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Versions: (draft-vasseur-pce-pcep) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 RFC 5440

Networking Working Group                                JP. Vasseur, Ed.
Internet-Draft                                        Cisco Systems, Inc
Expires: December 24, 2006                                   JL. Le Roux
                                                          France Telecom
                                                             A. Ayyangar
                                                        Juniper Networks
                                                                  E. Oki
                                                                     NTT
                                                                A. Atlas
                                                                  Google
                                                             A. Dolganow
                                                                 Alcatel
                                                              Y. Ikejiri
                                          NTT Communications Corporation
                                                               K. Kumaki
                                                        KDDI Corporation
                                                           June 22, 2006


Path Computation Element (PCE) communication Protocol (PCEP) - Version 1
                       draft-ietf-pce-pcep-02.txt

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Copyright Notice



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   Copyright (C) The Internet Society (2006).

Abstract

   This document specifies the Path Computation Element communication
   Protocol (PCEP) for communications between a Path Computation Client
   (PCC) and a Path Computation Element (PCE), or between two PCEs.
   Such interactions include path computation requests and path
   computation replies as well as notifications of specific states
   related to the use of a PCE in the context of MPLS and GMPLS Traffic
   Engineering.  The PCEP protocol is designed to be flexible and
   extensible so as to easily allow for the addition of further messages
   and objects, should further requirements be expressed in the future.

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.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  5
   2.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  5
   3.  Assumptions  . . . . . . . . . . . . . . . . . . . . . . . . .  6
   4.  Transport protocol . . . . . . . . . . . . . . . . . . . . . .  6
   5.  Architectural Protocol Overview (Model)  . . . . . . . . . . .  7
     5.1.  Problem  . . . . . . . . . . . . . . . . . . . . . . . . .  7
     5.2.  Architectural Protocol Overview  . . . . . . . . . . . . .  7
       5.2.1.  Initialization Phase . . . . . . . . . . . . . . . . .  8
       5.2.2.  Path computation request sent by a PCC to a PCE  . . .  9
       5.2.3.  Path computation reply sent by the PCE to a PCC  . . . 10
       5.2.4.  Notification . . . . . . . . . . . . . . . . . . . . . 12
       5.2.5.  Termination of the PCEP Session  . . . . . . . . . . . 13
   6.  PCEP Messages  . . . . . . . . . . . . . . . . . . . . . . . . 14
     6.1.  Common header  . . . . . . . . . . . . . . . . . . . . . . 14
     6.2.  Open message . . . . . . . . . . . . . . . . . . . . . . . 15
     6.3.  Keepalive message  . . . . . . . . . . . . . . . . . . . . 16
     6.4.  Path Computation Request (PCReq) message . . . . . . . . . 17
     6.5.  Path Computation Reply (PCRep) message . . . . . . . . . . 18
     6.6.  Notification (PCNtf) message . . . . . . . . . . . . . . . 19
     6.7.  Error (PCErr) Message  . . . . . . . . . . . . . . . . . . 20
     6.8.  Close message  . . . . . . . . . . . . . . . . . . . . . . 21
   7.  Object Formats . . . . . . . . . . . . . . . . . . . . . . . . 21
     7.1.  Common object header . . . . . . . . . . . . . . . . . . . 21
     7.2.  OPEN object  . . . . . . . . . . . . . . . . . . . . . . . 23
     7.3.  RP Object  . . . . . . . . . . . . . . . . . . . . . . . . 24
       7.3.1.  Object definition  . . . . . . . . . . . . . . . . . . 24
       7.3.2.  Handling of the RP object  . . . . . . . . . . . . . . 26
     7.4.  NO-PATH Object . . . . . . . . . . . . . . . . . . . . . . 27
     7.5.  END-POINT Object . . . . . . . . . . . . . . . . . . . . . 28
     7.6.  BANDWIDTH Object . . . . . . . . . . . . . . . . . . . . . 29
     7.7.  METRIC Object  . . . . . . . . . . . . . . . . . . . . . . 30
     7.8.  ERO Object . . . . . . . . . . . . . . . . . . . . . . . . 32
     7.9.  RRO Object . . . . . . . . . . . . . . . . . . . . . . . . 33
     7.10. LSPA Object  . . . . . . . . . . . . . . . . . . . . . . . 33
     7.11. IRO Object . . . . . . . . . . . . . . . . . . . . . . . . 35
     7.12. SVEC Object  . . . . . . . . . . . . . . . . . . . . . . . 36
       7.12.1. Independent versus synchronized path computation
               requests . . . . . . . . . . . . . . . . . . . . . . . 36
       7.12.2. SVEC Object  . . . . . . . . . . . . . . . . . . . . . 37
       7.12.3. Handling of the SVEC Object  . . . . . . . . . . . . . 38
     7.13. NOTIFICATION Object  . . . . . . . . . . . . . . . . . . . 39
     7.14. PCEP-ERROR Object  . . . . . . . . . . . . . . . . . . . . 42
     7.15. CLOSE Object . . . . . . . . . . . . . . . . . . . . . . . 44
   8.  Manageability Considerations . . . . . . . . . . . . . . . . . 45
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 45
     9.1.  TCP Port . . . . . . . . . . . . . . . . . . . . . . . . . 45



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     9.2.  PCEP Messages  . . . . . . . . . . . . . . . . . . . . . . 45
     9.3.  PCEP Object  . . . . . . . . . . . . . . . . . . . . . . . 46
     9.4.  Notification . . . . . . . . . . . . . . . . . . . . . . . 47
     9.5.  PCEP Error . . . . . . . . . . . . . . . . . . . . . . . . 48
   10. PCEP Finite State Machine (FSM)  . . . . . . . . . . . . . . . 49
   11. Security Considerations  . . . . . . . . . . . . . . . . . . . 54
     11.1. PCEP Authentication and Integrity  . . . . . . . . . . . . 55
     11.2. PCEP Privacy . . . . . . . . . . . . . . . . . . . . . . . 55
     11.3. Protection against Denial of Service attacks . . . . . . . 55
     11.4. Request input shaping/policing . . . . . . . . . . . . . . 56
   12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 56
   13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 56
     13.1. Normative References . . . . . . . . . . . . . . . . . . . 56
     13.2. Informative References . . . . . . . . . . . . . . . . . . 57
   Appendix A.  Proposed Status and Discussion [To Be Removed
                Upon Publication] . . . . . . . . . . . . . . . . . . 58
   Appendix B.  Compliance with the PCECP Requirement Document  . . . 58
   Appendix C.  PCEP Variables  . . . . . . . . . . . . . . . . . . . 59
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 60
   Intellectual Property and Copyright Statements . . . . . . . . . . 62































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1.  Terminology

   Terminology used in this document

   Explicit path: full explicit path from start to destination made of a
   list of strict hops where a hop may be an abstract node such as an
   AS.

   IGP Area: OSPF Area or IS-IS level.

   Inter-domain TE LSP: A TE LSP whose path transits across at least two
   different domains where a domain can either be an IGP area, an
   Autonomous System or a sub-AS (BGP confederations).

   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.

   PCEP Peer: an element involved in a PCEP session (i.e. a PCC or the
   PCE).

   TED: Traffic Engineering Database which contains the topology and
   resource information of the domain.  The TED may be fed by IGP
   extensions or potentially by other means.

   TE LSP: Traffic Engineering Label Switched Path.

   Strict/loose path: mix of strict and loose hops comprising of at
   least one loose hop representing the destination where a hop may be
   an abstract node such as an AS.

   Within this document, when PCE-PCE communications are being
   described, the requesting PCE fills the role of a PCC.  This provides
   a saving in documentation without loss of function.


2.  Introduction

   [I-D.ietf-pce-architecture]describes the motivations and architecture
   for a PCE-based model for the computation of MPLS and GMPLS TE LSPs.
   The model allows the separation of PCE from PCC, and allows
   cooperation between PCEs.  This necessitates a communication protocol
   between PCC and PCE, and between PCEs.

   [I-D.ietf-pce-comm-protocol-gen-reqs] states the generic requirements



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   for such a protocol including the requirement for using the same
   protocol between PCC and PCE, and between PCEs.  Additional
   application-specific requirements (for scenarios such as inter-area,
   inter-AS, etc.) are not included in [I-D.ietf-pce-comm-protocol-gen-
   reqs], but there is a requirement that any solution protocol must be
   easily extensible to handle other requirements as they are introduced
   in application-specific requirements documents.  Examples of such
   application-specific requirements are [I-D.ietf-pce-pcecp-interarea-
   reqs]and [I-D.ietf-pce-inter-layer-req].

   This document specifies the Path Computation Element communication
   Protocol (PCEP) for communications between Path Computation Client
   (PCC) and a Path Computation Element (PCE),or between two PCEs.  Such
   interactions include path computation requests and path computation
   replies as well as notifications of specific states related to the
   use of a PCE in the context of MPLS and GMPLS Traffic Engineering.
   The PCEP protocol is designed to be flexible and extensible so as to
   easily allow for the addition of further messages and objects, should
   further requirements be expressed in the future.


3.  Assumptions

   [I-D.ietf-pce-architecture] describes various types of PCE.  PCEP
   does not make any assumption and thus does not impose any constraint
   on the nature of the PCE.

   Moreover, it is assumed that the PCE gets the required information so
   as to perform TE LSP path computation which usually requires network
   topology and resource information that can be gathered by routing
   protocols or by some other means.  The retrieval of such information
   is out of the scope of this document.

   Similarly, no assumption is made on the discovery method used by a
   PCC to discover a set of PCEs (e.g. via static configuration or
   dynamic discovery) and on the PCE decision selection process.  For
   the sake of reference [I-D.ietf-pce-discovery-reqs] defines a list of
   requirements for dynamic PCE discovery and IGP-based solution for
   such PCE discovery are specified in [I-D.ietf-pce-disco-proto-igp].


4.  Transport protocol

   PCEP operates over TCP using a well-known TCP port (to be assigned by
   IANA).  This allows the requirements of reliable messaging and flow
   control to be met without further protocol work.

   An implementation may decide to keep the TCP session alive for an



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   unlimited time (this may for instance be appropriate when path
   computation requests are sent on a frequent basis so as to avoid to
   open a TCP session each time a path computation request is needed).
   Conversely, in some other circumstances, it may be desirable to
   systematically open and close the TCP connection for each PCEP
   request (for instance when sending of path computation request is a
   rare event).


5.  Architectural Protocol Overview (Model)

   The aim of this section is to describe the PCEP protocol model in the
   spirit of [RFC4101].  An architecture protocol overview (the big
   picture of the protocol) is provided in this section.  Protocol
   details can be found in further sections.

5.1.  Problem

   The PCE-based architecture used for the computation of MPLS and GMPLS
   TE LSP paths is described in [I-D.ietf-pce-architecture].  When the
   PCC and the PCE are not collocated, a communication protocol between
   the PCC and the PCE is required.  PCEP is such a protocol designed
   specifically for communications between a PCC and a PCE or between
   two PCEs: a PCC may use PCEP to send a path computation request for
   one or more TE LSP(s) to a PCE and such a PCE may reply with a set of
   computed path(s) if one or more path(s) obeying the set of
   constraints can be found.

5.2.  Architectural Protocol Overview

   PCEP operates over TCP, which allows the requirements of reliable
   messaging and flow control to be met without further protocol work.

   Several PCEP messages are defined:

   - Open and Keepalive messages are used to initiate and maintain a
   PCEP session respectively.

   - PCReq: a PCEP message sent by a PCC to a PCE to request a path
   computation.

   - PCRep: a PCEP message sent by a PCE to a PCC in reply to a path
   computation request.  A PCRep message can either contain a set of
   computed path(s) if the request could be satisfied or a negative
   reply otherwise.

