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Versions: (draft-vasseur-pce-brpc) 00 01 02 03 04 05 06 07 08 09 RFC 5441

Networking Working Group                                JP. Vasseur, Ed.
Internet-Draft                                        Cisco Systems, Inc
Intended status: Standards Track                                R. Zhang
Expires: October 16, 2008                                     BT Infonet
                                                                N. Bitar
                                                                 Verizon
                                                             JL. Le Roux
                                                          France Telecom
                                                          April 14, 2008


 A Backward Recursive PCE-based Computation (BRPC) Procedure To Compute
  Shortest Constrained Inter-domain Traffic Engineering Label Switched
                                 Paths

                       draft-ietf-pce-brpc-09.txt

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Abstract

   The ability to compute shortest constrained Traffic Engineering Label
   Switched Paths (TE LSPs) in Multiprotocol Label Switching (MPLS) and
   Generalized MPLS (GMPLS) networks across multiple domains (where a
   domain is a collection of network elements within a common sphere of
   address management or path computational responsibility such as an



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   IGP area or an Autonomous Systems) has been identified as a key
   requirement.  This document specifies a procedure relying on the use
   of multiple Path Computation Elements (PCEs) to compute such inter-
   domain shortest constrained paths across a predetermined sequence of
   domains, using a backward recursive path computation technique.  This
   technique preserves confidentiality across domains, which is
   sometimes required when domains are managed by different Service
   Providers.

Requirements Language

   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 RFC 2119 [RFC2119].





































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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  General Assumptions  . . . . . . . . . . . . . . . . . . . . .  5
   4.  BRPC Procedure . . . . . . . . . . . . . . . . . . . . . . . .  6
     4.1.  Domain Path Selection  . . . . . . . . . . . . . . . . . .  7
     4.2.  Mode of Operation  . . . . . . . . . . . . . . . . . . . .  7
   5.  PCEP Protocol Extensions . . . . . . . . . . . . . . . . . . .  9
   6.  VSPT Encoding  . . . . . . . . . . . . . . . . . . . . . . . . 10
   7.  Inter-AS TE Links  . . . . . . . . . . . . . . . . . . . . . . 10
   8.  Usage In Conjunction With Per-domain Path Computation  . . . . 11
   9.  BRPC Procedure Completion Failure  . . . . . . . . . . . . . . 11
   10. Applicability  . . . . . . . . . . . . . . . . . . . . . . . . 12
     10.1. Diverse end-to-end path computation  . . . . . . . . . . . 12
     10.2. Path Optimality  . . . . . . . . . . . . . . . . . . . . . 12
   11. Reoptimization Of An Inter-domain TE LSP . . . . . . . . . . . 13
   12. Path Computation Failure . . . . . . . . . . . . . . . . . . . 13
   13. Metric Normalization . . . . . . . . . . . . . . . . . . . . . 13
   14. Manageability Considerations . . . . . . . . . . . . . . . . . 14
     14.1. Control of Function And Policy . . . . . . . . . . . . . . 14
     14.2. Information And Data Models  . . . . . . . . . . . . . . . 14
     14.3. Liveness Detection and Monitoring  . . . . . . . . . . . . 14
     14.4. Verifying Correct Operation  . . . . . . . . . . . . . . . 14
     14.5. Requirements on Other Protocols and Functional
           Components . . . . . . . . . . . . . . . . . . . . . . . . 15
     14.6. Impact on Network Operation  . . . . . . . . . . . . . . . 15
     14.7. Path Computation Chain Monitoring  . . . . . . . . . . . . 15
   15. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 15
     15.1. New Flag Of The RP Object  . . . . . . . . . . . . . . . . 15
     15.2. New Error-Type And Error-Value . . . . . . . . . . . . . . 15
     15.3. New Flag Of The NO-PATH-VECTOR TLV . . . . . . . . . . . . 16
   16. Security Considerations  . . . . . . . . . . . . . . . . . . . 16
   17. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 16
   18. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
     18.1. Normative References . . . . . . . . . . . . . . . . . . . 16
     18.2. Informative References . . . . . . . . . . . . . . . . . . 17
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 18
   Intellectual Property and Copyright Statements . . . . . . . . . . 20












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1.  Introduction

   The requirements for inter-area and inter-AS MPLS Traffic Engineering
   (TE) have been developed by the Traffic Engineering Working Group (TE
   WG) and have been stated in [RFC4105] and [RFC4216], respectively.

