






Network Working Group                                   JL. Le Roux, Ed.
Request for Comments: 5088                                France Telecom
Category: Standards Track                               JP. Vasseur, Ed.
                                                       Cisco System Inc.
                                                              Y. Ikejiri
                                                      NTT Communications
                                                                R. Zhang
                                                                      BT
                                                            January 2008


 OSPF Protocol Extensions for Path Computation Element (PCE) Discovery

Status of This Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Abstract

   There are various circumstances where it is highly desirable for a
   Path Computation Client (PCC) to be able to dynamically and
   automatically discover a set of Path Computation Elements (PCEs),
   along with information that can be used by the PCC for PCE selection.
   When the PCE is a Label Switching Router (LSR) participating in the
   Interior Gateway Protocol (IGP), or even a server participating
   passively in the IGP, a simple and efficient way to announce PCEs
   consists of using IGP flooding.  For that purpose, this document
   defines extensions to the Open Shortest Path First (OSPF) routing
   protocol for the advertisement of PCE Discovery information within an
   OSPF area or within the entire OSPF routing domain.
















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Table of Contents

   1. Introduction ....................................................2
   2. Terminology .....................................................4
   3. Overview ........................................................5
      3.1. PCE Discovery Information ..................................5
      3.2. Flooding Scope .............................................5
   4. The OSPF PCED TLV ...............................................6
      4.1. PCE-ADDRESS Sub-TLV ........................................7
      4.2. PATH-SCOPE Sub-TLV .........................................8
      4.3. PCE-DOMAIN Sub-TLV ........................................10
      4.4. NEIG-PCE-DOMAIN Sub-TLV ...................................11
      4.5. PCE-CAP-FLAGS Sub-TLV .....................................12
   5. Elements of Procedure ..........................................13
   6. Backward Compatibility .........................................14
   7. IANA Considerations ............................................14
      7.1. OSPF TLV ..................................................14
      7.2. PCE Capability Flags Registry .............................14
   8. Security Considerations ........................................15
   9. Manageability Considerations ...................................16
      9.1. Control of Policy and Functions ...........................16
      9.2. Information and Data Model ................................16
      9.3. Liveness Detection and Monitoring .........................16
      9.4. Verify Correct Operations .................................16
      9.5. Requirements on Other Protocols and Functional
           Components ................................................16
      9.6. Impact on Network Operations ..............................17
   10. Acknowledgments ...............................................17
   11. References ....................................................17
      11.1. Normative References .....................................17
      11.2. Informative References ...................................18

1.  Introduction

   [RFC4655] describes the motivations and architecture for a Path
   Computation Element (PCE)-based path computation model for
   Multi-Protocol Label Switching (MPLS) and Generalized MPLS (GMPLS)
   Traffic Engineered Label Switched Paths (TE LSPs).  The model allows
   for the separation of the PCE from a Path Computation Client (PCC)
   (also referred to as a non co-located PCE) and allows for cooperation
   between PCEs (where one PCE acts as a PCC to make requests of the
   other PCE).  This relies on a communication protocol between a PCC
   and PCE, and also between PCEs.  The requirements for such a
   communication protocol can be found in [RFC4657], and the
   communication protocol is defined in [PCEP].






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   The PCE architecture requires that a PCC be aware of the location of
   one or more PCEs in its domain, and, potentially, of PCEs in other
   domains, e.g., in the case of inter-domain TE LSP computation.

   A network may contain a large number of PCEs, each with potentially
   distinct capabilities.  In such a context, it is highly desirable to
   have a mechanism for automatic and dynamic PCE discovery that allows
   PCCs to automatically discover a set of PCEs, along with additional
   information about each PCE that may be used by a PCC to perform PCE
   selection.  Additionally, it is valuable for a PCC to dynamically
   detect new PCEs, failed PCEs, or any modification to the PCE
   information.  Detailed requirements for such a PCE discovery
   mechanism are provided in [RFC4674].

   Note that the PCE selection algorithm applied by a PCC is out of the
   scope of this document.

   When PCCs are LSRs participating in the IGP (OSPF or IS-IS), and PCEs
   are either LSRs or servers also participating in the IGP, an
   effective mechanism for PCE discovery within an IGP routing domain
   consists of utilizing IGP advertisements.