   - PCNtf: a PCEP notification message either sent by a PCC to a PCE or
   a PCE to a PCC to notify of specific event.



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   - PCErr: a PCEP message sent upon the occurrence of a protocol error
   condition.

   - Close message: a message used to close a PCEP session.

   The set of available PCE(s) may be either statically configured on a
   PCC or dynamically discovered (the mechanism for that discovery is
   out of the scope of this document).  Note that the PCE selection
   algorithm is out of the scope of this document.

   A PCC may have PCEP sessions with more than one PCE and similarly a
   PCE may have PCEP sessions with multiple PCCs.

   A PCEP session establishment is always triggered by the PCC.

5.2.1.  Initialization Phase

   The initialization phase consists of two successive steps (described
   in a schematic form in Figure 1):

   1) Establishment of a TCP connection (3-way handshake) between the
   PCC and the PCE.

   2) Establishment of a PCEP session over the TCP connection.

   Once the TCP connection is established, the PCC and the PCE (also
   referred to as "PCEP peers") initiate a PCEP session establishment
   during which various session parameters are negotiated.  These
   parameters are carried within Open messages and include the keepalive
   timer and, potentially, other detailed capabilities and policy rules
   that specify the conditions under which path computation requests may
   be sent to the PCE.  If the PCEP session establishment phase fails
   because the PCEP peers disagree on the exchanged parameters or one of
   the PCEP peers does not answer after the expiration of the
   establishment timer, the TCP connection is immediately closed.
   Successive retries are permitted but an implementation SHOULD make
   use of exponential back-off.

   Keepalive messages are used to acknowledge Open messages and once the
   PCEP session has been successfully established, Keepalive messages
   are exchanged between PCEP peers to ensure the liveness of the PCEP
   session.

   Details about the Open message and the Keepalive messages can be
   found in .  (Section 6.2) and Section 6.3respectively.






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            +-+-+                  +-+-+
            |PCC|                  |PCE|
            +-+-+                  +-+-+
              |                      |
              |---- Open message --->|
              |                      |
              |<--- Open message ----|
              |                      |
              |                      |
              |                      |
              |<--- Keepalive -------|
              |                      |
              |---- Keepalive ------>|

   Figure 1: PCEP Initialization phase (triggered by a PCC)


5.2.2.  Path computation request sent by a PCC to a PCE



                    +-+-+                  +-+-+
                    |PCC|                  |PCE|
                    +-+-+                  +-+-+
   1)Path computation |                      |
   event              |                      |
   2)PCE Selection    |                      |
   3)Path computation |---- PCReq message--->|
   request sent to    |                      |
   the selected PCE   |                      |

                  Figure 2: Path computation request

   Once a PCC (or a PCE) has successfully established a PCEP session
   with one or more PCEs, if an event is triggered that requires the
   computation of a set of path(s), the PCC first selects one of more
   PCE(s) to send the request to.  Note that the PCE selection decision
   process may have taken place prior to the PCEP session establishment.

   Once the PCC has selected a PCE, it sends a path computation request
   to the PCE (PCReq message) that contains a variety of objects that
   specify the set of constraints and attributes for the path to be
   computed.  For example "Compute a TE LSP path with source IP
   address=x.y.z.t, destination IP address=x'.y'.z'.t', bandwidth=X
   Mbit/s, Priority=Y, ...".  Additionally, the PCC may desire to
   specify the urgency of such request by assigning a request priority.
   Each request is uniquely identified by a request-id number and the
   PCC-PCE addresses pair.  The process is shown in a schematic form in



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   figure 2.

   Details about the PCReq message can be found in Section 6.4

5.2.3.  Path computation reply sent by the PCE to a PCC














































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                 +-+-+                  +-+-+
                 |PCC|                  |PCE|
                 +-+-+                  +-+-+
                   |                      |
                   |---- PCReq message--->|
                   |                      |1) Path computation
                   |                      |request received
                   |                      |
                   |                      |2)Path successfully
                   |                      |computed
                   |                      |
                   |                      |3) Computed path(s) sent
                   |                      |to the PCC
                   |<--- PCRep message ---|
                   |    (Positive reply)  |

    Figure 3a: Path computation request with successful path computation

                 +-+-+                  +-+-+
                 |PCC|                  |PCE|
                 +-+-+                  +-+-+
                   |                      |
                   |                      |
                   |---- PCReq message--->|
                   |                      |1) Path computation
                   |                      |request received
                   |                      |
                   |                      |2) No Path found that
                   |                      |satisfies the request
                   |                      |
                   |                      |3) Negative reply sent to
                   |                      |the PCC (optionally with
                   |                      |various additional
                   |                      |information)
                   |<--- PCRep message ---|
                   |   (Negative reply)   |

    Figure 3b: Path computation request with unsuccessful path computation
   Upon receiving a path computation request from a PCC, the PCE
   triggers a path computation, the result of which can either be:

   - Positive (Figure 3-a): the PCE manages to compute a path satisfying
   the set of required constraints.  The PCE returns the set of computed
   path(s) to the requesting PCC.  Note that PCEP supports the
   capability to send a single request which refers to the computation
   of multiple paths: for example, compute two link-diverse paths.

   - Negative (Figure 3-b): no path could be found that satisfies the



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   set of constraints.  In this case, a PCE may provide the set of
   constraints that led to the path computation failure.  Upon receiving
   a negative reply, a PCC may decide to resend a modified request or
   take any other appropriate action.

   Details about the PCRep message can be found in Section 6.5.

5.2.4.  Notification

   There are several circumstances whereby a PCE may want to notify a
   PCC of a specific event.  For example, suppose that the PCE suddenly
   experiences some congestion that would lead to unacceptable response
   times.  The PCE may want to notify one or more PCCs that some of
   their requests (listed in the notification) will not be satisfied or
   may experience unacceptable delays.  Such notification may
   potentially result in path computation redirections on the PCC
   towards another PCE, if an alternate PCE is available.  Similarly, a
   PCC may desire to notify a PCE of particular event such as the
   cancellation of pending request(s).
































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                    +-+-+                  +-+-+
                    |PCC|                  |PCE|
                    +-+-+                  +-+-+
   1)Path computation |                      |
   event              |                      |
   2)PCE Selection    |                      |
   3)Path computation |---- PCReq message--->|
   request X sent to  |                      |4) Path computation
   the selected PCE   |                      |triggered
                      |                      |
                      |                      |
   5) Path computation|                      |
   request X cancelled|                      |
                      |---- PCNtf message -->|
                      |                      |6) Path computation
                      |                      |request X cancelled

   Figure 4: Example of PCC notification (request cancellation) sent to a PCE


                    +-+-+                  +-+-+
                    |PCC|                  |PCE|
                    +-+-+                  +-+-+
   1)Path computation |                      |
   event              |                      |
   2)PCE Selection    |                      |
   3)Path computation |---- PCReq message--->|
   request X sent to  |                      |4) Path computation
   the selected PCE   |                      |triggered
                      |                      |
                      |                      |
                      |                      |5) PCE experiencing
                      |                      |congestion
                      |                      |
                      |                      |6) Path computation
                      |                      |request X cancelled
                      |                      |
                      |<--- PCNtf message----|


   Figure 5: Example of PCE notification (request(s) cancellation) sent to a PCC

   Details about the PCNtf message can be found in Section 6.6.

5.2.5.  Termination of the PCEP Session

   When one of the PCEP peers desires to terminate a PCEP session it
   first sends a PCEP Close message and then close the TCP connection.



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   If the PCEP session is terminated by the PCE, the PCC clears all the
   states related to pending requests sent to the PCE.  Similarly, if
   the PCC terminates a PCEP session the PCE clears all pending path
   computation requests sent by the PCC in question as well as the
   related states.  A Close message can only be sent to terminate a PCEP
   session if the PCEP session has previously been established.

   In case of TCP connection failure, the PCEP session SHOULD be
   maintained for a period of time equal to the Deadtimer.

   Details about the Close message can be found in Section 6.8.


6.  PCEP Messages

   A PCEP message consists of a common header followed by a variable
   length body made of a set of objects that can either be mandatory or
   optional.  In the context of this document, an object is said to be
   mandatory in a PCEP message when the object must be included in such
   message for the message to be considered as valid.  Thus a missing
   mandatory object in a PCEP message MUST be considered as a malformed
   message and such condition MUST trigger an Error message.
   Conversely, if an object is optional, the object may or may not be
   present.

   A flag referred to as the P flag is defined in the common header of
   each PCEP object (see Section 7.1) that can be set by a PCEP peer to
   enforce a PCE to take into account the related information during the
   path computation.  For example, the COST object allows a PCC to
   specify a bounded acceptable path cost.  The COST object is optional
   but a PCC may set a flag to ensure that such constraint is taken into
   account.  Similarly to the previous case, if such constraint cannot
   be taken into account by the PCE, this should trigger an Error
   message.

   For each PCEP message type a set of rules is defined which specifies
   the set of possible objects that the message can carry.  We use the
   Backus-Naur Form (BNF) to specify such rules.  Square brackets refer
   to optional sub-sequences.  An implementation MUST form the PCEP
   messages using the order specified in this document.

6.1.  Common header









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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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Ver  |     Flags     | Message-Type  |        Reserved       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                          Message-Lenght                       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                Figure 6: PCEP message common header
   Ver (Version - 4 bits): PCEP protocol version number.  Current
   version is version 1.

   Flags (8 bits): no flags are currently defined.

   Message-Type (8 bits):

   The following message types are currently defined (to be confirmed by
   IANA).
   Value    Meaning
     1        Open
     2        Keepalive
     3        Path Computation Request
     4        Path Computation Reply
     5        Notification
     6        Error
     7        Close
   Message Length (32 bits): total length of the PCEP message expressed
   in bytes including the common header.

6.2.  Open message

   The Open message is a PCEP message sent by a PCC to a PCE in order to
   establish a PCEP session.  The Message-Type field of the PCEP common
   header for the Open message is set to 1 (To be confirmed by IANA).

   Once the TCP connection has been successfully established, the first
   message sent by the PCC to the PCE or by the PCE to the PCC MUST be
   an Open message.  Any message received prior to an OPEN message MUST
   trigger a protocol error condition and the PCEP session MUST be
   terminated.  The Open message is used to establish a PCEP session
   between the PCEP peers.  During that phase the PCEP peers exchange
   several session characteristics.  If both parties agree on such
   characteristics the PCEP session is successfully established.








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   Open message
   <Open Message>::= <Common Header>
                     <OPEN>
   The Open message MUST contain exactly one OPEN object (see
   Section 7.2).  Various session characteristics are specified within
   the OPEN object.

   Once an Open message has been sent to a PCEP peer, the sender MUST
   start an initialization timer called InitOpen after the expiration of
   which a similar Open message MUST be resent if no reply has been
   received from the PCEP peer.  The InitOpen timer has a fixed value of
   1 minute.  The maximum number of Open messages named MaxRetryOpen
   that can be sent without any response from the PCEP peer is equal to
   3.

   Upon the receipt of an Open message, the receiving PCEP peer MUST
   determine whether the suggested PCEP session characteristics are
   acceptable.  If at least one of the characteristic(s) is not
   acceptable by the receiving peer, it MUST send an Error message.  The
   Error message SHOULD also contain the related Open object: for each
   unacceptable session parameter, an acceptable parameter value SHOULD
   be proposed in the appropriate field of the Open object in place of
   the originally proposed value.  The PCEP peer MAY decide to resend an
   Open message with different session characteristics.  If a second
   Open message is received with the same set of parameters or with
   parameters that are still unacceptable, the receiving peer MUST send
   an Error message and it MUST immediately close the TCP connection.
   Details about error message can be found in Section 7.14.

