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PCE Working Group                                                H. Chen
Internet-Draft                                                  D. Dhody
Intended status: Standards Track                     Huawei Technologies
Expires: October 31, 2018                                 April 29, 2018


       A Forward-Search P2MP TE LSP Inter-Domain Path Computation
               draft-chen-pce-forward-search-p2mp-path-14

Abstract

   This document presents a forward search procedure for computing a
   path for a Point-to-MultiPoint (P2MP) Traffic Engineering (TE) Label
   Switched Path (LSP) crossing a number of domains through using
   multiple Path Computation Elements (PCEs).  In addition, extensions
   to the Path Computation Element Communication Protocol (PCEP) for
   supporting the forward search procedure are described.

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on October 31, 2018.

Copyright Notice

   Copyright (c) 2018 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
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   include Simplified BSD License text as described in Section 4.e of




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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Conventions Used in This Document . . . . . . . . . . . . . .   4
   4.  Requirements  . . . . . . . . . . . . . . . . . . . . . . . .   4
   5.  Forward Search P2MP Path Computation  . . . . . . . . . . . .   4
     5.1.  Overview of Procedure . . . . . . . . . . . . . . . . . .   5
     5.2.  Description of Procedure  . . . . . . . . . . . . . . . .   5
     5.3.  Processing Request and Reply Messages . . . . . . . . . .   8
   6.  Comparing to BRPC . . . . . . . . . . . . . . . . . . . . . .   9
   7.  Extensions to PCEP  . . . . . . . . . . . . . . . . . . . . .   9
     7.1.  RP Object Extension . . . . . . . . . . . . . . . . . . .  10
     7.2.  PCE Object  . . . . . . . . . . . . . . . . . . . . . . .  10
     7.3.  Candidate Node List Object  . . . . . . . . . . . . . . .  11
     7.4.  Node Flags Object . . . . . . . . . . . . . . . . . . . .  12
     7.5.  Request Message Extension . . . . . . . . . . . . . . . .  12
     7.6.  Reply Message Extension . . . . . . . . . . . . . . . . .  13
   8.  Security  Considerations  . . . . . . . . . . . . . . . . . .  14
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  14
     9.1.  Request Parameter Bit Flags . . . . . . . . . . . . . . .  14
   10. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . .  14
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  14
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  14
     11.2.  Informative References . . . . . . . . . . . . . . . . .  15
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  15

1.  Introduction

   RFC 4105 "Requirements for Inter-Area MPLS TE" lists the requirements
   for computing a shortest path for a TE LSP crossing multiple IGP
   areas; and RFC 4216 "MPLS Inter-Autonomous System (AS) TE
   Requirements" describes the requirements for computing a shortest
   path for a TE LSP crossing multiple ASes.  RFC 5671 "Applicability of
   PCE to P2MP MPLS and GMPLS TE" examines the applicability of PCE to
   path computation for P2MP TE LSPs in MPLS and GMPLS networks.

   This document presents a forward search procedure to address these
   requirements for computing a path for a P2MP TE LSP crossing domains
   through using multiple Path Computation Elements (PCEs).

   The procedure is called "Forward Search Shortest P2MP LSP Path
   Crossing Domains" or FSPC for short.  The major characteristics of
   this procedure for computing a path for a P2MP TE LSP from a source




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   node to a number of destination nodes crossing multiple domains
   include the following three ones.

   1.  It guarantees that the path computed from the source node to the
       destination nodes is shortest.

   2.  It does not depend on any domain path tree or domain sequences
       from the source node to the destination nodes.

   3.  Navigating a mesh of domains is simple and efficient.

2.  Terminology

   ABR: Area Border Router.  Routers used to connect two IGP areas
   (areas in OSPF or levels in IS-IS).

   ASBR: Autonomous System Border Router.  Routers used to connect
   together ASes of the same or different service providers via one or
   more inter-AS links.

   Boundary Node (BN): a boundary node is either an ABR in the context
   of inter-area Traffic Engineering or an ASBR in the context of inter-
   AS Traffic Engineering.

   Entry BN of domain(n): a BN connecting domain(n-1) to domain(n) along
   the path found from the source node to the BN, where domain(n-1) is
   the previous hop domain of domain(n).

   Exit BN of domain(n): a BN connecting domain(n) to domain(n+1) along
   the path found from the source node to the BN, where domain(n+1) is
   the next hop domain of domain(n).

   Inter-area TE LSP: A TE LSP that crosses an IGP area boundary.

   Inter-AS TE LSP: A TE LSP that crosses an AS boundary.

   LSP: Label Switched Path.

   LSR: Label Switching Router.