   This document defines extensions to OSPFv2 [RFC2328] and OSPFv3
   [RFC2740] to allow a PCE in an OSPF routing domain to advertise its
   location, along with some information useful to a PCC for PCE
   selection, so as to satisfy dynamic PCE discovery requirements set
   forth in [RFC4674].

   Generic capability advertisement mechanisms for OSPF are defined in
   [RFC4970].  These allow a router to advertise its capabilities within
   an OSPF area or an entire OSPF routing domain.  This document
   leverages this generic capability advertisement mechanism to fully
   satisfy the dynamic PCE discovery requirements.

   This document defines a new TLV (named the PCE Discovery TLV (PCED
   TLV)) to be carried within the OSPF Router Information LSA
   ([RFC4970]).

   The PCE information advertised is detailed in Section 3.  Protocol
   extensions and procedures are defined in Sections 4 and 5.

   The OSPF extensions defined in this document allow for PCE discovery
   within an OSPF routing domain.  Solutions for PCE discovery across
   Autonomous System boundaries are beyond the scope of this document,
   and are for further study.






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2.  Terminology

   ABR: OSPF Area Border Router.

   AS: Autonomous System.

   IGP: Interior Gateway Protocol.  Either of the two routing protocols,
   Open Shortest Path First (OSPF) or Intermediate System to
   Intermediate System (IS-IS).

   Intra-area TE LSP: A TE LSP whose path does not cross an IGP area
   boundary.

   Intra-AS TE LSP: A TE LSP whose path does not cross an AS boundary.

   Inter-area TE LSP: A TE LSP whose path transits two or more IGP
   areas.  That is, a TE LSP that crosses at least one IGP area
   boundary.

   Inter-AS TE LSP: A TE LSP whose path transits two or more ASes or
   sub-ASes (BGP confederations).  That is, a TE LSP that crosses at
   least one AS boundary.

   LSA: Link State Advertisement.

   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.

   PCED: PCE Discovery.

   PCE-Domain: In a PCE context, this refers to any collection of
   network elements within a common sphere of address management or path
   computational responsibility (referred to as a "domain" in
   [RFC4655]).  Examples of PCE-Domains include IGP areas and ASes.
   This should be distinguished from an OSPF routing domain.

   PCEP: Path Computation Element communication Protocol.

   TE LSP: Traffic Engineered Label Switched Path.

   TLV: Type-Length-Variable data encoding.




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   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].

   IS-IS extensions for PCE discovery are defined in [RFC5089].

3.  Overview

3.1.  PCE Discovery Information

   The PCE discovery information is composed of:

   -  The PCE location: an IPv4 and/or IPv6 address that is used to
      reach the PCE.  It is RECOMMENDED to use an address that is always
      reachable if there is any connectivity to the PCE;

   -  The PCE path computation scope (i.e., intra-area, inter-area,
      inter-AS, or inter-layer);

   -  The set of one or more PCE-Domain(s) into which the PCE has
      visibility and for which the PCE can compute paths;

   -  The set of zero, one, or more neighbor PCE-Domain(s) toward which
      the PCE can compute paths;

   -  A set of communication capabilities (e.g., support for request
      prioritization) and path computation-specific capabilities (e.g.,
      supported constraints).

   PCE discovery information is, by nature, fairly static and does not
   change with PCE activity.  Changes in PCE discovery information may
   occur as a result of PCE configuration updates, PCE
   deployment/activation, PCE deactivation/suppression, or PCE failure.
   Hence, this information is not expected to change frequently.

3.2.  Flooding Scope

   The flooding scope for PCE information advertised through OSPF can be
   limited to one or more OSPF areas the PCE belongs to, or can be
   extended across the entire OSPF routing domain.

   Note that some PCEs may belong to multiple areas, in which case the
   flooding scope may comprise these areas.  This could be the case for
   an ABR, for instance, advertising its PCE information within the
   backbone area and/or a subset of its attached IGP area(s).






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4.  The OSPF PCED TLV

   The OSPF PCE Discovery TLV (PCED TLV) contains a non-ordered set of
   sub-TLVs.