   If the PCEP session characteristics are acceptable, the receiving
   PCEP peer MUST consequently send a Keepalive message (defined in
   Section 6.3) that would serve as acknowledgment.

   The PCEP session is considered as established once both PCEP peers
   have received a Keepalive message from their peer.

6.3.  Keepalive message

   A Keepalive message is a PCEP message sent by a PCC or a PCE in order
   to keep the session in active state.  The Message-Type field of the
   PCEP common header for the Keepalive message is set to 2 (To be
   confirmed by IANA).  The Keepalive message does not contain any
   object.

   Keepalive: PCEP has its own keepalive mechanism used to ensure of the
   liveness of the PCEP session.  This requires the determination of the
   frequency at which each PCEP peer sends keepalive messages.
   Asymmetric values may be chosen; thus there is no constraints



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   mandating the use of identical keepalive frequencies by both PCEP
   peers.  The DeadTimer is defined as the period of time after the
   expiration of which a PCEP peer declares the session down if no PCEP
   message has been received (keepalive or any other PCEP message: thus,
   any PCEP message acts as a keepalive message).  Similarly, there is
   no constraints mandating the use of identical DeadTimers by both PCEP
   peers.  The minimum KeepAliveTimer value is 1 second.

   Keepalive messages are used either to acknowledge an Open message if
   the receiving PCEP peer agrees on the session characteristics and to
   ensure the liveness of the PCEP session.  Keepalive messages are sent
   at the frequency specified in the OPEN object carried within an Open
   message.  Because any PCEP message may serve as Keepalive an
   implementation may either decide to send Keepalive messages at the
   same frequency regardless on whether other PCEP messages might have
   been sent since the last sent Keepalive message or may decide to
   differ the sending of the next Keepalive message based on the time at
   which the last PCEP message (other than Keepalive) was sent.

   Keepalive message
   <Keepalive Message>::= <Common Header>

6.4.  Path Computation Request (PCReq) message

   A Path Computation Request message (also referred to as a PCReq
   message) is a PCEP message sent by a PCC to a PCE so as to request a
   path computation.  The Message-Type field of the PCEP common header
   for the PCReq message is set to 3 (To be confirmed by IANA).

   There are two mandatory objects that MUST be included within a PCReq
   message: the RP and the END-POINTS objects (see section 7).  If one
   of these objects is missing, the receiving PCE MUST send an error
   message to the requester.  Other objects are optional.


















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   The format of a PCReq message is as follows:
   <PCReq Message>::= <Common Header>
                      [<SVEC-list>]
                      <request-list>

   where:
      <svec-list>::=<SVEC>[<svec-list>]
      <request-list>::=<request>[<request-list>]

      <request>::= <RP>
                   [<END-POINTS>]
                   [<LSPA>]
                   [<BANDWIDTH>]
                   [<METRIC>]
                   [<RRO>]
                   [<BANDWIDTH>]
                   [<IRO>]
   The SVEC, RP, END-POINTS, LSPA, BANDWIDTH, METRIC, ERO, and IRO
   objects are defined in Section 7.  The special case of two BANDWIDTH
   objects in details inSection 7.6.

6.5.  Path Computation Reply (PCRep) message

   The PCEP Path Computation Reply message (also referred to as a PCRep
   message) is a PCEP message sent by a PCE to a requesting PCC in
   response to a previously received PCReq message.  The Message-Type
   field of the PCEP common header is set to 4 (To be confirmed by
   IANA).

   The PCRep message MUST contain at least one RP object.  For each
   reply that is bundled into a single PCReq message, an RP object MUST
   be included that contains a Request-ID-number identical to the one
   specified in the RP object carried in the corresponding PCReq message
   (see Section 7.3for the definition of the RP object).

   A PCRep may comprise multiple computed path(s) corresponding to
   multiple path computation requests originated by a common requesting
   PCC and/or to multiple acceptable paths corresponding to the same
   request.  The bundling of multiple responses within a single PCRep
   message is supported by the PCEP protocol.  If a PCE receives non-
   synchronized path computation requests by means of one or more PCReq
   messages from a requesting PCC it may decide to bundle the computed
   paths within a single PCRep message so as to reduce the control plane
   load.  Note that the counter side of such an approach is the
   introduction of additional delays for some path computation requests
   of the set.  Conversely, a PCE that receives multiple requests within
   the same PCReq message, may decide to reply each path in separate
   PCRep messages.



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   If the path computation request can be successfully satisfied (the
   PCE manages to compute a set of path(s) that obey the requested
   constraint(s)), the set of computed path(s) specified by means of ERO
   object(s) is inserted in the PCRep message.  The ERO object is
   defined in Section 7.8.  Such a situation where multiple computed
   paths are provided in a PCRep message is discussed in detail in
   Section 7.12.

   If the path computation request cannot be satisfied, the PCRep
   message MUST include a NO-PATH object.  The NO-PATH object (further
   described in Section 7.4) may also comprise other information (e.g
   reasons for the path computation failure).

   The format of a PCRep message is as follows:
   <PCRep Message> ::= <Common Header>
                       [<svec-list>]
                       <response-list>

   where:
      <svec-list>::=<SVEC>[<svec-list>]
      <response-list>::=<response>[<response-list>]


      <response>::=<RP>
                  [<NO-PATH>]
                  [<path-list>]

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

      <path>::= <ERO>
               [<LSPA>]
               [<BANDWIDTH>]
               [<METRIC>]
               [<IRO>]


6.6.  Notification (PCNtf) message

   The PCEP Notification message (also referred to as the PCNtf message)
   can either be sent by a PCE to a PCC or by a PCC to a PCE so as to
   notify of a specific event.  The Message-Type field of the PCEP
   common header is set to 5 (To be Confirmed by IANA).

   The PCNtf message MUST carry at least one NOTIFICATION object and may
   contain several NOTIFICATION objects should the PCE or the PCC intend
   to notify of multiple events.  The NOTIFICATION object is defined in
   Section 7.13.  The PCNtf message may also contain an RP object (see
   Section 7.3when the notification refers to a particular path



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   computation request.

   The PCNtf message may be sent by a PCC or a PCE in response to a
   request or in an unsolicited manner.

   The format of a PCNtf message is as follows:
   <PCNtf Message>::=<Common Header>
                     <notify-list>

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

   <notify>::= [<request-id-list>]
                <notification-list>

   <request-id-list>:==<RP><request-id-list>

   <notification-list>:=<NOTIFICATION><notification-list>

6.7.  Error (PCErr) Message

   The PCEP Error message (also referred to as a PCErr message) is sent
   when a protocol error condition is met.  The Message-Type field of
   the PCEP common header is set to 6.

   The PCErr message may be sent by a PCC or a PCE in response to a
   request or in an unsolicited manner.  In the former case, the PCErr
   message MUST include the set of RP objects related to the pending
   path computation request(s) which triggered the protocol error
   condition.  In the later case (unsolicited), no RP object is inserted
   within the PCErr message.  No RP object is inserted in a PCErr when
   the error condition occurred during the initialization phase.  A
   PCErr message MUST comprise a PCEP-ERROR object specifying the PCEP
   error condition.  The PCEP-ERROR object is defined in section
   Section 7.14.

















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   The format of a PCErr message is as follows:
   <PCErr Message> ::= <Common Header>
                       <error-list>
                       [<Open>]

   <error-list>:==<error>[<error-list>]
   <error>::=[<request-id-list>]
              <error-obj-list>

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

   <error-obj-list>:==<PCEP-ERROR>[<error-obj-list>]
   The procedure upon the reception of a PCErr message is defined in
   Section 7.14.

6.8.  Close message

   The Close message is a PCEP message sent by either a PCC to a PCE or
   by a PCE to a PCC in order to close a PCEP session.  The Message-Type
   field of the PCEP common header for the Open message is set to 7 (To
   be confirmed by IANA).

   Close message
   <Close Message>::= <Common Header>
                     <CLOSE>
   The Close message MUST contain exactly one CLOSE object (see
   Section 6.8).

   Upon the receipt of a Close message, the receiving PCEP peer MUST
   cancel all pending requests and MUST close the TCP connection.


7.  Object Formats

7.1.  Common object header
















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   A PCEP object carried within a PCEP message consists of one or more
   32-bit words with a common header which has the following format:
    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Object-Class  |   OT  |Res|P|I|   Object Length (bytes)       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   //                        (Object body)                        //
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                    Figure 8: PCEP common object header

   Object-Class (8 bits): identifies the PCEP object class.

   OT (Object-Type - 4 bits): identifies the PCEP object type.

   The Object-Class and Object-Type are managed by IANA.

   The Object-Class and Object-Type fields uniquely identify each PCEP
   object.

   Res (3 bits): Reserved.

   P flag (Processing-Rule - 1-bit): the P flag allows a PCC to specify
   in a PCReq message sent to a PCE whether the object must be taken
   into account by the PCE during path computation or is just optional.
   When the P flag is set, the object MUST be taken into account by the
   PCE.  Conversely, when the P flag is cleared, the object is optional
   and the PCE is free to ignore it if not supported.

   I flag (Ignore - 1 bit): the I flag is used by a PCE in a PCRep
   message to indicate to a PCC whether or not an optional object was
   processed.  The PCE MAY include the ignored optional object in its
   reply and set the I flag to indicate that the optional object was
   ignored during path computation.  When the I flag is cleared, the PCE
   indicates that the optional object was processed during the path
   computation.  The setting of the I flag for optional objects is
   purely indicative and optional.  The I flag MUST be cleared if the P
   flag is set.

   If the PCE does not understand an object with the P Flag set or
   understands the object but decides to ignore the object, the entire
   PCEP message MUST be rejected and the PCE MUST send a PCErr message
   with Error-Type="Unknown Object" or "Not supported Object".

   Res flags (2 bits).  Reserved field (MUST be set to 0).



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   Object Length (16 bits).  Specifies the total object length including
   the header, in bytes.  The Object Length field MUST always be a
   multiple of 4, and at least 4.  The maximum object content length is
   65528 bytes.

7.2.  OPEN object

   The OPEN object MUST be present in each Open message and may be
   present in PCErr message.  There MUST be only one OPEN object per
   Open or PCErr message.

   The OPEN object contains a set of fields used to specify the PCEP
   protocol version, Keepalive frequency, PCEP session ID along with
   various flags.  The OPEN object may also contain a set of TLVs used
   to convey various session characteristics such as the detailed PCE
   capabilities, policy rules and so on.  No such TLV is currently
   defined.

   OPEN Object-Class is to be assigned by IANA (recommended value=1)

   OPEN Object-Type is to be assigned by IANA (recommended value=1)

   The format of the OPEN 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Ver |  Keepalive    |  Deadtimer    |      SID      |  Flags  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   //                         Optional TLV(s)                     //
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                    Figure 9: OPEN Object format
   Ver (Ver - 3 bits): PCEP version.  Current version is 1.

   Keepalive (8 bits): minimum period of time (in seconds) between the
   sending of PCEP messages that the sender of the Open message will
   send Keepalive messages.  The minimum value for the Keepalive is 1
   second.  When set to 0, once the session is established, no further
   keepalives need to be sent to the remote peer.  A RECOMMENDED value
   for the keepalive frequency is 30 seconds.

   DeadTimer (8 bits): specifies the amount of time after the expiration
   of which a PCEP peer declares the session with the sender of the Open
   message down if no PCEP message has been received.  The DeadTimer
   MUST be set to 0 if the Keepalive is set to 0.  A RECOMMENDED value
   for the DeadTimer is 4 times the value of the Keepalive.



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   SID (PCEP session-ID - 8 bits): specifies a 2 octet unsigned PCEP
   session number that identifies the current session.  The SID MUST be
   incremented each time a new PCEP session is established and is mainly
   used for logging and troubleshooting purposes.