   The framework for inter-domain Multiprotocol Label Switching (MPLS)
   Traffic Engineering (TE) has been provided in [RFC4726].

   [RFC5152] defines a technique for establishing an inter-domain
   Generalized MPLS (GMPLS) TE Label Switched Path (LSP) whereby the
   path is computed during the signalling process on a per-domain basis
   by the entry boundary node of each domain (each node responsible for
   triggering the computation of a section of an inter-domain TE LSP
   path is always along the path of such TE LSP).  This path computation
   technique fulfills some of the requirements stated in [RFC4105] and
   [RFC4216] but not all of them.  In particular, it cannot guarantee to
   find an optimal (shortest) inter-domain constrained path.
   Furthermore, it cannot be efficiently used to compute a set of inter-
   domain diversely routed TE LSPs.

   The Path Computation Element (PCE) architecture is defined in
   [RFC4655].  The aim of this document is to describe a PCE-based path
   computation procedure to compute optimal inter-domain constrained
   (G)MPLS TE LSPs.

   Qualifying a path as optimal requires some clarification.  Indeed, a
   globally optimal TE LSP placement usually refers to a set of TE LSPs
   whose placements optimize the network resources with regards to a
   specified objective function (e.g., a placement that reduces the
   maximum or average network load while satisfying the TE LSP
   constraints).  In this document, an optimal inter-domain constrained
   TE LSP is defined as the shortest path satisfying the set of required
   constraints that would be obtained in the absence of multiple domains
   (in other words, in a totally flat IGP network between the source and
   destination of the TE LSP).  Note that this requires to use
   consistent metric schemes in each domain (see section Section 13).


2.  Terminology

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

   ASBR: Autonomous System Border Routers.  Routers used to connect
   together ASes of the same or different Service Providers via one or
   more Inter-AS links.




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   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
   a determined sequence of domains.

   Exit BN of domain(n): a BN connecting domain(n) to domain(n+1) along
   a determined sequence of domains.

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

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

   LSR: Label Switching Router.

   LSP: Label Switched Path.

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

   TED: Traffic Engineering Database.

   VSPT: Virtual Shortest Path Tree.

   The notion of contiguous, stitched and nested TE LSPs is defined in
   [RFC4726] and will not be repeated here.


3.  General Assumptions

   In the rest of this document, we make the following set of
   assumptions common to inter-area and inter-AS MPLS TE:

   o  Each IGP area or Autonomous System (AS) is assumed to be Traffic
      Engineering enabled.

   o  No topology or resource information is distributed between domains
      (as mandated per [RFC4105] and [RFC4216]), which is critical to
      preserve IGP/BGP scalability and confidentiality.





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   o  While certain constraints like bandwidth can be used across
      different domains, other TE constraints like resource affinity,
      color, metric, etc. as listed in [RFC2702] could be translated at
      domain boundaries.  If required, it is assumed that, at the domain
      boundary nodes, there will exist some sort of local mapping based
      on policy agreement, in order to translate such constraints across
      domain boundaries during the inter-PCE communication process.

   o  Each AS can be made of several IGP areas.  The path computation
      procedure described in this document applies to the case of a
      single AS made of multiple IGP areas, multiple ASes made of a
      single IGP area or any combination of the above.  For the sake of
      simplicity, each AS will be considered to be made of a single area
      in this document.  The case of an Inter-AS TE LSP spanning
      multiple ASes where some of those ASes are themselves made of
      multiple IGP areas can be easily derived from this case by
      applying the BRPC procedure described in this document,
      recursively.

   o  The domain path (set of domains traversed to reach the destination
      domain) is either administratively pre-determined or discovered by
      some means that is outside of the scope of this document.