   The format of the OSPF PCED TLV and its sub-TLVs is identical to the
   TLV format used by the Traffic Engineering Extensions to OSPF
   [RFC3630].  That is, the TLV is composed of 2 octets for the type, 2
   octets specifying the TLV length, and a value field.  The Length
   field defines the length of the value portion in octets.

   The TLV is padded to 4-octet alignment; padding is not included in
   the Length field (so a 3-octet value would have a length of 3, but
   the total size of the TLV would be 8 octets).  Nested TLVs are also
   4-octet aligned.  Unrecognized types are ignored.

   The OSPF PCED TLV has the following format:

                        1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Type             |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   //                            sub-TLVs                          //
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Type:     6
      Length:   Variable
      Value:    This comprises one or more sub-TLVs

   Five sub-TLVs are defined:
         Sub-TLV type  Length               Name
               1      variable     PCE-ADDRESS sub-TLV
               2         4         PATH-SCOPE sub-TLV
               3         4         PCE-DOMAIN sub-TLV
               4         4         NEIG-PCE-DOMAIN sub-TLV
               5      variable     PCE-CAP-FLAGS sub-TLV

   The PCE-ADDRESS and PATH-SCOPE sub-TLVs MUST always be present within
   the PCED TLV.

   The PCE-DOMAIN and NEIG-PCE-DOMAIN sub-TLVs are optional.  They MAY
   be present in the PCED TLV to facilitate selection of inter-domain
   PCEs.





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   The PCE-CAP-FLAGS sub-TLV is optional and MAY be present in the PCED
   TLV to facilitate the PCE selection process.

   Malformed PCED TLVs or sub-TLVs not explicitly described in this
   document MUST cause the LSA to be treated as malformed according to
   the normal procedures of OSPF.

   Any unrecognized sub-TLV MUST be silently ignored.

   The PCED TLV is carried within an OSPF Router Information LSA defined
   in [RFC4970].

   No additional sub-TLVs will be added to the PCED TLV in the future.
   If a future application requires the advertisement of additional PCE
   information in OSPF, this will not be carried in the Router
   Information LSA.

   The following sub-sections describe the sub-TLVs that may be carried
   within the PCED TLV.

4.1.  PCE-ADDRESS Sub-TLV

   The PCE-ADDRESS sub-TLV specifies an IP address that can be used to
   reach the PCE.  It is RECOMMENDED to make use of an address that is
   always reachable, provided that the PCE is alive and reachable.

   The PCE-ADDRESS sub-TLV is mandatory; it MUST be present within the
   PCED TLV.  It MAY appear twice, when the PCE has both an IPv4 and
   IPv6 address.  It MUST NOT appear more than once for the same address
   type.  If it appears more than once for the same address type, only
   the first occurrence is processed and any others MUST be ignored.

   The format of the PCE-ADDRESS sub-TLV is as follows:

                        1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Type = 1         |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     address-type              |          Reserved             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   //                       PCE IP Address                        //
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                        PCE-ADDRESS sub-TLV format




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      Type:     1
      Length:   8 (IPv4) or 20 (IPv6)

      Address-type:
                    1   IPv4
                    2   IPv6

   Reserved: SHOULD be set to zero on transmission and MUST be ignored
   on receipt.

   PCE IP Address: The IP address to be used to reach the PCE.

4.2.  PATH-SCOPE Sub-TLV

   The PATH-SCOPE sub-TLV indicates the PCE path computation scope,
   which refers to the PCE's ability to compute or take part in the
   computation of paths for intra-area, inter-area, inter-AS, or inter-
   layer TE LSPs.

   The PATH-SCOPE sub-TLV is mandatory; it MUST be present within the
   PCED TLV.  There MUST be exactly one instance of the PATH-SCOPE
   sub-TLV within each PCED TLV.  If it appears more than once, only the
   first occurrence is processed and any others MUST be ignored.

   The PATH-SCOPE sub-TLV contains a set of bit-flags indicating the
   supported path scopes, and four fields indicating PCE preferences.