   Flags (5 bits): No Flags are currently defined.

   Optional TLVs may be included within the OPEN object body to specify
   PCC or PCE characteristics.  The specification of such TLVs is
   outside the scope of this document.

   When present in an Open message, the OPEN object specifies the
   proposed PCEP session characteristics.  Upon receiving unacceptable
   PCEP session characteristics during the PCEP session initialization
   phase, the receiving PCEP peer (PCE), may include a PCEP object
   within the PCErr message so as to propose alternative session
   characteristic values.

7.3.  RP Object

   The RP (Request Parameters) object MUST be carried within each PCReq
   and PCRep messages and MAY be carried within PCNtf and PCErr
   messages.  The P flag of the RP object MUST be set.  The RP object is
   used to specify various characteristics of the path computation
   request.

7.3.1.  Object definition

   RP Object-Class is to be assigned by IANA (recommended value=2)

   RP Object-Type is to be assigned by IANA (recommended value=1)




















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   The format of the RP 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Reserved    |              Flags          |N|O|B|R| Pri |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Request-ID-number                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   //                      Optional TLV(s)                        //
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                  Figure 10: RP object body format

   The RP object body has a variable length and may contain additional
   TLVs.  No TLV is currently defined.

   Flags: 18 bits - The following flags are currently defined:

   Pri (Priority - 3 bits): the Priority field may be used by the
   requesting PCC to specify to the PCE the request's priority from 1 to
   7.  The decision of which priority should be used for a specific
   request is of a local matter and MUST be set to 0 when unused.
   Furthermore, the use of the path computation request priority by the
   PCE's requests scheduler is implementation specific and out of the
   scope of this document.  Note that it is not required for a PCE to
   support the priority field: in that case, the priority field
   RECOMMENDED be set to 0 by the PCC in the RP object.  If the PCE does
   not take into account the request priority, it is RECOMMENDED to set
   the priority field to 0 in the RP object carried within the
   corresponding PCRep message, regardless of the priority value
   contained in the RP object carried within the corresponding PCReq
   message.  A higher numerical value of the priority field reflects a
   higher priority.  Note that it is the responsibility of the network
   administrator to make use of the priority values in a consistent
   manner across the various PCC(s).  The ability of a PCE to support
   requests prioritization may be dynamically discovered by the PCC(s)
   by means of PCE capability discovery.  If not advertised by the PCE,
   a PCC may decide to set the request priority and will learn the
   ability of the PCE the support request prioritization by observing
   the Priority field of the RP object received in the PCRep message.
   If the value of the Pri field is set to 0, this means that the PCE
   does not support the handling of request priorities: in other words,
   the path computation request has been honoured but without taking the
   request priority into account.

   R (Reoptimization - 1 bit): when set, the requesting PCC specifies



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   that the PCReq message relates to the reoptimization of an existing
   TE LSP in which case the path of the existing TE LSP to be
   reoptimized MUST be provided in the PCReq (except of 0-bandwidth TE
   LSP) message by means of an RRO object defined in Section 7.9.

   B (Bi-directional - 1 bit): when set, the PCC specifies that the path
   computation request relates to a bidirectional TE LSP that has the
   same traffic engineering requirements including fate sharing,
   protection and restoration, LSRs, and resource requirements (e.g.
   latency and jitter) in each direction.  When cleared, the TE LSP is
   unidirectional.

   O (strict/lOose - 1 bit): when set, in a PCReq message, this
   indicates that a strict/loose path is acceptable.  Otherwise, when
   cleared, this indicates to the PCE that an explicit path is required.
   In a PCRep message, when the O bit is set this indicates that the
   returned path is strict/loose, otherwise (the O bit is cleared), the
   returned path is explicit.

   F (new - 1 bit): when set, the requesting PCC requires the
   computation of a new path for a TE LSP that has failed in which case
   the path of the existing TE LSP MUST be provided in the PCReq (except
   of 0-bandwidth TE LSP) message by means of an RRO object defined in
   Section 7.9.  This is to avoid double bandwidth booking should the
   TED not be yet updated or the corresponding resources not be yet
   released.

   Request-ID-number (32 bits).  The Request-ID-number value combined
   with the source IP address of the PCC and the PCE address uniquely
   identify the path computation request context.  The Request-ID-number
   MUST be incremented each time a new request is sent to the PCE.  If
   no path computation reply is received from the PCE, and the PCC
   wishes to resend its request, the same Request-ID-number MUST be
   used.  Conversely, different Request-ID-number MUST be used for
   different requests sent to a PCE.  The same Request-ID-number may be
   used for path computation requests sent to different PCEs.  The path
   computation reply is unambiguously identified by the IP source
   address of the replying PCE.

7.3.2.  Handling of the RP object

   If a PCReq message is received without containing an RP object, the
   PCE MUST send a PCErr message to the requesting PCC with Error-
   type="Required Object missing" and Error-value="RP Object missing".

   If the C bit of the RP message carried within a PCReq message is set
   and local policy has been configured on the PCE to not provide the
   computed path cost, a PCErr message MUST be sent by the PCE to the



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   requesting PCC and the pending path computation request MUST be
   discarded.  The Error-type is "Policy Violation" and Error-value is
   "C bit set".

   If the O bit of the RP message carried within a PCReq message is set
   and local policy has been configured on the PCE to not provide
   explicit path(s) (for instance, for confidentiality reasons), a PCErr
   message MUST be sent by the PCE to the requesting PCC and the pending
   path computation request MUST be discarded.  The Error-type is
   "Policy Violation" and Error-value is "O bit set".

   R bit: when the R bit of the RP object is set in a PCReq message,
   this indicates that the path computation request relates to the
   reoptimization of an existing TE LSP.  In this case, the PCC MUST
   provide the explicit or strict/loose path by including an RRO object
   in the PCReq message so as to avoid double bandwidth counting if and
   only if the TE LSP is a non 0-bandwidth TE LSP.  If the PCC has
   previously requested a non-explicit path (O bit set), a
   reoptimization can still be requested by the PCC but this implies for
   the PCE to be either stateful (keep track of the previously computed
   path with the associated list of strict hops) or to have the ability
   to retrieve the complete required path segment.  Alternatively the
   PCC MUST be able to inform PCE of the working path with associated
   list of strict hops in PCReq.  The absence of an RRO in the PCReq
   message for a non 0-bandwidth TE LSP when the R bit of the RP object
   is set MUST trigger the sending of a PCErr message with Error-
   type="Required Object Missing" and Error-value="RRO Object missing
   for reoptimization".

   If the PCC receives a PCRep message that contains a RP object
   referring to an unknown Request-ID-Number, the PCC MUST send a PCErr
   message with Error-Type="Unknown request reference".

7.4.  NO-PATH Object

   The No-PATH object is used in PCRep messages in response to a path
   computation request that was unsuccessful (the PCE could not find a
   path satisfying the set of constraints).  When a PCE cannot find a
   path satisfying a set of constraints, it MUST include a NO-PATH
   object in the PCRep message.  In its simplest form, the NO-PATH
   object is limited to a set of flags and just reports the
   impossibility to find a path that satisfies the set of constraints.
   Optionally, if the PCE supports such capability, the PCRep message
   MAY also contain a list of objects that specify the set of
   constraints that could not be satisfied.  The PCE MAY just replicate
   the object that was received that was the cause of the unsuccessful
   computation or MAY optionally report a suggested value for which a
   path could have been found.



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   NO-PATH Object-Class is to be assigned by IANA (recommended value=3)

   NO-PATH Object-Type is to be assigned by IANA (recommended value=1)

   The format of the NO-PATH 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |C|       Flags                 |          Reserved             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                 Figure 11: NO-PATH object format
   The NO-PATH object body has a fixed length of 4 octets.

   Flags (16 bits).  The following flags are currently defined:

   C flag (1 bit): when set, the PCE indicates the set of unsatisfied
   constraints (reasons why a path could not be found) in the PCRep
   message by including the relevant PCEP objects.  When cleared, no
   reason is specified.

   Example: consider the case of a PCC that sends a path computation
   request to a PCE for a TE LSP of X MBits/s.  Suppose that PCE cannot
   find a path for X MBits/s.  In this case, the PCE must include in the
   PCRep message a NO-PATH object.  Optionally the PCE may also include
   the original BANDWIDTH object so as to indicate that the reasons for
   the unsuccessful computation is the bandwidth constraint (in this
   case, the C flag is set).  If the PCE supports such capability it may
   alternatively include the BANDWIDTH Object and report a value of Y in
   the bandwidth field of the BANDWIDTH object (in this case, the C flag
   is set).

   When the NO-PATH object is absent from a PCRep message, the path
   computation request has been fully satisfied and the corresponding
   path(s) is/are provided in the PCRep message.

7.5.  END-POINT Object

   The END-POINTS object is used in a PCReq message to specify the
   source IP address and the destination IP address of the path for
   which a path computation is requested.  Note that the source and
   destination addresses specified in the END-POINTS object may or may
   not correspond to the source and destination IP address of the TE LSP
   but rather to a path segment.  Two END-POINTS objects (for IPv4 and
   IPv6) are defined.

   END-POINTS Object-Class is to be assigned by IANA (recommended
   value=4)



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   END-POINTS Object-Type is to be assigned by IANA (recommended value=1
   for IPv4 and 2 for IPv6)

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

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

              Figure 12: END-POINTS object body format for IPv4

   The format of the END-POINTS object 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   |                Source IPv6 address (16 bytes)                 |
   |                                                               |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   |              Destination IPv6 address (16 bytes)              |
   |                                                               |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

              Figure 13: END-POINTS object body format for IPv6

   The END-POINTS object body has a fixed length of 8 octets for IPv4
   and 32 octets for IPv6.

7.6.  BANDWIDTH Object

   The BANDWIDTH object is optional and can be used to specify the
   requested bandwidth for a TE LSP.  In the case of a non existing TE
   LSP, the BANDWIDTH object MUST be included in the PCReq message so as
   to specify the required bandwidth for the new TE LSP.  In the case of
   the reoptimization of an existing TE LSP, the bandwidth of the
   existing TE LSP MUST also be included in addition to the requested
   bandwidth if and only if the two values differ.  Consequently, two
   Object-Type are defined that refer to the requested bandwidth and the
   bandwidth of a existing TE LSP for which a reoptimization is being



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   performed.

   The BANDWIDTH object may be carried within PCReq and PCRep messages.
   The absence of the BANDWIDTH object MUST be interpreted by the PCE as
   a path computation request related to a 0 bandwidth TE LSP.

   BANDWIDTH Object-Class is to be assigned by IANA (recommended
   value=5)

   Two Object-Type are defined for the BANDWIDTH object:

   o  Requested bandwidth: BANDWIDTH Object-Type is to be assigned by
      IANA (recommended value=1)

   o  Bandwidth of an existing TE LSP for which a reoptimization is
      performed.  BANDWIDTH Object-Type is to be assigned by IANA
      (recommended value=2)

   The format of the BANDWIDTH 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Bandwidth                              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                Figure 14: BANDWIDTH object body format
   Bandwidth: 32 bits.  The requested bandwidth is encoded in 32 bits in
   IEEE floating point format, expressed in bytes per second.

   The BANDWIDTH object body has a fixed length of 4 octets.

7.7.  METRIC Object

   The METRIC object is optional and can be used for several purposes.

   In a PCReq message, a PCC MAY insert a METRIC object:

   o  To indicate the metric that must be optimized by the path
      computation algorithm.  Currently, two metrics are defined: the
      IGP cost and the TE metric (see [RFC3785]).

   o  To indicate a bound on the path cost than must not be exceeded for
      the path to be considered as acceptable by the PCC.