4.  BRPC Procedure

   The BRPC procedure is a Multiple-PCE path computation technique as
   described in [RFC4655].  A possible model consists of hosting the PCE
   function on boundary nodes (e.g., ABR or ASBR) but this is not
   mandated by the BRPC procedure.

   The BRPC procedure relies on communication between cooperating PCEs.
   In particular, the PCC sends a PCReq to a PCE in its domain.  The
   request is forwarded between PCEs, domain-by-domain until the PCE
   responsible for the domain containing the LSP destination is reached.
   The PCE in the destination domain creates a tree of potential paths
   to the destination (the Virtual Shortest Path Tree - VSPT) and passes
   this back to the previous PCE in a PCRep.  Each PCE in turn adds to
   the VSPT and passes it back until the PCE in the source domain uses
   the VSPT to select an end-to-end path that it sends to the PCC.

   The BRPC procedure does not make any assumption with regards to the
   nature of the inter-domain TE LSP that could be contiguous, nested or
   stitched.

   Furthermore, no assumption is made on the actual path computation
   algorithm in use by a PCE (e.g., it can be any variant of CSPF or an
   algorithm based on linear-programming to solve multi-constraint



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   optimization problems).

4.1.  Domain Path Selection

   The PCE-based BRPC procedure applies to the computation of an optimal
   constrained inter-domain TE LSP.  The sequence of domains to be
   traversed is either administratively pre-determined or discovered by
   some means that is outside of the scope of this document.  The PCC
   MAY indicate the sequence of domains to be traversed using the IRO
   defined in [I-D.ietf-pce-pcep] so that it is available to all PCEs.
   Note also that a sequence of PCEs MAY be enforced by policy on the
   PCC and this constraint can be carried in the PCEP path computation
   request (as defined in [I-D.ietf-pce-monitoring]).

   The BRPC procedure guarantees to compute the optimal path across a
   specific sequence of traversed domains (which constitutes an
   additional constraint).  In the case of an arbitrary set of meshed
   domains, the BRPC procedure can be used to compute the optimal path
   across each domain set in order to get the optimal constrained path
   between the source and the destination of the TE LSP.  The BRPC
   procedure can also be used across a subset of all domain sequences,
   and the best path among these sequences can then be selected.

4.2.  Mode of Operation

   Definition of VSPT(i)

   In each domain i:

   o  There is a set of X-en(i) entry BNs noted BN-en(k,i) where BN-
      en(k,i) is the kth entry BN of domain(i).

   o  There is a set of X-ex(i) exit BNs noted BN-ex(k,i) where BN-
      ex(k,i) is the kth exit BN of domain(i).

   VSPT(i): MP2P (MultiPoint To Point) tree returned by PCE(i) to
   PCE(i-1):


               Root (TE LSP destination)
               /         I            \
         BN-en(1,i)   BN-en(2,i) ... BN-en(j,i).

   Where [X-en(i)] is the number of entry BNs in domain i
   and j<= [X-en(i)]

                 Figure 1 - MP2P Tree




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   Each link of tree VSPT(i) represents the shortest constrained path
   between BN-en(j,i) and the TE LSP destination that satisfies the set
   of required constraints for the TE LSP (bandwidth, affinities, ...).
   These are path segments to reach the TE LSP destination from BN-
   en(j,i).

   Note that PCE(i) only considers the entry BNs of domain(i).  That is
   only the BNs that provide connectivity from domain(i-1).  That is,
   the set BN-en(k,i) is only made of those BNs that provide
   connectivity from domain (i-1) to domain(i).  Furthermore, some BNs
   may be excluded according to policy constraints (either due to local
   policy or policies signaled in the path computation request).