   PCC: Path Computation Client.  Any client application requesting a
   path computation to be performed by a Path Computation Element.

   PCE: Path Computation Element.  An entity (component, application, or
   network node) that is capable of computing a network path or route
   based on a network graph and applying computational constraints.

   PCE(i) is a PCE with the scope of domain(i).



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   TED: Traffic Engineering Database.

   This document uses terminologies defined in RFC5440.

3.  Conventions Used in This Document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC2119.

4.  Requirements

   This section summarizes the requirements specific for computing a
   path for a Traffic Engineering (TE) LSP crossing multiple domains
   (areas or ASes).  More requirements for Inter-Area and Inter-AS MPLS
   Traffic Engineering are described in RFC 4105 and RFC 4216.

   A number of requirements specific for a solution to compute a path
   for a TE LSP crossing multiple domains is listed as follows:

   1.  The solution SHOULD provide the capability to compute a shortest
       path dynamically, satisfying a set of specified constraints
       across multiple IGP areas.

   2.  The solution MUST provide the ability to reoptimize in a
       minimally disruptive manner (make before break) an inter-area TE
       LSP, should a more optimal path appear in any traversed IGP area.

   3.  The solution SHOULD provide mechanism(s) to compute a shortest
       end-to-end path for a TE LSP crossing multiple ASes and
       satisfying a set of specified constraints dynamically.

   4.  Once an inter-AS TE LSP has been established, and should there be
       any resource or other changes inside anyone of the ASes, the
       solution MUST be able to re-optimize the LSP accordingly and non-
       disruptively, either upon expiration of a configurable timer or
       upon being triggered by a network event or a manual request at
       the TE tunnel Head-End.

5.  Forward Search P2MP Path Computation

   This section gives an overview of the forward search path computation
   procedure (FSPC) to satisfy the requirements for computing a path for
   a P2MP TE LSP crossing multiple domains described above and describes
   the procedure in details.






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5.1.  Overview of Procedure

   Simply speaking, the idea of FSPC for computing a path for an MPLS TE
   P2MP LSP crossing multiple domains from a source node to a number of
   destination nodes includes:

   Start from the source node and the source domain.

   Consider the optimal path segment from the source node to every exit
   boundary and destination node of the source domain as a special link;

   Consider the optimal path segment from an entry boundary node to
   every exit boundary node and destination node of a domain as a
   special link; and the optimal path segment is computed as needed.

   The whole topology consisting of many domains can be considered as a
   special virtual topology, which contains those special links and the
   inter-domain links.

   Compute a shortest path in this special topology from the source node
   to the multiple destination nodes using CSPF.

   FSPC running at any PCE just grows the result path list/tree in the
   same way as normal CSPF on the special virtual topology.  When the
   result path list/tree reaches all the destination nodes, the shortest
   path from the source node to the destination nodes is found and a
   PCRep message with the path is sent to the PCE/PCC that sends the
   PCReq message eventually.

5.2.  Description of Procedure

   Suppose that we have the following variables:

   A current PCE named as CurrentPCE which is currently computing the
   path.

   A candidate node list named as CandidateNodeList, which contains the
   nodes to each of which the temporary optimal path from the source
   node is currently found and satisfies a set of given constraints.
   Each node C in CandidateNodeList has the following information:

   o  the cost of the path from the source node to node C,

   o  the previous hop node P and the link between P and C,

   o  the PCE responsible for C (i.e., the PCE responsible for the
      domain containing C.  Alternatively, we may use the domain instead
      of the PCE.), and



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   o  the flags for C.

   The flags include:

   o  bit D indicating that C is a Destination node if it is set;

   o  bit S indicating that C is the Source node if it is set;

   o  bit E indicating that C is an Exit boundary node if it is set;

   o  bit I indicating that C is an entry boundary node if it is set;
      and

   o  bit T indicating that C is on result path Tree if it is set.

   The nodes in CandidateNodeList are ordered by path cost.

   Initially, CandidateNodeList contains a Source Node, with path cost
   0, PCE responsible for the source domain, and flags with S bit set.
   It also contains every destination node, with path cost infinity and
   flags with D bit set.

   A result path list or tree named as ResultPathTree, which contains
   the shortest paths from the source node to the boundary nodes and
   destination nodes.  Initially, ResultPathTree is empty.

   Alternatively, the result path list or tree can be combined into the
   candidate node list.  We may set bit T to one in the node flags for
   the candidate node when grafting it into the existing result path
   list or tree.  Thus all the candidate nodes with bit T set to one in
   the candidate list constitute the result path tree or list.

