      *  Updated the <RRO-List> format to also allow the SRRO.  This
         object was missed in [RFC6006].

      *  Removed the BANDWIDTH object followed by the RRO from
         <RRO-List>.  The BANDWIDTH object was included twice in
         RFC 6006 -- once as part of <end-point-path-pair-list> and also
         as part of <RRO-List>.  The latter has been removed, and the
         RBNF is backward compatible with [RFC5440].

      *  Updated the <end-point-rro-pair-list> to allow an optional
         BANDWIDTH object only if <RRO-List> is included.

   o  Updates to the RBNF for the reply message format, per
      Erratum ID 4868:

      *  Updated the reply message to allow for bundling of multiple
         path computation replies within a single PCRep message.

      *  Added the UNREACH-DESTINATION object in PCRep messages.  This
         object was missed in [RFC6006].































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Acknowledgements

   The authors would like to thank Adrian Farrel, Young Lee, Dan Tappan,
   Autumn Liu, Huaimo Chen, Eiji Oki, Nic Neate, Suresh Babu K, Gaurav
   Agrawal, Vishwas Manral, Dan Romascanu, Tim Polk, Stewart Bryant,
   David Harrington, and Sean Turner for their valuable comments and
   input on this document.

   Thanks to Deborah Brungard for handling related errata for RFC 6006.

   The authors would like to thank Jonathan Hardwick and Adrian Farrel
   for providing review comments with suggested text for this document.

   Thanks to Jonathan Hardwick for being the document shepherd and for
   providing comments and guidance.

   Thanks to Ben Niven-Jenkins for RTGDIR reviews.

   Thanks to Roni Even for GENART reviews.

   Thanks to Fred Baker for the OPSDIR review.

   Thanks to Deborah Brungard for being the responsible AD and guiding
   the authors.

   Thanks to Mirja Kuehlewind, Alvaro Retana, Ben Campbell, Adam Roach,
   Benoit Claise, Suresh Krishnan, and Eric Rescorla for their IESG
   review and comments.























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Contributors

   Fabien Verhaeghe
   Thales Communication France
   160 boulevard Valmy
   92700 Colombes
   France
   Email: fabien.verhaeghe@gmail.com

   Tomonori Takeda
   NTT Corporation
   3-9-11, Midori-Cho
   Musashino-Shi, Tokyo  180-8585
   Japan
   Email: tomonori.takeda@ntt.com

   Zafar Ali
   Cisco Systems, Inc.
   2000 Innovation Drive
   Kanata, Ontario  K2K 3E8
   Canada
   Email: zali@cisco.com

   Julien Meuric
   Orange
   2, Avenue Pierre Marzin
   22307 Lannion Cedex
   France
   Email: julien.meuric@orange.com

   Jean-Louis Le Roux
   Orange
   2, Avenue Pierre Marzin
   22307 Lannion Cedex
   France
   Email: jeanlouis.leroux@orange.com

   Mohamad Chaitou
   France
   Email: mohamad.chaitou@gmail.com

   Udayasree Palle
   Huawei Technologies
   Divyashree Techno Park, Whitefield
   Bangalore, Karnataka  560066
   India
   Email: udayasreereddy@gmail.com




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Authors' Addresses

   Quintin Zhao
   Huawei Technologies
   125 Nagog Technology Park
   Acton, MA  01719
   United States of America

   Email: quintin.zhao@huawei.com


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

   Email: dhruv.ietf@gmail.com


   Ramanjaneya Reddy Palleti
   Huawei Technologies
   Divyashree Techno Park, Whitefield
   Bangalore, Karnataka  560066
   India

   Email: ramanjaneya.palleti@huawei.com


   Daniel King
   Old Dog Consulting
   United Kingdom

   Email: daniel@olddog.co.uk

















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