   Step 1: the PCC needs to first determine the PCE capable of serving
   its path computation request (this can be done thanks to local
   configuration or via IGP discovery (see [RFC5088] and [RFC5089])).
   The path computation request is then relayed until reaching a PCE(n)
   such that the TE LSP destination resides in the domain(n).  At each
   step of the process, the next PCE can either be statically configured
   or dynamically discovered via IGP/BGP extensions.  If no next PCE can
   be found or the next hop PCE of choice is unavailable, the procedure
   stops and a path computation error is returned (see Section 9).  If
   PCE(i-1) discovers multiple PCEs for the adjacent domain(i), PCE(i)
   may select a subset of these PCEs based on some local policies or
   heuristics.  The PCE selection process is outside of the scope of
   this document.

   Step 2: PCE(n) computes VSPT(n) made of the list of shortest
   constrained paths between every BN-en(j,n) and the TE LSP destination
   using a suitable path computation algorithm (e.g.  CSPF) and returns
   the computed VSPT(n) to PCE(n-1).

   Step i:

   - For i=n-1 to 2: PCE(i) computes VSPT(i), the tree made of the
   shortest constrained paths between each BN-en(j,i) and the TE LSP
   destination.  It does this by considering its own TED and the
   information in VSPT(i+1).

   In the case of Inter-AS TE LSP computation, this requires to also add
   the inter-AS TE links connecting the domain(i) to the domain(i+1).

   Step n

   Finally PCE(1) computes the end-to-end shortest constrained path from
   the source to the destination and returns the corresponding path to
   the requesting PCC in the form of a PCRep message as defined in
   [I-D.ietf-pce-pcep].



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   Each branch of the VSPT tree (path) may be returned in the form of an
   explicit path (in which case all the hops along the path segment are
   listed) or a loose path (in which case only the BN is specified) so
   as to preserve confidentiality along with the respective cost.  In
   the later case, various techniques can be used in order to retrieve
   the computed explicit paths on a per domain basis during the
   signaling process thanks to the use of path keys as described in
   [I-D.ietf-pce-path-key].

   A PCE that can compute the requested path for more than one
   consecutive domain on the path SHOULD perform this computation for
   all such domains before passing the PCRep to the previous PCE in the
   sequence.

   BRPC guarantees to find the optimal (shortest) constrained inter-
   domain TE LSP according to a set of defined domains to be traversed.
   Note that other variants of the BRPC procedure relying on the same
   principles are also possible.

   Note also that in case of ECMP paths, more than one path could be
   returned to the requesting LSR.


5.  PCEP Protocol Extensions

   The BRPC procedure requires the specification of a new flag of the RP
   object carried within the PCReq message (defined in
   [I-D.ietf-pce-pcep]) to specify that the shortest paths satisfying
   the constraints from the destination to the set of entry boundary
   nodes are requested (such set of paths forms the downstream VSPT as
   specified in Section 4.2).

   The following new flag of the RP object is defined:

   VSPT Flag
   Bit Number      Name Flag
     7                VSPT

   When set, the VSPT Flag indicates that the PCC requests the
   computation of an inter-domain TE LSP using the BRPC procedure
   defined in this document.

   Because path segments computed by a downstream PCE in the context of
   the BRPC procedure MUST be provided along with their respective path
   costs, the C flag of the METRIC object carried within the PCReq
   message MUST be set.  It is the choice of the requester to
   appropriately set the O bit of the RP object.




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6.  VSPT Encoding

   The VSPT is returned within a PCRep message.  The encoding consists
   of a non-ordered lists of EROs where each ERO represents a path
   segment from a BN to the destination specified in the END-POINT
   object of the corresponding PCReq message.