   In a PCRep message, the METRIC object MAY be inserted so as to
   provide the cost for the computed path.  It MAY also be inserted
   within a PCRep with the NO-PATH object, to indicate that the metric
   constraint could not be satisfied.



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   The path computation algorithmic aspects used by the PCE to optimize
   a path with respect to a specific metric are outside the scope of
   this document.

   It must be understood that such path metric is only meaningful if
   used consistently: for instance, if the delay of a path computation
   segment is exchanged between two PCE residing in different domains,
   consistent ways of defining the delay must be used.

   The absence of the METRIC object MUST be interpreted by the PCE as a
   path computation request for which the PCE may choose the metric to
   be used.

   METRIC Object-Class is to be assigned by IANA (recommended value=6)

   METRIC Object-Type is to be assigned by IANA (recommended value=1)

   The format of the METRIC 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Reserved             |         Flags       |C|B|  T  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          metric-value                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                   Figure 15: METRIC object body format

   T (Type - 3 bits): Specifies the metric type.  Two values are
   currently defined:

   o  T=1: The IGP metric

   o  T=2: The TE cost

   B (Bound - 1 bit): When set in a PCReq message, the metric-value
   indicates a bound (a maximum) for the path cost that must not be
   exceeded for the PCC to consider the computed path as acceptable.
   When the B flag is cleared, the metric-value field MUST be set to
   0x0000.  In a PCReq message, if the B-flag is cleared, then the
   metric-value field MUST be set to 0.  The B flag MUST always be
   cleared in a PCRep message.

   C (Cost - 1 bit): When set in a PECReq message, this indicates that
   the PCE MUST provide the computed path cost (should a path satisfying
   the constraints be found) in the PCRep message with regards to the
   corresponding metric.




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   Metric-value (32 bits): metric value encoded in 32 bits in IEEE
   floating point format.

   The METRIC object body has a fixed length of 8 octets.

   Multiple METRIC Objects MAY be inserted in a PCRep or the PCReq
   message.

   In a PCReq message the presence of multiple METRIC object can be used
   to specify a multi-parameters (e.g. a metric may be a constraint or a
   parameter to minimize/maximize) objective function or multiple bounds
   for different constraints.

   In a PCRep message, unless not allowed by PCE policy, at least one
   METRIC object MUST be present that reports the computed path cost if
   the C bit of the RP object was set in the corresponding path
   computation request (the B-flag MUST be cleared); optionally the
   PCRep message may contain additional METRIC objects that correspond
   to bound constraints, in which case the metric-value MUST be equal to
   the corresponding path metric cost (the B-flag MUST be set).  If no
   path satisfying the constraints could be found by the PCE, the METRIC
   objects MAY also be present in the PCRep message with the NO-PATH
   object, to indicate a constraint metric (B-Flag was set in the path
   computation request) that cannot be satisfied.

   Example: if a PCC sends a path computation request to a PCE where the
   metric to optimize is the IGP metric and the TE metric must not
   exceed the value of M, two METRIC object are inserted in the PCReq
   message:

   o  First METRIC Object with B=0, T=1, metric-value=0x0000

   o  Second METRIC Object with B=1, T=2, metric-value=M

   If a path satisfying the set of constraints can be found by the PCE
   and no policy preventing to provide the path cost in place, the PCE
   inserts one METRIC object with B=0, T=1, metric-value= computed IGP
   path cost.  Additionally, the PCE may insert a second METRIC object
   with B=1, T=2, metric-value= computed TE path cost.

7.8.  ERO Object

   The ERO object is used to encode a TE LSP.  The ERO Object is carried
   within a PCRep message to provide the computed TE LSP should have the
   path computation been successful.

   The contents of this object are identical in encoding to the contents
   of the Explicit Route Object defined in [RFC3209], [RFC3473] and



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   [RFC3477].  That is, the object is constructed from a series of sub-
   objects.  Any RSVP ERO sub-object already defined or that could be
   defined in the future for use in the ERO is acceptable in this
   object.

   PCEP ERO sub-object types correspond to RSVP ERO sub-object types.

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

   ERO Object-Class is to be assigned by IANA (recommended value=7)

   ERO Object-Type is to be assigned by IANA (recommended value=1)

7.9.  RRO Object

   The RRO object is used to record the route followed by a TE LSP.  The
   PCEP RRO object is exclusively carried within a PCReq message so as
   to specify the route followed by a TE LSP for which a reoptimization
   is desired.

   The contents of this object are identical in encoding to the contents
   of the Route Record Object defined in [RFC3209], [RFC3473] and
   [RFC3477].  That is, the object is constructed from a series of sub-
   objects.  Any RSVP RRO sub-object already defined or that could be
   defined in the future for use in the RRO is acceptable in this
   object.

   The meanings of all of the sub-objects and fields in this object are
   identical to those defined for the RRO.

   PCEP RRO sub-object types correspond to RSVP RRO sub-object types.

   RRO Object-Class is to be assigned by IANA (recommended value=8)

   RRO Object-Type is to be assigned by IANA (recommended value=1)

7.10.  LSPA Object

   The LSPA object is optional and specifies various TE LSP attributes
   to be taken into account by the PCE during path computation.  The
   LSPA (LSP Attributes) object can either be carried within a PCReq
   message or a PCRep message in case of unsuccessful path computation
   (in this case, the PCRep message also comprises a NO-PATH object and
   the LSPA object is used to indicate the set of constraint(s) that
   could not be satisfied).  Most of the fields of the LSPA object are
   identical to the fields of the SESSION-ATTRIBUTE object defined in



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   [RFC3209] and [RFC4090].  When absent from the PCReq message, this
   means that the Setup and Holding priorities are equal to 0, and there
   are no affinity constraints.

   LSPA Object-Class is to be assigned by IANA (recommended value=9)

   Two Objects-Types are defined for the LSPA object: LSPA without
   resource affinity (Object-Type to be assigned by IANA with
   recommended value=1) and LSPA with resource affinity (Object-type=2).

   The format of the LSPA object body with and without resource affinity
   are 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Setup Prio   |  Holding Prio |  Flags      |L|    Reserved   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   //                     Optional TLV(s)                         //
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    Figure 16: LSPA object body format (without resource affinity)

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Exclude-any                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Include-any                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Include-all                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Setup Prio   |  Holding Prio |  Flags  |L|     Reserved      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   //                     Optional TLV(s)                         //
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Figure 17: LSPA object body format (with resource affinity)

   Setup Prio (Setup Priority - 8 bits).  The priority of the session
   with respect to taking resources, in the range of 0 to 7.  The value
   0 is the highest priority.  The Setup Priority is used in deciding
   whether this session can preempt another session.

   Holding Prio (Holding Priority - 8 bits).  The priority of the



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   session with respect to holding resources, in the range of 0 to 7.
   The value 0 is the highest priority.  Holding Priority is used in
   deciding whether this session can be preempted by another session.
   Flags

   The flag L corresponds to the "Local protection desired" bit
   ([RFC3209]) of the SESSION-ATTRIBUTE Object.

   L Flag (Local protection desired).  When set, this means that the
   computed path must include links protected with Fast Reroute as
   defined in [RFC4090].

7.11.  IRO Object

   The IRO (Include Route Object) object is optional and can be used to
   specify that the computed path must traverse a set of specified
   network elements.  The IRO object may be carried within PCReq and
   PCRep messages.  When carried within a PCRep message with the NO-PATH
   object, the IRO indicates the set of elements that could not be
   included.

   IRO Object-Class is to be assigned by IANA (recommended value=10)

   IRO Object-Type is to be assigned by IANA (recommended value=1)

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   //                        (Subobjects)                         //
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                    Figure 18: IRO object body format
   Subobjects The IRO object is made of sub-object(s) identical to the
   ones defined in [RFC3209], [RFC3473] and [RFC3477] for use in EROs.

   The following subobject types are supported.

   Type   Subobject
        1   IPv4 prefix
        2   IPv6 prefix
        4   Unnumbered Interface ID
       32   Autonomous system number
   The L bit of such sub-object has no meaning within an IRO object.






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7.12.  SVEC Object

7.12.1.  Independent versus synchronized path computation requests

   The PCEP protocol allows for the bundling of multiple independent
   path computation requests within a single PCRep message.  A set of
   path computation requests is said to be non synchronized if their
   respective treatment (path computations) can be performed by a PCE in
   a serialized and independent fashion.

   There are various circumstances where the synchronization of a set of
   path computations may be beneficial or required.

   Consider the case of a set of N TE LSPs for which a PCC needs to send
   path computation requests to a PCE.  The first solution consists of
   sending N separate PCReq messages to the selected PCE.  In this case,
   the path computation requests are independent.  Note that the PCC may
   chose to distribute the set of N requests across K PCEs for load
   balancing reasons.  Considering that M (with M<N) requests are sent
   to a particular PCEi, as described above, such M requests can be sent
   in the form of successive PCReq messages destined to PCEi or grouped
   within a single PCReq message.  This is of course a viable solution
   if and only if such requests are independent.  That said, it can be
   desirable to request from the PCE the computation of their paths in a
   synchronized fashion that is likely to lead to more optimal path
   computations and/or reduced blocking probability if the PCE is a
   stateless PCE.  In other words, the PCE should not compute the
   corresponding paths in a serialized and independent manner but it
   should rather simultaneously compute their paths.

   For example, trying to simultaneously compute the paths of M TE LSPs
   may allow the PCE to improve the likelihood to meet multiple
   constraints.  Consider the case of two TE LSPs requesting N1 MBits/s
   and N2 MBits/s respectively and a maximum tolerable end-to-end delay
   for each TE LSP of X ms.  There may be circumstances where the
   computation of the first TE LSP irrespectively of the second TE LSP
   may lead to the impossibility to meet the delay criteria for the
   second TE LSP.  A second example is related to the bandwidth
   constraint.  It is quite straightforward to provide examples where a
   serialized independent path computation approach would lead to the
   impossibility to satisfy both requests (due to bandwidth
   fragmentation) while a synchronized path computation would
   successfully satisfy both requests.  A last example relates to the
   ability to avoid the allocation of the same resource to multiple
   requests thus helping to reduce the call set up failure probability
   compared to the serialized computation of independent requests.

   Furthermore, if the PCC has to send a large number of path



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   computation requests, it may also be desirable to pack multiple
   requests within a single PCReq object so as to minimize the control
   plane overhead.  Note that the algorithm used by the PCC to "pack" a
   set of requests introduces some unavoidable trade-off between control
   plane load and delays and such algorithm is outside of the scope of
   this document.

   There are other cases where the computation of M requests must be
   synchronized an obvious example of which being the computation of M
   diverse paths.  If such paths are computed in a non-synchronized
   fashion this seriously increases the probability of not being able to
   satisfy all requests (sometimes also referred to as the well-know
   "trapping problem").  Furthermore, this would not allow a PCE to
   implement objective functions such as trying to minimize the sum of
   the TE LSP costs.  In such a case, the path computation requests must
   be synchronized: they cannot be computed independently of each other.

   The synchronization of a set of path computation requests is achieved
   by using the SVEC object that specifies the list of synchronized
   requests along with the nature of the synchronization.

7.12.2.  SVEC Object

   Section 7.12.1 details the circumstances under which it may be
   desirable and/or required to synchronize a set of path computation
   requests.  The SVEC (Synchronization VECtor) object allows a PCC to
   request such synchronization.  The SVEC object is optional and may be
   carried within a PCReq message.

   The aim of the SVEC object carried within a PCReq message is to
   specify the correlation of M path computation requests.  The SVEC
   object is a variable length object that lists the set of M path
   computation requests that must be synchronized.  Each path
   computation request is uniquely identified by the Request-ID-number
   carried within the respective RP object.  The SVEC object also
   contains a set of flags that specify the synchronization type.