   FSPC for computing a path for an MPLS TE P2MP LSP crossing a number
   of domains from a source node to a number of destination nodes can be
   described as follows:

   Initially, a PCC sends a PCE responsible for the source domain a
   request with CandidateNodeList and ResultPathTree initialized.

   When the PCE responsible for a domain (called current domain)
   receives a request for computing the path for the MPLS TE P2MP LSP,
   it checks whether the current PCE is the PCE responsible for the node
   C with the minimum cost in the CandidateNodeList.  If it is, then
   remove C from CandidateNodeList and graft it into ResultPathTree
   (i.e., set flag bit T of node C to one); otherwise, a PCReq message
   is sent to the PCE for node C.





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   Suppose that node C is in the current domain.  The ResultPathTree is
   built from C in the following steps.

   If node C is a destination node (i.e., the Destination Node (D) bit
   in the Flags is set), then check whether the path cost to node C is
   infinity.  If it is, then we can not find any path for the P2MP LSP,
   and a repply message with failure reasons is sent; otherwise, if all
   the destinations are on the result path tree, then the shortest path
   is found and a PCRep message with the path is sent to the PCE/PCC
   which sends the request to the current PCE.

   If node C is an entry boundary node or the source node, then the
   optimal path segments from node C to every destination node and every
   exit boundary node of the current domain that is not on the result
   path tree and satisfies the given constraints are computed through
   using CSPF and as special links.

   For every node N connected to node C through a special link (i.e.,
   the optimal path segment satisfying the given constraints), it is
   merged into CandidateNodeList.  The cost to node N is the sum of the
   cost to node C and the cost of the special link (i.e., the path
   segment) between C and N.  If node N is not in the candidate node
   list, then node N is added into the list with the cost to node N,
   node C as its previous hop node and a PCE for node N.  The PCE for
   node N is the current PCE if node N is an ASBR; otherwise (node N is
   an ABR, an exit boundary node of the current domain and an entry
   boundary node of the domain next to the current domain) the PCE for
   node N is the PCE for the next domain.  If node N is in the candidate
   node list and the cost to node N through node C is less than the cost
   to node N in the list, then replace the cost to node N in the list
   with the cost to node N through node C and the previous hop to node N
   in the list with node C.

   If node C is an exit boundary node and there are inter-domain links
   connecting to it (i.e., node C is an ASBR) and satisfying the
   constraints, then for every node N connecting to C, satisfying the
   constraints and not on the result path tree, it is merged into the
   candidate node list.  The cost to node N is the sum of the cost to
   node C and the cost of the link between C and N.  If node N is not in
   the candidate node list, then node N is added into the list with the
   cost to node N, node C as its previous hop node and the PCE for node
   N.  If node N is in the candidate node list and the cost to node N
   through node C is less than the cost to node N in the list, then
   replace the cost to node N in the list with the cost to node N
   through node C and the previous hop to node N in the list with node
   C.





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   If the CurrentPCE is the same as the PCE for the node D with the
   minimum cost in CandidateNodeList, then the node D is removed from
   CandidateNodeList and grafted to ResultPathTree (i.e., set flag bit T
   of node D to one), and the above steps are repeated; otherwise, a
   request message is to be sent to the PCE for node D.

5.3.  Processing Request and Reply Messages

   In this section, we describe the processing of the request and reply
   messages with Forward search bit set for FSPC.  Each of the request
   and reply messages mentioned below has its Forward search bit set
   even though we do not indicate this explicitly.

   In the case that a reply message is a final reply, which contains the
   optimal path from the source to the destination, the reply message is
   sent toward the PCC along the path that the request message goes from
   the PCC to the current PCE in reverse direction.

   In the case that a request message is to be sent to the PCE for node
   D with the minimum cost in the candidate node list and there is a PCE
   session between the current domain and the next domain containing
   node D, the current PCE sends the PCE for node D through the session
   a request message with the source node, the destination node,
   CandidateNodeList and ResultPathTree.

   In the case that a request message is to be sent to the PCE for node
   D and there is not any PCE session between the current PCE and the
   PCE for node D, a reply message is sent toward a branch point on the
   result path tree from the current domain along the path that the
   request message goes from the PCC to the current PCE in reverse
   direction.  From the branch point, there is a downward path to the
   domain containing the previous hop node of node D on the result path
   tree and to the domain containing node D.  At this branch point, the
   request message is sent to the PCE for node D along the downward
   path.

   Suppose that node D has the minimum cost in CandidateNodeList when a
   PCE receives a request message or a reply message containing
   CandidateNodeList.