   Example:


   <---- area 1 ----><---- area 0 -----><------ area 2 ------>
                                       ABR1-A-B-+
                                        |       |
                                       ABR2-----D
                                        |       |
                                       ABR3--C--+

    Figure 2 - An Example of VPST Encoding Using a Set of EROs

   In the simple example shown in figure 2, if we make the assumption
   that a constrained path exists between each ABR and the destination
   D, the VSPT computed by a PCE serving area 2 consists of the
   following non-ordered set of EROs:

   o  ERO1: ABR1(TE Router ID)-A(Interface IP address)-B(Interface IP
      address)-D(TE Router ID)

   o  ERO2: ABR2(TE Router ID)-D(TE Router ID)

   o  ERO3: ABR3(TE Router ID)-C(interface IP adress)-D(TE Router ID)

   The PCReq message, PCRep message, PCEP END-POINT and ERO objects are
   defined in [I-D.ietf-pce-pcep]


7.  Inter-AS TE Links

   In the case of Inter-AS TE LSP path computation, the BRPC procedure
   requires the knowledge of the traffic engineering attributes of the
   Inter-AS TE links: the process by which the PCE acquires this
   information is out of the scope of the BRPC procedure, which is
   compliant with the PCE architecture defined in [RFC4655].

   That said, a straightforward solution consists of allowing the ASBRs
   to flood the TE information related to the inter-ASBR links although
   no IGP TE is enabled over those links (there is no IGP adjacency over
   the inter-ASBR links).  This allows the PCE of a domain to get entire
   TE visibility up to the set of entry ASBRs in the downstream domain



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   (see the IGP extensions defined in
   [I-D.ietf-ccamp-isis-interas-te-extension] and
   [I-D.ietf-ccamp-ospf-interas-te-extension]).


8.  Usage In Conjunction With Per-domain Path Computation

   The BRPC procedure may be used to compute path segments in
   conjunction with other path computation techniques (such as the per-
   domain path computation technique defined in [RFC5152]) to compute
   the end-to-end path.  In this case end-to-end path optimality can no
   longer be guaranteed.


9.  BRPC Procedure Completion Failure

   If the BRPC procedure cannot be completed because a PCE along the
   domain does not recognize the procedure (VSPT flag of the RP object),
   as stated in [I-D.ietf-pce-pcep], the PCE sends a PCErr message to
   the upstream PCE with an Error-Type=4 (not supported object), Error-
   value-4 (Unsupported paramater).  The PCE may include the parent
   object (RP object) up to and including (but no further than) the
   unknown or unsupported parameter.  In this case where the unknown or
   unsupported parameter is a bit flag (VSPT flag), the included RP
   object should contain the whole bit flag field with all bits after
   the parameter at issue set to zero.  The corresponding path
   computation request is then cancelled by the PCE without further
   notification.

   If the BRPC procedure cannot be completed because a PCE along the
   domain path recognises but does not support the procedure, it MUST
   return a PCErr message to the upstream PCE with an Error-Type "BRPC
   procedure completion failure".

   The PCErr message MUST be relayed to the requesting PCC.

   PCEP-ERROR objects are used to report a PCEP protocol error and are
   characterized by an Error-Type which specifies the type of error and
   an Error-value that provides additional information about the error
   type.  Both the Error-Type and the Error-Value are managed by IANA.
   A new Error-Type is defined that relates to the BRPC procedure.










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  Error-type       Meaning
      13           BRPC procedure completion failure
                   Error-value
                     1: BRPC procedure not supported by one or more PCEs
                        along the domain path


10.  Applicability

   As discussed in Section 3, the requirements for inter-area and
   inter-AS MPLS Traffic Engineering have been developed by the Traffic
   Engineering Working Group (TE WG) and have been stated in [RFC4105]
   and [RFC4216], respectively.  Among the set of requirements, both
   documents indicate the need for some solution providing the ability
   to compute an optimal (shortest) constrained inter-domain TE LSP and
   to compute a set of diverse inter-domain TE LSPs.

10.1.  Diverse end-to-end path computation

   PCEP (see [I-D.ietf-pce-pcep]) allows a PCC to request the
   computation of a set of diverse TE LSPs thanks to the SVEC object by
   setting the flags L, N or S to request link, node or SRLG diversity
   respectively.  Such requests MUST be taken into account by each PCE
   along the path computation chain during the VSPT computation.  In the
   context of the BRPC procedure, a set of diversely routed TE LSPs
   between two LSRs can be computed since the paths segments of the VSPT
   are simultaneously computed by a given PCE.  The BRPC procedure
   allows for the computation of diverse paths under various objective
   functions (such as minimizing the sum of the costs of the N diverse
   paths, etc).