   SVEC Object-Class is to be assigned by IANA (recommended value=11)

   SVEC Object-Type is to be assigned by IANA (recommended value=1)

   One Object-Type is defined for this object to be assigned by IANA
   with a recommended value of 1.








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   The format of the SVEC 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Reserved    |                   Flags                 |S|N|L|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Request-ID-number #1                      |                                                               |
   //                                                             //
   |                     Request-ID-number #M                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                     Figure 19: SVEC body object format
   Flags: Defines the synchronization type between multiple path
   computation requests.

   L (Link diverse) bit: when set, this indicates that the computed
   paths corresponding to the requests specified by the following RP
   objects MUST not have any link in common.

   N (Node diverse) bit: when set, this indicates that the computed
   paths corresponding to the requests specified by the following RP
   objects MUST not have any node in common.

   S (SRLG diverse) bit: when set, this indicates that the computed
   paths corresponding to the requests specified by the following RP
   objects MUST not share any SRLG (Shared Risk Link Group).

   The flags defined above are not exclusive.

7.12.3.  Handling of the SVEC Object

   The SVEC object allows a PCC to specify a list of M path computation
   requests that must be synchronized along with the nature of the
   synchronization.  The set of M path computation requests may be sent
   within a single PCReq message or multiple PCReq message.  In the
   later case, it is RECOMMENDED for the PCE to implement a local timer
   upon the receipt of the first PCReq message that comprises the SVEC
   object after the expiration of which, if all the M path computation
   requests have not been received, a protocol error is triggered (this
   timer is called the SyncTimer).  In this case the PCE MUST cancel the
   whole set of path computation requests and MUST send a PCErr message
   with Error-Type="Synchronized path computation request missing".

   Note that such PCReq message may also comprise non-synchronized path
   computation requests.  For example, the PCReq message may comprise N
   synchronized path computation requests related to RP 1, ... , RP N
   listed in the SVEC object along with any other path computation
   requests.



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7.13.  NOTIFICATION Object

   The NOTIFICATION object is exclusively carried within a PCNtf message
   and can either be used in a message sent by a PCC to a PCE or by a
   PCE to a PCC so as to notify of an event.

   NOTIFICATION Object-Class is to be assigned by IANA (recommended
   value=12)

   NOTIFICATION Object-Type is to be assigned by IANA (recommended
   value=1)

   One Object-Type is defined for this object to be assigned by IANA
   with a recommended value of 1.

   The format of the NOTIFICATION body object 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Reserved    |     Flags     |      NT       |     NV        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   //                      Optional TLV(s)                         //
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

               Figure 20: NOTIFICATION body object format
   NT (Notification Type - 8 bits): the Notification-type specifies the
   class of notification

   NV (Notification Value - 8 bits): the Notification-value provides
   addition information related to the nature of the notification.

   Flags: no flags are currently defined.

   Both the Notification-type and Notification-value should be managed
   by IANA.

   The following Notification-type and Notification-value values are
   currently defined:

   o  Notification-type=1: Pending Request cancelled

      *  Notification-value=1: PCC cancels a set of pending request(s).
         A Notification-type=1, Notification-value=1 indicates that the
         PCC wants to inform a PCE of the cancellation of a set of
         pending request(s).  Such event could be triggered because of
         external conditions such as the receipt of a positive reply



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         from another PCE (should the PCC have sent multiple requests to
         a set of PCEs for the same path computation request), a network
         event such as a network failure rendering the request obsolete
         or any other event(s) local to the PCC.  A NOTIFICATION object
         with Notification-type=1, Notification-value=1 is exclusively
         carried within a PCNtf message sent by the PCC to the PCE.  The
         RP object MUST also be present in the PCNtf message.  Multiple
         RP objects may be carried within the PCNtf message in which
         case the notification applies to all of them.  If such
         notification is received by a PCC from a PCE, the PCC MUST
         silently ignore the notification and no errors should be
         generated.

      *  Notification-value=2: PCE cancels a set of pending request(s).
         A Notification-type=1, Notification-value=2 indicates that the
         PCE wants to inform a PCC of the cancellation of a set of
         pending request(s).  Such event could be triggered because of
         some PCE congested state or because of some path computation
         requests that are part the set of synchronized path computation
         requests are missing.  A NOTIFICATION object with Notification-
         type=1, Notification-value=2 is exclusively carried within a
         PCNtf message sent by a PCE to a PCC.  The RP object MUST also
         be present in the PCNtf message.  Multiple RP objects may be
         comprised within the PCNtf message in which case the
         notification applies to all of them.  If such notification is
         received by a PCE from a PCC, the PCE MUST silently ignore the
         notification and no errors should be generated.

   o  Notification-type=2: PCE congestion

      *  Notification-value=1.  A Notification-type=2, Notification-
         value=1 indicates to the PCC(s) that the PCE is currently in a
         congested state.  If no RP objects are comprised in the PCNtf
         message, this indicates that no other requests SHOULD be sent
         to that PCE until the congested state is cleared: the pending
         requests are not affected and will be served.  If some pending
         requests cannot be served due to the congested state, the PCE
         MUST also include a set of RP object(s) that identifies the set
         of pending requests that are now cancelled by the PCE and will
         not be honored.  In this case, the PCE does not have to send an
         additional PCNtf message with Notification-type=1 and
         Notification-value=2 since the list of cancelled requests is
         specified by including the corresponding set of RP object(s).
         If such notification is received by a PCE from a PCC, the PCE
         MUST silently ignore the notification and no errors should be
         generated.





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   Optionally, a TLV named CONGESTION-DURATION may be included in the
   NOTIFICATION object that specifies the duration during which no further
   request should be sent to the PCE. Once this period has expired the PCE
    should no longer be considered in congested state.

   The CONGESTION-DURATION TLV is composed of 1 octet for the type,
   1 octet specifying the number of bytes in the value field, 2 octets
   for an "Unused" field (the value of which MUST be set to 0), followed by
   a fix length value field of 4 octets specifying the estimated PCE
   congestion duration in seconds. The CONGESTION-DURATION TLV is padded
   to eight-octet alignment.

   TYPE: To be assigned by IANA
   LENGTH: 4
   VALUE: estimated congestion duration in seconds

      *  If a new PCEP session is established while the PCE is in
         congested state, the PCE MUST immediately send a PCErr with
         Notification-type=2, Notification-value=1 along with optionally
         the CONGESTION-DURATION TLV.

      *  Notification-value=2.  A Notification-type=2, Notification-
         value=2 indicates that the PCE is no longer in congested state
         and is available to process new path computation requests.  An
         implementation MUST make sure that a PCE sends such
         notification to every PCC to which a Notification message (with
         Notification-type=2, Notification-value=1) has been sent unless
         a CONGESTION-DURATION TLV has been included in the
         corresponding message and the PCE wishes to wait for the
         expiration of that period of time before receiving new
         requests.  An implementation may decide to cancel such
         notification if the PCC is in down state for a specific period.
         A RECOMMENDED value for such delay is 1 hour.  If such
         notification is received by a PCE from a PCC, the PCE MUST
         silently ignore the notification and no errors should be
         generated.  It is RECOMMENDED to support some dampening
         notification procedure on the PCE so as to avoid too frequent
         congestion notifications and releases.  For example, an
         implementation could make use of an hysteresis approach using a
         dual-thresholds mechanism triggering the sending of congestion
         notifications and releases.  Furthermore, in case of high
         instabilities of the PCE resources, an additional dampening
         mechanism SHOULD be used (linear or exponential) to pace the
         notification frequency and avoid path computation requests
         oscillation.






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7.14.  PCEP-ERROR Object

   The PCEP-ERROR object is exclusively carried within a PCErr message
   to notify of a PCEP protocol error.

   PCEP-ERROR Object-Class is to be assigned by IANA (recommended
   value=13)

   PCEP-ERROR Object-Type is to be assigned by IANA (recommended
   value=1)

   One Object-Type is defined for this object to be assigned by IANA
   with a recommended value of 1.

   The format of the PCEP-ERROR 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Reserved    |      Flags    |   Error-Type  |  Error-Value  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   //                     Optional TLV(s)                         //
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

               Figure 21: PCEP-ERROR object body format
   A PCEP-ERROR object is used to report a PCEP protocol error and is
   characterized by an Error-Type that 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 should be managed by
   IANA (see the IANA section).

   Flags (8 bits): no flag is currently defined.

   Error-type (8 bits): defines the class of error.

   Error-value (8 bits): provides additional details about the error.

   Optionally the PCEP-ERROR object may contain additional TLV so as to
   provide further information about the encountered error.  No TLV is
   currently defined.

   A single PCErr message may contain multiple PCEP-ERROR objects.








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   For each PCEP protocol error, an Error-type and an Error-value are
   defined.
   Error-Type    Meaning
      1          Capability not supported
      2          Unknown Object
                  Error-value=1: Unrecognized object class
                  Error-value=2: Unrecognized object Type
      3          Not supported object
                  Error-value=1: Not supported object class
                  Error-value=2: Not supported object Type
      4          Policy violation
                  Error-value=1: C bit of the METRIC object set (request rejected)
                  Error-value=2: O bit of the RP object set (request rejected)
      5          Mandatory Object missing
                  Error-value=1: RP object missing
                  Error-value=2: RRO object missing for a reoptimization
                                 request (R bit of the RP object set)
                  Error-value=3: END-POINTS object missing
      6          Synchronized path computation request missing
      7          Unknown request reference
      8          Unacceptable PCEP session characteristics
                  Error-value=1: parameter negotiation
                  Error-value=2: parameters negotiation failed
      9         Deadtimer expired

   Error-Type=1: the PCE indicates that the path computation request
   cannot be completed because it does not support one or more required
   capability.  The corresponding path computation request MUST be
   cancelled.

   Error-Type=2 or Error-Type=3: if a PCEP message is received that
   carries a PCEP object (with the P flag set) not recognized by the PCE
   or recognized but not supported, then the PCE MUST send a PCErr
   message with a PCEP-ERROR object (Error-Type=2 and 3 respectively).
   The corresponding path computation request MUST be cancelled by the
   PCE without further notification.

   Error-Type=4: if a path computation request is received which is not
   compliant with an agreed policy between the PCC and the PCE, the PCE
   MUST send a PCErr message with a PCEP-ERROR object (Error-Type=4).
   The corresponding path computation MUST be cancelled.  Policy-
   specific TLV(s) carried within the PCEP-ERROR object may be defined
   in other documents to specify the nature of the policy violation.

   Error-Type=5: if a path computation request is received that does not
   contain a mandatory object, the PCE MUST send a PCErr message with a
   PCEP-ERROR object (Error-Type=5).  If there are multiple mandatory
   objects missing, the PCErr message MUST contain one PCEP-ERROR object



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   per missing object.  The corresponding path computation MUST be
   cancelled.

   Error-Type=6: if a PCC sends a synchronized path computation request
   to a PCE and the PCE does not receive all the synchronized path
   computation requests listed within the corresponding SVEC object
   after the expiration of the timer SyncTimer defined in
   Section 7.12.3, the PCE MUST send a PCErr message with a PCEP-ERROR
   object (Error-Type=6).  The corresponding synchronized path
   computation MUST be cancelled.  It is RECOMMENDED for the PCE to
   include the REQ-MISSING TLV(s) (defined below) that identifies the
   missing request(s).

   The REQ-MISSING TLV is composed of 1 octet for the type,
   1 octet specifying the number of bytes in the value field, 2 octets
   for an "Unused" field (the value of which MUST be set to 0), followed by
   a fix length value field of 4 octets specifying the request-id-number
   that correspond to the missing request. The REQ-MISSING TLV is padded
   to eight-octet alignment.