   The PATH-SCOPE sub-TLV has the following format:

                        1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Type = 2         |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |0|1|2|3|4|5|   Reserved        |PrefL|PrefR|PrefS|PrefY| Res   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Type:     2
      Length:   4
      Value:    This comprises a 2-octet flags field where each bit
                represents a supported path scope, as well as four
                preference fields used to specify PCE preferences.









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   The following bits are defined:

      Bit      Path Scope

       0      L bit:  Can compute intra-area paths.
       1      R bit:  Can act as PCE for inter-area TE LSP
                      computation.
       2      Rd bit: Can act as a default PCE for inter-area TE LSP
                      computation.
       3      S bit:  Can act as PCE for inter-AS TE LSP computation.
       4      Sd bit: Can act as a default PCE for inter-AS TE LSP
                      computation.
       5      Y bit:  Can act as PCE for inter-layer TE LSP
                      computation.

      PrefL field: PCE's preference for intra-area TE LSP computation.

      PrefR field: PCE's preference for inter-area TE LSP computation.

      PrefS field: PCE's preference for inter-AS TE LSP computation.

      PrefY field: PCE's preference for inter-layer TE LSP computation.

      Res: Reserved for future use.

   The L, R, S, and Y bits are set when the PCE can act as a PCE for
   intra-area, inter-area, inter-AS, or inter-layer TE LSP computation,
   respectively.  These bits are non-exclusive.

   When set, the Rd bit indicates that the PCE can act as a default PCE
   for inter-area TE LSP computation (that is, the PCE can compute a
   path toward any neighbor area).  Similarly, when set, the Sd bit
   indicates that the PCE can act as a default PCE for inter-AS TE LSP
   computation (the PCE can compute a path toward any neighbor AS).

   When the Rd and Sd bit are set, the PCED TLV MUST NOT contain a
   NEIG-PCE-DOMAIN sub-TLV (see Section 4.4).

   When the R bit is clear, the Rd bit SHOULD be clear on transmission
   and MUST be ignored on receipt.  When the S bit is clear, the Sd bit
   SHOULD be clear on transmission and MUST be ignored on receipt.

   The PrefL, PrefR, PrefS, and PrefY fields are each three bits long
   and allow the PCE to specify a preference for each computation scope,
   where 7 reflects the highest preference.  Such preferences can be
   used for weighted load balancing of path computation requests.  An
   operator may decide to configure a preference for each computation
   scope at each PCE so as to balance the path computation load among



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   them.  The algorithms used by a PCC to load balance its path
   computation requests according to such PCE preferences is out of the
   scope of this document and is a matter for local or network-wide
   policy.  The same or different preferences may be used for each
   scope.  For instance, an operator that wants a PCE capable of both
   inter-area and inter-AS computation to be preferred for use for
   inter-AS computations may configure PrefS higher than PrefR.

   When the L, R, S, or Y bits are cleared, the PrefL, PrefR, PrefS, and
   PrefY fields SHOULD respectively be set to 0 on transmission and MUST
   be ignored on receipt.

   Both reserved fields SHOULD be set to zero on transmission and MUST
   be ignored on receipt.

4.3.  PCE-DOMAIN Sub-TLV

   The PCE-DOMAIN sub-TLV specifies a PCE-Domain (area or AS) where the
   PCE has topology visibility and through which the PCE can compute
   paths.

   The PCE-DOMAIN sub-TLV SHOULD be present when PCE-Domains for which
   the PCE can operate cannot be inferred by other IGP information: for
   instance, when the PCE is inter-domain capable (i.e., when the R bit
   or S bit is set) and the flooding scope is the entire routing domain
   (see Section 5 for a discussion of how the flooding scope is set and
   interpreted).

   A PCED TLV may include multiple PCE-DOMAIN sub-TLVs when the PCE has
   visibility into multiple PCE-Domains.

   The PCE-DOMAIN sub-TLV has the following format:

                        1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Type = 3         |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Domain-type               |          Reserved             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Domain ID                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                        PCE-DOMAIN sub-TLV format

      Type:     3
      Length:   8




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      Two domain-type values are defined:
                    1   OSPF Area ID
                    2   AS Number

      Domain ID: With the domain-type set to 1, this indicates the
      32-bit Area ID of an area where the PCE has visibility and can
      compute paths.  With domain-type set to 2, this indicates an AS
      number of an AS where the PCE has visibility and can compute
      paths.  When the AS number is coded in two octets, the AS Number
      field MUST have its first two octets set to 0.