   By constrast, with a 2-step approach consisting of computing the
   first path followed by the computation of the second path after
   having removed the set of network elements traversed by the first
   path (if that does not violate confidentiality preservation), one
   cannot guarantee that a solution will be found even if such solution
   exists.  Furthermore, even if a solution is found, it may not be the
   most optimal one with respect to an objective function such as
   minimizing the sum of the paths costs, bounding the path delays of
   both paths and so on.  Finally, it must be noted that such a 2-step
   path computation approach is usually less efficient in term of
   signalling delays since it requires two serialized TE LSP set up.

10.2.  Path Optimality

   BRPC guarantees that the optimal (shortest) constrained inter-domain
   path will always be found subject to policy constraints.  When
   combined with other local path computation techniques (e.g. in the



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   case of stitched/nested TE LSP) and in the case where a domain has
   more than one BN-en or more than one BN-ex, optimality after some
   network change within the domain can only be guaranteed by re-
   executing the BRPC procedure.


11.  Reoptimization Of An Inter-domain TE LSP

   The ability to reoptimize an existing inter-domain TE LSP path has
   been explicitly listed as a requirement in [RFC4105] and [RFC4216].
   In the case of a TE LSP reoptimization request, the reoptimization
   procedure defined in [I-D.ietf-pce-pcep] applies where the path in
   use (if available on the head-end) is provided as part of the path
   computation request in order for the PCEs involved in the
   reoptimization request to avoid double bandwidth accounting.


12.  Path Computation Failure

   If a PCE requires to relay a path computation request according to
   the BRPC procedure defined in this document to a downstream PCE and
   no such PCE is available, the PCE MUST send a negative path
   computation reply to the requester using a PCReq message as specified
   in [I-D.ietf-pce-pcep] that contains a NO-PATH object.  In such case,
   the NO-PATH object MUST carry a NO-PATH-VECTOR TLV (defined in
   [I-D.ietf-pce-pcep]) with the newly defined bit named "BRPC Path
   Computation chain unavailable" set.

   Bit number     Name Flag
      4           BRPC Path computation chain unavailable


13.  Metric Normalization

   In the case of inter-area TE, the same IGP/TE metric scheme is
   usually adopted for all the IGP areas (e.g., based on the link-speed,
   propagation delay or some other combination of link attributes).
   Hence, the proposed set of mechanisms always computes the shortest
   path across multiple areas obeying the required set of constraints
   with respect to a specified objective function.  Conversely, in the
   case of Inter-AS TE, in order for this path computation to be
   meaningful, metric normalization between ASes may be required.  One
   solution to avoid IGP metric modification would be for the Service
   Providers to agree on a TE metric normalization scheme and use the TE
   metric for TE LSP path computation (in that case, this must be
   requested in the PCEP Path computation request) using the METRIC
   object (defined in [I-D.ietf-pce-pcep]).




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14.  Manageability Considerations

   This section follows the guidance of
   [I-D.ietf-pce-manageability-requirements].

14.1.  Control of Function And Policy

   The only configurable item is the support of the BRPC procedure on a
   PCE.  The support of the BRPC procedure by the PCE MAY be controlled
   by a policy module governing the conditions under which a PCE should
   participate to the BRPC procedure (origin of the requests, number of
   requests per second, ...).  If the BRPC is not supported/allowed on a
   PCE, it MUST send a PCErr message as specified in Section 9.

14.2.  Information And Data Models

   A BRPC MIB module will be specified in a separate document.