   TYPE: To be assigned by IANA
   LENGTH: 4
   VALUE: request-id-number that corresponds to the missing request

   Error-Type=7: if a PCC receives a PCRep message related to an unknown
   path computation request, the PCC MUST send a PCErr message with a
   PCEP-ERROR object (Error-Type=7).  In addition, the PCC MUST include
   in the PCErr message the unknown RP object.

   Error-Type=8: if one or more PCEP session characteristic(s) are not
   acceptable by the receiving peer and are not negotiable, it MUST send
   a PCErr message with Error-type=8, Error-value=1.  Conditions under
   which such error message is sent are detailed in Section 6.2

   Error-Type=9: If a PCEP peer does not receive any PCEP message
   (Keepalive, PCReq, PCRep, PCNtf) during the Deadtimer period, the
   PCEP peer MUST send a PCErr message with a PCEP-ERROR object (Error-
   type=9, Error-value=1).  The PCEP session MUST be terminated
   according to the procedure defined in Section 6.8.

7.15.  CLOSE Object

   The CLOSE object MUST be present in each Close message.  There MUST
   be only one CLOSE object per Close message.

   CLOSE Object-Class is to be assigned by IANA (recommended value=14)

   CLOSE Object-Type is to be assigned by IANA (recommended value=1)



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   The format of the CLOSE 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Reserved             |      Flags    |    Reason     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   //                         Optional TLV(s)                     //
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                    Figure 14: CLOSE Object format
   Reason (4 bits): specifies the reason for closing the PCEP session.
   The setting of this field is optional.  Two values are currently
   defined.

   Reasons
    Value        Meaning
      1          No explanation provided
      2          DeadTimer expired
      3          PCEP session characteristics negotiation failure
   Flags (4 bits): No Flags are currently defined.

   Optional TLVs may be included within the CLOSE object body.  The
   specification of such TLVs is outside the scope of this document.


8.  Manageability Considerations

   It is expected and required to specify a MIB for the PCEP
   communication protocol (in a separate document).  Furthermore,
   additional tools related to performance, fault and diagnostic
   detection are required which will also be specified in separate
   documents.


9.  IANA Considerations

9.1.  TCP Port

   The PCEP protocol will use a well-known TCP port to be assigned by
   IANA.

9.2.  PCEP Messages

   Each PCEP message has a Message-Type.





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   Value    Meaning
     1        Open
     2        Keepalive
     3        Path Computation Request
     4        Path Computation Reply
     5        Notification
     6        Error
     7        Close

9.3.  PCEP Object

   IANA assigns value to PCEP parameters.  Each PCEP object has an
   Object-Class and an Object-Type.

   Object-Class      Name

          1                 OPEN
                            Object-Type
                               1

          2                 RP
                            Object-Type
                               1

          3                 NO-PATH
                            Object-Type
                               1

          4                 END-POINTS
                            Object-Type
                               1 : IPv4 addresses
                               2: IPv6 addresses

          5                 BANDWIDTH
                            Object-Type
                               1: Requested bandwidth
                               2: Bandwidth of an existing TE LSP
                                  for which a reoptimization is performed.

          6                 METRIC
                            Object-Type
                               1

          7                 ERO
                            Object-Type
                               1

          8                 RRO



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                            Object-Type
                               1

          9                 LSPA
                            Object-Type
                               1: without resource affinity
                               2: with resource affinity

         10                 IRO
                            Object-Type
                               1

         11                 SVEC
                            Object-Type
                               1

         12                 NOTIFICATION
                            Object-Type
                               1

         13                 PCEP-ERROR
                            Object-Type
                               1

         14                 CLOSE
                            Object-Type
                               1

9.4.  Notification

   A NOTIFICATION object is characterized by a Notification-type that
   specifies the class of notification and a Notification-value that
   provides additional information related to the nature of the
   notification.  Both the Notification-type and Notification-value are
   managed by IANA (see IANA section).
















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   Notification-type     Name
            1                    Pending Request cancelled
                                  Notification-value
                                           1: PCC cancels a set of pending request(s)
                                           2: PCE cancels a set of pending request(s)
            2                    PCE Congestion
                                  Notification-value
                                           1: PCE in congested state
                                           2: PCE no longer in congested state

9.5.  PCEP Error

   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.



































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   Error-type          Meaning
         1                  Capability not supported
                             Error-value
                                   1

         2                  Unknown Object
                             Error-value
                                   1: Unrecognized object class
                                   2: Unrecognized object Type

         3                  Not supported object
                             Error-value
                                   1: Not supported object class
                                   2: Not supported object Type

         4                  Policy violation
                             Error-value
                                   1: C bit of the METRIC object set (request rejected)
                                   2: O bit of the RP object set (request rejected)

         5                  Mandatory object missing
                             Error-value
                                   1: RP object missing
                                   2: RRO object missing for a reoptimization request
                                      (R bit of the RP object set)
                                   3: END-POINTS object missing

         6                  Synchronized path computation request missing
                             Error-value
                                   1

         7                  Unknown request reference
                             Error-value
                                   1

         8                  Unacceptable PCEP session characteristics
                             Error-value
                                  1

         9                  Deadtimer expiration
                             Error-value
                                  1


10.  PCEP Finite State Machine (FSM)

   The section describes the PCEP Finite State Machine (FSM).




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   PCEP Finite State Machine


          +-+-+-+-+-+-+<------+
   +------| SessionUP |<---+  |
   |      +-+-+-+-+-+-+    |  |
   |                       |  |
   |   +->+-+-+-+-+-+-+    |  |
   |   |  | KeepWait  |----+  |
   |   +--|           |<---+  |
   |+-----+-+-+-+-+-+-+    |  |
   ||          |           |  |
   ||          |           |  |
   ||          V           |  |
   ||  +->+-+-+-+-+-+-+----+  |
   ||  |  | OpenWait  |-------+
   ||  +--|           |<------+
   ||+----+-+-+-+-+-+-+<---+  |
   |||         |           |  |
   |||         |           |  |
   |||         V           |  |
   ||| +->+-+-+-+-+-+-+    |  |
   ||| |  |TCPPending |----+  |
   ||| +--|           |       |
   |||+---+-+-+-+-+-+-+<---+  |
   ||||        |           |  |
   ||||        |           |  |
   ||||        V           |  |
   |||+--->+-+-+-+-+       |  |
   ||+---->| Idle  |-------+  |
   |+----->|       |----------+
   +------>+-+-+-+-+

   Figure 15: PCEP Finite State Machine for the PCC

   PCEP defines the following set of variables:

   TCPConnect: timer (in seconds) started after having initialized a TCP
   connection using the PCEP well-known TCP port.  The value of the
   TCPConnect timer is 60 seconds.  TCPRetry: specifies the number of
   times the system has tried to establish a TCP connection with a PCEP
   peer without success.  TCPMaxRetry: Maximum number of times the
   system tries to establish a TCP connection using the PCEP well-known
   TCP port before going back to the Idle state.  The value of the
   TCPMaxRetry is 5.  OpenWait: timer (in seconds) that corresponds to
   the amount of time a PCEP peer will wait to receive an Open message
   from the PCEP peer after the expiration of which the system releases
   the PCEP resource and go back to the Idle state.  KeepWait: timer (in



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   seconds) that corresponds to the amount of time a PCEP peer will wait
   to receive a KeepAlive or a PCErr message from the PCEP peer after
   the expiration of which the system releases the PCEP resource and go
   back to the Idle state.  OpenRetry: specifies the number of times the
   system has received an Open message with unacceptable PCEP session
   characteristics.  OpenMaxRetry: Maximum number of times the system
   can receive an Open message with unacceptable PCEP sessions
   characteristics before releasing the PCEP session with that peer and
   go back to Idle state.  The value of the OpenMaxRetry is 3.  The
   following two states variable are defined:

   RemoteOK: the RemoteOK variable is a Boolean set to 1 if the system
   has received an acceptable Open message.  LocalOK: the LocalOK
   variable is a Boolean set to 1 if the system has received a Keepalive
   message acknowledging that the Open message sent to the peer was
   valid.

   Idle State:

   The idle state is the initial PCEP state where PCEP (also referred to
   as "the system") waits for an initialization event that can either be
   manually triggered by the user (configuration) or automatically
   triggered by various events.  In Idle state, PCEP resources are
   allocated (memory, potential process, ...) but no PCEP messages are
   accepted from any PCEP peer.  The system listens the well-known PCEP
   TCP port.

   The following set of variable are initialized:

   TCPRetry=0,

   LocalOK=0,

   RemoteOK=0,

   Upon detection of a local initialization event (e.g. user
   configuration to establish a PCEP session with a particular PCEP
   peer, local event triggering the establishment of a PCEP session with
   a PCEP peer, ...), the system:

   o  Starts the TCPConnect timer,

   o  Initiates of a TCP connection with the PCEP peer,

   o  Increments the TCPRetry variable,

   o  Moves to the TCPPending state.




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   Upon receiving a TCP connection on the well-known PCEP TCP port, if
   the TCP connection establishment succeeds, the system:

   o  Sends an Open message

   o  Starts the OpenWait timer

   o  Moves to the OpenWait state

   It is expected that an implementation will use an exponentially
   increase timer between automatically generated Initialization events
   and between retrials of TCP connection establishments.

   TCPPending State

   If the TCP connection establishment succeeds, the system:

   o  Sends an Open message,

   o  Starts the OpenWait timer,

   o  Starts the KeepWait timer,

   o  Moves to the OpenWait state.

   If the TCP connection establishement fails (an error is detected
   during the TCP connection establishment) or the TCPConnectTimer
   expires:

   If TCPRetry =TCPMaxRetry the system moves to the Idle State

   If TCPRetry variable < TCPMaxRetry the system:

   o  Starts the TCPConnect timer,

   o  Initiates of a TCP connection with the PCEP peer,

   o  Increments the TCPRetry variable.

   If the system detects that the PCEP peer tries to simultaneously
   establish a TCP connection, it stops the TCP connection establishment
   if and only if the PCEP peer has a higher IP address and moves to the
   Idle state.  This guarantees that in case of "collision" a single TCP
   connection is established.

   OpenWait State:

   In the OpenWait state, the system waits for an Open message from its



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   PCEP peer.

   If the system receives an Open message from the PCEP peer before the
   expiration of the OpenWait timer, PCEP checks the PCEP session
   attributes (Keepalive frequency, DeadTimer, ...).

   If an error is detected (malformed Open message, unsupported PCEP
   session characteristics), PCEP generates an error notification,
   release the PCEP resources for the PCEP peer, closes the TCP
   connection and moves to the Idle state.

   If no Open message is received before the expiration of the OpenWait
   timer, the system releases the PCEP resources for the PCEP peer,
   closes the TCP connection and moves to the Idle state.

   If no errors are detected and the session characteristics are
   acceptable to the local system, the system:

   o  Sends a Keepalive message to the PCEP peer,

   o  Starts the Keepalive timer,

   o  Sets the RemoteOK variable to 1.

   If LocalOK=1 the system moves to the UP state

   If LocalOK=0 the system moves to the KeepWait state.

   If no errors are detected but there is a disagreement on the session
   characteristics (such as the Keepalive frequency or the DeadTimer), a
   PCErr message is sent to the peer (reporting the values for which a
   disagreement exists).

   If OpenRetry=OpenMaxRetry the system releases the PCEP resources for
   that peer amd moves back to the Idle state.

   If OpenRetry < OpenMaxRetry the system:

   o  sends a PCErr message containing proposed acceptable session
      characteristics,

   o  Increments the OpenRetry variable.

   KeepWait State

   In the Keepwait state, the system waits for the receipt of a
   Keepalive from its PCEP peer acknowledging its Open message or a
   PCErr message in response to unacceptable PCEP session



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   characteristics proposed in the Open message.