4.4.  NEIG-PCE-DOMAIN Sub-TLV

   The NEIG-PCE-DOMAIN sub-TLV specifies a neighbor PCE-Domain (area or
   AS) toward which a PCE can compute paths.  It means that the PCE can
   take part in the computation of inter-domain TE LSPs with paths that
   transit this neighbor PCE-Domain.

   A PCED sub-TLV may include several NEIG-PCE-DOMAIN sub-TLVs when the
   PCE can compute paths towards several neighbor PCE-Domains.

   The NEIG-PCE-DOMAIN sub-TLV has the same format as the PCE-DOMAIN
   sub-TLV:

                        1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Type = 4         |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Domain-type               |          Reserved             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Domain ID                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                        NEIG-PCE-DOMAIN sub-TLV format

      Type:     4
      Length:   8

      Two domain-type values are defined:
                    1   OSPF Area ID
                    2   AS Number

      Domain ID: With the domain-type set to 1, this indicates the
      32-bit Area ID of a neighbor area toward which the PCE can compute
      paths.  With domain-type set to 2, this indicates the AS number of





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      a neighbor AS toward which the PCE can compute paths.  When the AS
      number is coded in two octets, the AS Number field MUST have its
      first two octets set to 0.

   The NEIG-PCE-DOMAIN sub-TLV MUST be present at least once with
   domain-type set to 1 if the R bit is set and the Rd bit is cleared,
   and MUST be present at least once with domain-type set to 2 if the S
   bit is set and the Sd bit is cleared.

4.5.  PCE-CAP-FLAGS Sub-TLV

   The PCE-CAP-FLAGS sub-TLV is an optional sub-TLV used to indicate PCE
   capabilities.  It MAY be present within the PCED TLV.  It MUST NOT be
   present more than once.  If it appears more than once, only the first
   occurrence is processed and any others MUST be ignored.

   The value field of the PCE-CAP-FLAGS sub-TLV is made up of an array
   of units of 32-bit flags numbered from the most significant bit as
   bit zero, where each bit represents one PCE capability.

   The format of the PCE-CAP-FLAGS sub-TLV 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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |              Type = 5         |             Length            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
   //                 PCE Capability Flags                          //
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Type:     5
      Length:   Multiple of 4 octets
      Value:    This contains an array of units of 32-bit flags
                numbered from the most significant as bit zero, where
                each bit represents one PCE capability.














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   IANA will manage the space of the PCE Capability Flags.

   The following bits have been assigned by IANA:

      Bit       Capabilities

       0        Path computation with GMPLS link constraints
       1        Bidirectional path computation
       2        Diverse path computation
       3        Load-balanced path computation
       4        Synchronized path computation
       5        Support for multiple objective functions
       6        Support for additive path constraints
                (max hop count, etc.)
       7        Support for request prioritization
       8        Support for multiple requests per message

      9-31      Reserved for future assignments by IANA.

   These capabilities are defined in [RFC4657].

   Reserved bits SHOULD be set to zero on transmission and MUST be
   ignored on receipt.

5.  Elements of Procedure

   The PCED TLV is advertised within OSPFv2 Router Information LSAs
   (Opaque type of 4 and Opaque ID of 0) or OSPFv3 Router Information
   LSAs (function code of 12), which are defined in [RFC4970].  As such,
   elements of procedure are inherited from those defined in [RFC4970].

   In OSPFv2, the flooding scope is controlled by the opaque LSA type
   (as defined in [RFC2370]) and in OSPFv3, by the S1/S2 bits (as
   defined in [RFC2740]).  If the flooding scope is area local, then the
   PCED TLV MUST be carried within an OSPFv2 type 10 router information
   LSA or an OSPFV3 Router Information LSA with the S1 bit set and the
   S2 bit clear.  If the flooding scope is the entire IGP domain, then
   the PCED TLV MUST be carried within an OSPFv2 type 11 Router
   Information LSA or OSPFv3 Router Information LSA with the S1 bit
   clear and the S2 bit set.  When only the L bit of the PATH-SCOPE
   sub-TLV is set, the flooding scope MUST be area local.