   When a PCE (current PCE) for a domain (current domain) receives a
   reply message PCRep, it checks whether the reply is a final reply
   with the optimal path from the source to the destination.  If the
   reply is the final reply, the current PCE sends the reply to the PCE
   that sends the request to the current PCE; otherwise, it checks
   whether there is a path from the current domain to the domain
   containing the previous hop node of node D on ResultPathTree and to
   the domain containing node D.  If there is a path, the PCE sends a



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   request PCReq to the PCE responsible for the next domain along the
   path; otherwise, it sends a reply PCRep to the PCE that sends the
   request to the current PCE.

   When a PCE receives a request PCReq, it checks whether the current
   domain contains node D.  If it does, then node D is removed from
   CandidateNodeList and grafted to ResultPathTree (i.e., set flag bit T
   of node D to one), and the above steps in the previous sub section
   are repeated; otherwise, the PCE sends a request PCReq to the PCE
   responsible for the next domain along the path from the current
   domain to the domain containing the previous hop node of node D on
   ResultPathTree and to the domain containing node D.

6.  Comparing to BRPC

   RFC 5441 describes the Backward Recursive Path Computation (BRPC)
   algorithm or procedure for computing an MPLS TE P2P LSP path from a
   source node to a destination node crossing multiple domains.
   Comparing to BRPC, there are a number of differences between BRPC and
   the Forward-Search P2MP TE LSP Inter-Domain Path Computation (FSPC).
   Some of the differences are briefed below.

   At first, BRPC is for computing a shortest path from a source node to
   a destination node crossing multiple domains.  FSPC is for computing
   a shortest path from a source node to a number of destination nodes
   crossing multiple domains.

   Secondly, for BRPC to compute a shortest path from a source node to a
   destination node crossing multiple domains, we MUST provide a
   sequence of domains from the source node to the destination node to
   BRPC in advance.  FSPC does not need any sequence of domains for
   computing a shortest inter-domain P2MP path.

   Moreover, for a given sequence of domains domain(1), domain(2), ... ,
   domain(n), BRPC searches the shortest path from domain(n), to
   domain(n-1), until domain(1).  Thus it is hard for BRPC to be
   extended for computing a shortest path from a source node to a number
   of destination nodes crossing multiple domains.  FSPC calculates a
   shortest path in a special topology from the source node to the
   destination nodes using CSPF.

7.  Extensions to PCEP

   The extensions to PCEP for FSPC include the definition of a new flag
   in the RP object, a result path list/tree and a candidate node list
   in a request message.





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7.1.  RP Object Extension

   The following flag is added into the RP Object:

   The F bit is added in the flag bits field of the RP object to tell
   the receiver of the message that the request/reply is for FSPC.

     o F (FSPC bit - 1 bit):
         0: This indicates that this is not PCReq/PCRep for FSPC.
         1: This indicates that this is PCReq or PCRep message for FSPC.


   The T bit is added in the flag bits field of the RP object to tell
   the receiver of the message that the reply is for transferring a
   request message to the domain containing the node with minimum cost
   in the candidate list.

       o T (Transfer request bit - 1 bit):
           0: This indicates that this is not a PCRep
              for transferring a request message.
           1: This indicates that this is a PCRep message
              for transferring a request message.


   Setting Transfer request T-bit in a RP Object to one indicates that a
   reply message containing the RP Object is for transferring a request
   message to the domain containing the node with minimum cost in the
   candidate list.

   The IANA request is referenced in Section below (Request Parameter
   Bit Flags) of this document.

   This F bit with the N bit defined in RFC6006 can indicate whether the
   request/reply is for FSPC of an MPLS TE P2MP LSP or an MPLS TE P2P
   LSP.

       o F = 1 and N = 1: This indicates that this is a PCReq/PCRep
                          message for FSPC of an MPLS TE P2MP LSP.
       o F = 1 and N = 0: This indicates that this is a PCReq/PCRep
                          message for FSPC of an MPLS TE P2P LSP.


7.2.  PCE Object

   The figure below illustrates a PCE IPv4 object body (Object-Type=1),
   which comprises a PCE IPv4 address.  The PCE IPv4 address object
   indicates the IPv4 address of a PCE , with which a PCE session may be
   established and to which a request message may be sent.



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        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                       PCE  IPv4 address                       |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   The format of the PCE 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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       |                 PCE  IPv6 address (16 bytes)                  |
       |                                                               |
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


7.3.  Candidate Node List Object

   The candidate-node-list-obj object contains a list of candidate
   nodes.  A new PCEP object class and type are requested for it.  The
   format of the candidate-node-list-obj object body 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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      //                     <candidate-node-list>                   //
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   The following is the definition of the candidate node list.