14.3.  Liveness Detection and Monitoring

   The BRPC procedure is a Multiple-PCE path computation technique and
   as such a set of PCEs are involved in the path computation chain.  If
   the path computation chain is not operational either because at least
   one PCE does not support the BRPC procedure or because one of the
   PCEs that must be involved in the path computation chain is not
   available, procedures are defined to report such failures in
   Section 9 and Section 12 respectively.  Furthermore, a built-in
   diagnostic tool to check the availability and performances of a PCE
   chain is defined in [I-D.ietf-pce-monitoring].

14.4.  Verifying Correct Operation

   Verifying the correct operation of BRPC can be performed by
   monitoring a set of parameters.  A BRPC implementation SHOULD provide
   the following parameters:

   o Number of successful BRPC Procedure completions on a per PCE peer
   basis,

   o Number of BRPC procedure completion failures because the VSPT flag
   was not recognized (on a per PCE peer basis),

   o Number of BRPC procedure completetion failures because the BRPC
   procedure was not supported (on a per PCE peer basis),







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14.5.  Requirements on Other Protocols and Functional Components

   The BRPC procedure does not put any new requirements on other
   protocol.  That said, since the BRPC procedure relies on the PCEP
   protocol, there is a dependency between BRPC and PCEP; consequently
   the BRPC procedure inherently makes use of the management functions
   developed for PCEP.

14.6.  Impact on Network Operation

   The BRPC procedure does not have any significant impact on network
   operation: indeed, BRPC is a Multiple-PCE path computation scheme as
   defined in [RFC4655] and does not differ from any other path
   computation request.

14.7.  Path Computation Chain Monitoring

   [I-D.ietf-pce-monitoring] specifies a set of mechanisms that can be
   used to gather PCE state metrics.  Because BRPC is a Multiple-PCE
   path computation techniques, such mechanism could be advantageously
   used in the context of the BRPC procedure to check the liveness of
   the path computation chain, locate a faulty component, monitor the
   overall performance and so on.


15.  IANA Considerations

15.1.  New Flag Of The RP Object

   A new flag of the RP object (specified in [I-D.ietf-pce-pcep]) is
   defined in this document.

   VSPT Flag
   Bit Number      Name Flag    Reference
     7                VSPT      This document

15.2.  New Error-Type And Error-Value

   A new Error-Type is defined in this document (Error-Type and Error-
   value to be assigned by IANA).











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    Error-type       Meaning                             Reference
        13           BRPC procedure completion failure   This document
                     Error-value
                      1: BRPC procedure not supported by
                         one a PCE along the domain path

15.3.  New Flag Of The NO-PATH-VECTOR TLV

   A new flag of the NO-PATH-VECTOR TLV defined in [I-D.ietf-pce-pcep])
   is specified in this document.

    Bit number  Meaning                  Reference

       4        BRPC Path computation   This document
                chain unavailable


16.  Security Considerations

   The BRPC procedure relies on the use of the PCEP protocol and as such
   is subjected to the potential attacks listed in section 11 of
   [I-D.ietf-pce-pcep].  In addition to the security mechanisms
   described in [I-D.ietf-pce-pcep] with regards to spoofing, snooping,
   falsification and Denial of Service, an implementation MAY support a
   policy module governing the conditions under which a PCE should
   participate to the BRPC procedure.

   The BRPC procedure does not increase the information exchanged
   between ASes and preserves topology confidentiality, in compliance
   with [RFC4105] and [RFC4216].


17.  Acknowledgements

   The authors would like to thank Arthi Ayyangar, Dimitri
   Papadimitriou, Siva Sivabalan, Meral Shirazipour and Mach Chen for
   their useful comments.  A special thank to Adrian Farrel for his
   useful comments and suggestions.


18.  References

18.1.  Normative References

   [I-D.ietf-pce-pcep]
              Ayyangar, A., Oki, E., Atlas, A., Dolganow, A., Ikejiri,
              Y., Kumaki, K., Vasseur, J., and J. Roux, "Path
              Computation Element (PCE) Communication Protocol (PCEP)",



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              draft-ietf-pce-pcep-12 (work in progress), March 2008.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

18.2.  Informative References

   [I-D.ietf-ccamp-isis-interas-te-extension]
              Chen, M., Zhang, R., and X. Duan, "ISIS Extensions in
              Support of Inter-AS Multiprotocol Label Switching (MPLS)
              and Generalized MPLS (GMPLS) Traffic Engineering",
              draft-ietf-ccamp-isis-interas-te-extension-02 (work in
              progress), April 2008.