   When the PCE function is deactivated, the OSPF speaker advertising
   this PCE MUST originate a new Router Information LSA that no longer
   includes the corresponding PCED TLV, provided there are other TLVs in
   the LSA.  If there are no other TLVs in the LSA, it MUST either send
   an empty Router Information LSA or purge it by prematurely aging it.




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   The PCE address (i.e., the address indicated within the PCE-ADDRESS
   sub-TLV) SHOULD be reachable via some prefixes advertised by OSPF.

   The PCED TLV information regarding a specific PCE is only considered
   current and useable when the router advertising this information is
   itself reachable via OSPF calculated paths in the same area of the
   LSA in which the PCED TLV appears.

   A change in the state of a PCE (activate, deactivate, parameter
   change) MUST result in a corresponding change in the PCED TLV
   information advertised by an OSPF router (inserted, removed, updated)
   in its LSA.  The way PCEs determine the information they advertise,
   and how that information is made available to OSPF, is out of the
   scope of this document.  Some information may be configured (e.g.,
   address, preferences, scope) and other information may be
   automatically determined by the PCE (e.g., areas of visibility).

   A change in information in the PCED TLV MUST NOT trigger any SPF
   computation at a receiving router.

6.  Backward Compatibility

   The PCED TLV defined in this document does not introduce any
   interoperability issues.

   A router not supporting the PCED TLV will just silently ignore the
   TLV as specified in [RFC4970].

7.  IANA Considerations

7.1.  OSPF TLV

   IANA has defined a registry for TLVs carried in the Router
   Information LSA defined in [RFC4970].  IANA has assigned a new TLV
   codepoint for the PCED TLV carried within the Router Information LSA.

   Value      TLV Name                      Reference
   -----     --------                       ----------
     6         PCED                       (this document)

7.2.  PCE Capability Flags Registry

   This document provides new capability bit flags, which are present in
   the PCE-CAP-FLAGS TLV referenced in Section 4.1.5.







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   The IANA has created a new top-level OSPF registry, the "PCE
   Capability Flags" registry, and will manage the space of PCE
   capability bit flags numbering them in the usual IETF notation
   starting at zero and continuing at least through 31, with the most
   significant bit as bit zero.

   New bit numbers may be allocated only by an IETF Consensus action.

   Each bit should be tracked with the following qualities:

   - Bit number
   - Capability Description
   - Defining RFC

   Several bits are defined in this document.  The following values have
   been assigned:

      Bit       Capability Description

       0        Path computation with GMPLS link constraints
       1        Bidirectional path computation
       2        Diverse path computation
       3        Load-balanced path computation
       4        Synchronized paths computation
       5        Support for multiple objective functions
       6        Support for additive path constraints
                (max hop count, etc.)
       7        Support for request prioritization
       8        Support for multiple requests per message

8.  Security Considerations

   This document defines OSPF extensions for PCE discovery within an
   administrative domain.  Hence the security of the PCE discovery
   relies on the security of OSPF.

   Mechanisms defined to ensure authenticity and integrity of OSPF LSAs
   [RFC2154], and their TLVs, can be used to secure the PCE Discovery
   information as well.

   OSPF provides no encryption mechanism for protecting the privacy of
   LSAs and, in particular, the privacy of the PCE discovery
   information.








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9.  Manageability Considerations

   Manageability considerations for PCE Discovery are addressed in
   Section 4.10 of [RFC4674].

9.1.  Control of Policy and Functions

   Requirements for the configuration of PCE discovery parameters on
   PCCs and PCEs are discussed in Section 4.10.1 of [RFC4674].

   In particular, a PCE implementation SHOULD allow the following
   parameters to be configured on the PCE:

         - The PCE IPv4/IPv6 address(es) (see Section 4.1).

         - The PCE Scope, including the inter-domain functions
           (inter-area, inter-AS, inter-layer), the preferences,
           and whether the PCE can act as default PCE (see Section 4.2).

         - The PCE-Domains (see Section 4.3).

         - The neighbor PCE-Domains (see Section 4.4).

         - The PCE capabilities (see Section 4.5).