         <candidate-node-list>::= <candidate-node>
                                  [<candidate-node-list>]
         <candidate-node>::= <ERO>
                             <candidate-attribute-list>

         <candidate-attribute-list>::= [<attribute-list>]
                                       [<PCE>]
                                       [<Node-Flags>]






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   The ERO in a candidate node contain just the path segment of the last
   link of the path, which is from the previous hop node of the tail end
   node of the path to the tail end node.  With this information, we can
   graft the candidate node into the existing result path list or tree.

   Simply speaking, a candidate node has the same or similar format of a
   path defined in RFC 5440, but the ERO in the candidate node just
   contain the tail end node of the path and its previous hop, and the
   candidate node may contain two new objects PCE and node flags.

7.4.  Node Flags Object

   The Node Flags object is used to indicate the characteristics of the
   node in a candidate node list in a request or reply message for FSPC.
   The Node Flags object comprises a Reserved field, and a number of
   Flags.

   The format of the Node Flags object body 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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |D|S|I|E|N|          Flags      |         Reserved              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   where

       o D = 1:  The node is a destination node.
       o S = 1:  The node is a source node.
       o I = 1:  The node is an entry boundary node.
       o E = 1:  The node is an exit boundary node.
       o T = 1:  The node is on the result path tree.


7.5.  Request Message Extension

   Below is the message format for a request message with the extension
   of a result path list and a candidate node list:












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        <PCReq Message>::= <Common Header>
                           <request>
        <request>::= <RP> <END-POINT-RRO-PAIR-LIST>  [<OF>]  [<LSPA>]
                     [<BANDWIDTH>]  [<metric-list>]  [<RRO>[<BANDWIDTH>]]
                     [<IRO>] [<LOAD-BALANCING>]
                     [<result-path-list>]
                     [<candidate-node-list-obj>]
     where:
        <result-path-list>::=<path>[<result-path-list>]
        <path>::= <ERO><attribute-list>
        <attribute-list>::=[<LSPA>]  [<BANDWIDTH>]  [<metric-list>]
                           [<IRO>]

        <candidate-node-list-obj> contains a <candidate-node-list>

        <candidate-node-list>::= <candidate-node>
                                 [<candidate-node-list>]
        <candidate-node>::= <ERO>
                            <candidate-attribute-list>

        <candidate-attribute-list>::= [<attribute-list>]
                                      [<PCE>]
                                      [<Node-Flags>]


                Figure 1: The Format for a Request Message

   The definition for the result path list that may be added into a
   request message is the same as that for the path list in a reply
   message that is described in RFC5440.

7.6.  Reply Message Extension

   Below is the message format for a reply message with the extension of
   a result path list and a candidate node list:

           <PCRep Message> ::= <Common Header>
                               <response>
           <response> ::= <RP>  [<END-POINT-PATH-PAIR-LIST>]
                          [<NO-PATH>] [<attribute-list>]
                          [<result-path-list>]
                          [<candidate-node-list-obj>]
        where:
           <candidate-node-list-obj> contains a <candidate-node-list>


   If the path from the source to the destinations is not found yet and
   there are still chances to find a path (i.e., the candidate list is



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   not empty), the reply message contains candidate-node-list-obj
   consisting of the information of the candidate list, which is
   encoded.  In this case, the Transfer request T-bit in the RP Object
   is set to one.

   If the path from the source to the destination is found, the reply
   message contains path-list comprising the information of the path.

8.  Security Considerations

   The mechanism described in this document does not raise any new
   security issues for the PCEP protocols.

9.  IANA Considerations

   This section specifies requests for IANA allocation.

9.1.  Request Parameter Bit Flags

   A new RP Object Flag has been defined in this document.  IANA is
   requested to make the following allocation from the "PCEP RP Object
   Flag Field" Sub-Registry:

         Bit       Description                         Reference
          18       FSPC (F-bit)                        This I-D
          19       Transfer Request         (T-bit)    This I-D


10.  Acknowledgement

   The author would like to thank Julien Meuric, Daniel King, Cyril
   Margaria, Ramon Casellas, Olivier Dugeon and Oscar Gonzalez de Dios
   for their valuable comments on this draft.

11.  References

11.1.  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>.




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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>.

   [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>.

11.2.  Informative References

   [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>.

   [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>.

Authors' Addresses

   Huaimo Chen
   Huawei Technologies
   Boston, MA
   USA

   EMail: Huaimo.chen@huawei.com


   Dhruv Dhody
   Huawei Technologies
   Leela Palace
   Bangalore, Karnataka  560008
   INDIA

   EMail: dhruv.dhody@huawei.com









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