   If a Keepalive message is received before the expiration of the
   KeepWait timer, LocalOK=1

   If RemoteOK=1, the system moves to the UP state.

   If RemoteOK=0, the system moves to the OpenWait State.

   If a PCErr message is received before the expiration of the KeepWait
   timer:

   1.  If the proposed values are unacceptable, the sytem releases the
       PCEP resources for that PCEP peer, closes the TCP connection and
       moves to the Idle state.

   2.  If the proposed values are acceptable, the sytem adjusts its PCEP
       session characteristics according to the proposed values received
       in the PCErr message restarts the KeepWait timer and sends a new
       Open message.  If RemoteOK=1, the system stays in the KeepWait
       state.  If RemoteOK=0, the system moves to the OpenWait state.

   If neither a Keepalive nor a PCErr is received after the expiration
   of the KeepWait timer, the system releases the PCEP resources for
   that PCEP peer, closes the TCP connection and moves to the Idle
   State.

   UP State

   In the UP state, the PCEP peer starts exchanging PCEP messages
   according to the session characteristics.

   If the Keepalive timer expires, the systens sends a Keepalive
   message.

   If no Keepalive message is received from the PCEP peer after the
   expiration of the DeadTimer, the systems sends a PCEP CLOSE message,
   releases the PCEP resources for that PCEP peer, closes the TCP
   connection and moves to the Idle State.

   In a malformed PCEP message is received or the TCP connection fails,
   the systems sends a PCEP CLOSE message, the system releases the PCEP
   resources for that PCEP peer, closes the TCP connection and moves to
   the Idle State.


11.  Security Considerations




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   The PCEP protocol could be the target of the following attacks:

   o  Spoofing (PCC or PCE impersonation)

   o  Snooping (message interception)

   o  Falsification

   o  Denial of Service

   A PCEP attack may have significant impact, particularly in an
   inter-AS context as PCEP facilitates inter-AS path establishment.
   Several mechanisms are proposed below, so as to ensure
   authentication, integrity and privacy of PCEP Communications, and
   also to protect against DoS attacks.

11.1.  PCEP Authentication and Integrity

   It is RECOMMENDED to use TCP-MD5 [RFC1321] signature option to
   provide for the authenticity and integrity of PCEP messages.  This
   will allow protecting against PCE or PCC impersonation and also
   against message content falsification.

   This requires the maintenance, exchange and configuration of MD-5
   keys on PCCs and PCEs.  Note that such maintenance may be especially
   onerous to the operators as pointed out in [I-D.ietf-rpsec-
   bgpsecrec].  Hence it is important to limit the number of keys while
   ensuring the required level of security.

   MD-5 signature faces some limitations, as per explained in [RFC2385].
   Note that when one digest technique stronger than MD5 is specified
   and implemented, PCEP could be easily upgraded to use it.

11.2.  PCEP Privacy

   Ensuring PCEP communication privacy is of key importance, especially
   in an inter-AS context, where PCEP communication end-points do not
   reside in the same AS, as an attacker that intercept a PCE message
   could obtain sensitive information related to computed paths and
   resources.  Privacy can be ensured thanks to encryption.  To ensure
   privacy of PCEP communication, IPSec [RFC2406] tunnels MAY be used
   between PCC and PCEs or between PCEs.  Note that this could also be
   used to ensure Authentication and Integrity, in which case, TCP MD-5
   option would not be required.

11.3.  Protection against Denial of Service attacks

   PCEP can be the target of TCP DoS attacks, such as for instance SYN



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   attacks, as all protocols running on top of TCP.  PCEP can use the
   same mechanisms as defined in [RFC3036] to mitigate the threat of
   such attacks:

   o  A PCE should avoid promiscuous TCP listens for PCEP TCP session
      establishment.  It should use only listens that are specific to
      authorized PCCs.

   o  The use of the MD5 option helps somewhat since it prevents a SYN
      from being accepted unless the MD5 segment checksum is valid.
      However, the receiver must compute the checksum before it can
      decide to discard an otherwise acceptable SYN segment.

   o  The use of access-list on the PCE so as to restrict access to
      authorized PCCs.

11.4.  Request input shaping/policing

   A PCEP implementation may be subject to Denial Of Service attacks
   consisting of sending a very large number of PCEP messages (e.g.
   PCReq messages).  Thus, especially in multi-Service Providers
   environments, a PCE implementation should implement request input
   shaping/policing so as to throttle the amount of received PCEP
   messages without compromising the implementation behavior.


12.  Acknowledgements

   The authors would like to thank Dave Oran, Dean Cheng, Jerry Ash,
   Igor Bryskin, Carol Iturrade, Siva Sivabalan, Rich Bradford, Richard
   Douville for their very valuable input.  Special thank to Adrian
   Farrel for his very valuable suggestions.


13.  References

13.1.  Normative References

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

   [RFC2205]  Braden, B., Zhang, L., Berson, S., Herzog, S., and S.
              Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1
              Functional Specification", RFC 2205, September 1997.

   [RFC3209]  Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
              and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
              Tunnels", RFC 3209, December 2001.



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   [RFC3473]  Berger, L., "Generalized Multi-Protocol Label Switching
              (GMPLS) Signaling Resource ReserVation Protocol-Traffic
              Engineering (RSVP-TE) Extensions", RFC 3473, January 2003.

   [RFC3477]  Kompella, K. and Y. Rekhter, "Signalling Unnumbered Links
              in Resource ReSerVation Protocol - Traffic Engineering
              (RSVP-TE)", RFC 3477, January 2003.

   [RFC4090]  Pan, P., Swallow, G., and A. Atlas, "Fast Reroute
              Extensions to RSVP-TE for LSP Tunnels", RFC 4090,
              May 2005.

13.2.  Informative References

   [I-D.ietf-ccamp-inter-domain-rsvp-te]
              Ayyangar, A. and J. Vasseur, "Inter domain GMPLS Traffic
              Engineering - RSVP-TE extensions",
              draft-ietf-ccamp-inter-domain-rsvp-te-03 (work in
              progress), March 2006.

   [I-D.ietf-pce-architecture]
              Farrel, A., "A Path Computation Element (PCE) Based
              Architecture", draft-ietf-pce-architecture-05 (work in
              progress), April 2006.

   [I-D.ietf-pce-comm-protocol-gen-reqs]
              Roux, J. and J. Ash, "PCE Communication Protocol Generic
              Requirements", draft-ietf-pce-comm-protocol-gen-reqs-06
              (work in progress), May 2006.

   [I-D.ietf-pce-disco-proto-igp]
              Roux, J., "IGP protocol extensions for Path Computation
              Element (PCE) Discovery",
              draft-ietf-pce-disco-proto-igp-01 (work in progress),
              March 2006.

   [I-D.ietf-pce-discovery-reqs]
              Roux, J., "Requirements for Path Computation Element (PCE)
              Discovery", draft-ietf-pce-discovery-reqs-05 (work in
              progress), June 2006.

   [I-D.ietf-pce-inter-layer-req]
              Oki, E., "PCC-PCE Communication Requirements for Inter-
              Layer Traffic Engineering",
              draft-ietf-pce-inter-layer-req-01 (work in progress),
              March 2006.

   [I-D.ietf-pce-pcecp-interarea-reqs]



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              Roux, J., "PCE Communication Protocol (PCECP) Specific
              Requirements for Inter-Area  (G)MPLS Traffic Engineering",
              draft-ietf-pce-pcecp-interarea-reqs-01 (work in progress),
              February 2006.

   [I-D.ietf-rpsec-bgpsecrec]
              Christian, B. and T. Tauber, "BGP Security Requirements",
              draft-ietf-rpsec-bgpsecrec-06 (work in progress),
              June 2006.

   [RFC1321]  Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321,
              April 1992.

   [RFC2385]  Heffernan, A., "Protection of BGP Sessions via the TCP MD5
              Signature Option", RFC 2385, August 1998.

   [RFC2406]  Kent, S. and R. Atkinson, "IP Encapsulating Security
              Payload (ESP)", RFC 2406, November 1998.

   [RFC3036]  Andersson, L., Doolan, P., Feldman, N., Fredette, A., and
              B. Thomas, "LDP Specification", RFC 3036, January 2001.

   [RFC3785]  Le Faucheur, F., Uppili, R., Vedrenne, A., Merckx, P., and
              T. Telkamp, "Use of Interior Gateway Protocol (IGP) Metric
              as a second MPLS Traffic Engineering (TE) Metric", BCP 87,
              RFC 3785, May 2004.

   [RFC4101]  Rescorla, E. and IAB, "Writing Protocol Models", RFC 4101,
              June 2005.


Appendix A.  Proposed Status and Discussion [To Be Removed Upon
             Publication]

   This Internet-Draft is being submitted for eventual publication as an
   RFC with a proposed status of Standard.  Discussion of this proposal
   should take place on the following mailing list: pce@ietf.org.


Appendix B.  Compliance with the PCECP Requirement Document

   The aim of this section is to list the set of requirements set forth
   in [I-D.ietf-pce-comm-protocol-gen-reqs] that are not satisfied by
   the current revision of this document.  This only concerns the
   requirements listed as MUST according to [RFC2119].

   Here is the list of currently unsatisfied requirements:




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   o  Allow to select/prefer from advertised list of standard objective
      functions/options

   o  Allow to customize objective function/options

   o  Allow indicating if load-balancing is allowed

   o  Support "unsynchronized" & "synchronized" objective functions

   o  Protocol recovery support resynchronization of information &
      requests between sender & receiver.


Appendix C.  PCEP Variables

   PCEP defines variable that can be configured.  The following PCEP
   variables are defined.

   KeepAlive timer: minimum period of time between the sending of PCEP
   messages (Keepalive, PCReq, PCRep, PCNtf) to a PCEP peer.  A
   suggested value for the Keepalive timer is 30 seconds.

   DeadTimer: period of timer after the expiration of which a PCEP peer
   declared the session down if no PCEP message has been received.

   SyncTimer: the SYNC timer is used in the case of synchronized path
   computation request using the SVEC object defined in Section 7.12.3.
   Consider the case where a PCReq message is received by a PCE that
   comprises the SVEC object referring to M synchronized path
   computation requests.  If after the expiration of the SYNC timer all
   the M path computation requests have not been received, a protocol
   error is triggered and the PCE MUST cancel the whole set of path
   computation requests.  A RECOMMENDED value for the SYNC timer is 60
   seconds.

















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Authors' Addresses

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

   Email: jpv@cisco.com


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

   Email: jeanlouis.leroux@francetelecom.com


   Arthi Ayyangar
   Juniper Networks
   1194 N.Mathilda Avenue
   Sunnyvale, CA  94089
   USA

   Email: arthi@juniper.net


   Eiji Oki
   NTT
   Midori 3-9-11
   Musashino, Tokyo,   180-8585
   JAPAN

   Email: oki.eiji@lab.ntt.co.jp


   Alia Atlas
   Google
   1600 Amphitheatre Parkway
   Montain View, CA  94043
   USA

   Email: akatlas@alum.mit.edu






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   Andrew Dolganow
   Alcatel
   600 March Road
   Ottawa, ON  K2K 2E6
   CANADA

   Email: andrew.dolganow@alcatel.com


   Yuichi Ikejiri
   NTT Communications Corporation
   1-1-6 Uchisaiwai-cho, Chiyoda-ku
   Tokyo,   100-819
   JAPAN

   Email: y.ikejiri@ntt.com


   Kenji Kumaki
   KDDI Corporation
   Garden Air Tower Iidabashi, Chiyoda-ku,
   Tokyo,   102-8460
   JAPAN

   Email: ke-kumaki@kddi.com


























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