9.2.  Information and Data Model

   A MIB module for PCE Discovery is defined in [PCED-MIB].

9.3.  Liveness Detection and Monitoring

   This document specifies the use of OSPF as a PCE Discovery Protocol.
   The requirements specified in [RFC4674] include the ability to
   determine liveness of the PCE Discovery protocol.  Normal operation
   of the OSPF protocol meets these requirements.

9.4.  Verify Correct Operations

   The correlation of information advertised against information
   received can be achieved by comparing the information in the PCED TLV
   received by the PCC with that stored at the PCE using the PCED MIB
   [PCED-MIB].  The number of dropped, corrupt, and rejected information
   elements are available through the PCED MIB.

9.5.  Requirements on Other Protocols and Functional Components

   The OSPF extensions defined in this document do not imply any
   requirement on other protocols.



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9.6.  Impact on Network Operations

   Frequent changes in PCE information advertised in the PCED TLV, may
   have a significant impact on OSPF and might destabilize the operation
   of the network by causing the PCCs to swap between PCEs.

   As discussed in Section 4.10.4 of [RFC4674], it MUST be possible to
   apply at least the following controls:

      - Configurable limit on the rate of announcement of changed
        parameters at a PCE.

      - Control of the impact on PCCs, such as through rate-limiting
        the processing of PCED TLVs.

      - Configurable control of triggers that cause a PCC to swap to
        another PCE.

10.  Acknowledgments

   We would like to thank Lucy Wong, Adrian Farrel, Les Ginsberg, Mike
   Shand, and Lou Berger for their useful comments and suggestions.

   We would also like to thank Dave Ward, Lars Eggert, Sam Hartman, Tim
   Polk, and Lisa Dusseault for their comments during the final stages
   of publication.

11.  References

11.1.  Normative References

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

   [RFC2154]   Murphy, S., Badger, M., and B. Wellington, "OSPF with
               Digital Signatures", RFC 2154, June 1997.

   [RFC2328]   Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998.

   [RFC2370]   Coltun, R., "The OSPF Opaque LSA Option", RFC 2370, July
               1998.

   [RFC2740]   Coltun, R., Ferguson, D., and J. Moy, "OSPF for IPv6",
               RFC 2740, December 1999.

   [RFC3630]   Katz, D., Kompella, K., and D. Yeung, "Traffic
               Engineering (TE) Extensions to OSPF Version 2", RFC 3630,
               September 2003.



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   [RFC4970]   Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R.,
               and S. Shaffer, "Extensions to OSPF for Advertising
               Optional Router Capabilities", RFC 4970, July 2007.

11.2.  Informative References

   [PCED-MIB]  Stephan, E., "Definitions of Managed Objects for Path
               Computation Element Discovery", Work in Progress, March
               2007.

   [PCEP]      Vasseur, JP., Ed., and JL. Le Roux, Ed., "Path
               Computation Element (PCE) communication Protocol (PCEP)
               ", Work in Progress, November 2007.

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

   [RFC4657]   Ash, J., Ed., and J. Le Roux, Ed., "Path Computation
               Element (PCE) Communication Protocol Generic
               Requirements", RFC 4657, September 2006.

   [RFC4674]   Le Roux, J., Ed., "Requirements for Path Computation
               Element (PCE) Discovery", RFC 4674, October 2006.

   [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, January 2008.























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Authors' Addresses

   Jean-Louis Le Roux (Editor)
   France Telecom
   2, avenue Pierre-Marzin
   22307 Lannion Cedex
   FRANCE
   EMail: jeanlouis.leroux@orange-ftgroup.com


   Jean-Philippe Vasseur (Editor)
   Cisco Systems, Inc.
   1414 Massachusetts Avenue
   Boxborough, MA 01719
   USA
   EMail: jpv@cisco.com


   Yuichi Ikejiri
   NTT Communications Corporation
   1-1-6, Uchisaiwai-cho, Chiyoda-ku
   Tokyo 100-8019
   JAPAN
   EMail: y.ikejiri@ntt.com


   Raymond Zhang
   BT
   2160 E. Grand Ave.
   El Segundo, CA 90025
   USA
   EMail: raymond.zhang@bt.com



















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Full Copyright Statement

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