   [I-D.ietf-ccamp-ospf-interas-te-extension]
              Chen, M., Zhang, R., and X. Duan, "OSPF Extensions in
              Support of Inter-AS Multiprotocol Label Switching (MPLS)
              and Generalized MPLS (GMPLS) Traffic Engineering",
              draft-ietf-ccamp-ospf-interas-te-extension-05 (work in
              progress), April 2008.

   [I-D.ietf-pce-manageability-requirements]
              Farrel, A., "Inclusion of Manageability Sections in PCE
              Working Group Drafts",
              draft-ietf-pce-manageability-requirements-03 (work in
              progress), February 2008.

   [I-D.ietf-pce-monitoring]
              Vasseur, J., Roux, J., and Y. Ikejiri, "A set of
              monitoring tools for Path Computation Element based
              Architecture", draft-ietf-pce-monitoring-01 (work in
              progress), February 2008.

   [I-D.ietf-pce-path-key]
              Bradford, R. and J. Vasseur, "Preserving Topology
              Confidentiality in Inter-Domain Path Computation Using a
              Key-Based Mechanism", draft-ietf-pce-path-key-02 (work in
              progress), February 2008.

   [RFC2702]  Awduche, D., Malcolm, J., Agogbua, J., O'Dell, M., and J.
              McManus, "Requirements for Traffic Engineering Over MPLS",
              RFC 2702, September 1999.

   [RFC4105]  Le Roux, J., Vasseur, J., and J. Boyle, "Requirements for
              Inter-Area MPLS Traffic Engineering", RFC 4105, June 2005.

   [RFC4216]  Zhang, R. and J. Vasseur, "MPLS Inter-Autonomous System
              (AS) Traffic Engineering (TE) Requirements", RFC 4216,



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              November 2005.

   [RFC4655]  Farrel, A., Vasseur, J., and J. Ash, "A Path Computation
              Element (PCE)-Based Architecture", RFC 4655, August 2006.

   [RFC4726]  Farrel, A., Vasseur, J., and A. Ayyangar, "A Framework for
              Inter-Domain Multiprotocol Label Switching Traffic
              Engineering", RFC 4726, November 2006.

   [RFC5088]  Le Roux, JL., Vasseur, JP., Ikejiri, Y., and R. Zhang,
              "OSPF Protocol Extensions for Path Computation Element
              (PCE) Discovery", RFC 5088, January 2008.

   [RFC5089]  Le Roux, JL., Vasseur, JP., Ikejiri, Y., and R. Zhang,
              "IS-IS Protocol Extensions for Path Computation Element
              (PCE) Discovery", RFC 5089, January 2008.

   [RFC5152]  Vasseur, JP., Ayyangar, A., and R. Zhang, "A Per-Domain
              Path Computation Method for Establishing Inter-Domain
              Traffic Engineering (TE) Label Switched Paths (LSPs)",
              RFC 5152, February 2008.


Authors' Addresses

   JP Vasseur (editor)
   Cisco Systems, Inc
   1414 Massachusetts Avenue
   Boxborough, MA  01719
   USA

   Email: jpv@cisco.com


   Raymond Zhang
   BT Infonet
   2160 E. Grand Ave.
   El Segundo, CA  90025
   USA

   Email: raymond_zhang@bt.infonet.com










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   Nabil Bitar
   Verizon
   40 Sylvan Road
   Waltham, MA  02145
   USA

   Email: nabil.bitar@verizon.com


   JL Le Roux
   France Telecom
   2, Avenue Pierre-Marzin
   Lannion,   22307
   FRANCE

   Email: jeanlouis.leroux@orange-ft.com



































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