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rfc:rfc5440

Network Working Group JP. Vasseur, Ed. Request for Comments: 5440 Cisco Systems Category: Standards Track JL. Le Roux, Ed.

                                                        France Telecom
                                                            March 2009
    Path Computation Element (PCE) Communication Protocol (PCEP)

Status of This Memo

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

Copyright Notice

 Copyright (c) 2009 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents in effect on the date of
 publication of this document (http://trustee.ietf.org/license-info).
 Please review these documents carefully, as they describe your rights
 and restrictions with respect to this document.
 This document may contain material from IETF Documents or IETF
 Contributions published or made publicly available before November
 10, 2008.  The person(s) controlling the copyright in some of this
 material may not have granted the IETF Trust the right to allow
 modifications of such material outside the IETF Standards Process.
 Without obtaining an adequate license from the person(s) controlling
 the copyright in such materials, this document may not be modified
 outside the IETF Standards Process, and derivative works of it may
 not be created outside the IETF Standards Process, except to format
 it for publication as an RFC or to translate it into languages other
 than English.

Vasseur & Le Roux Standards Track [Page 1] RFC 5440 PCEP March 2009

Abstract

 This document specifies the Path Computation Element (PCE)
 Communication Protocol (PCEP) for communications between a Path
 Computation Client (PCC) and a 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 Multiprotocol Label Switching (MPLS)
 and Generalized MPLS (GMPLS) Traffic Engineering.  PCEP 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.

Vasseur & Le Roux Standards Track [Page 2] RFC 5440 PCEP March 2009

Table of Contents

 1. Introduction ....................................................5
    1.1. Requirements Language ......................................5
 2. Terminology .....................................................5
 3. Assumptions .....................................................6
 4. Architectural Protocol Overview (Model) .........................7
    4.1. Problem ....................................................7
    4.2. Architectural Protocol Overview ............................7
         4.2.1. Initialization Phase ................................8
         4.2.2. Session Keepalive ...................................9
         4.2.3. Path Computation Request Sent by a PCC to a PCE ....10
         4.2.4. Path Computation Reply Sent by The PCE to a PCC ....11
         4.2.5. Notification .......................................12
         4.2.6. Error ..............................................14
         4.2.7. Termination of the PCEP Session ....................14
         4.2.8. Intermittent versus Permanent PCEP Session .........15
 5. Transport Protocol .............................................15
 6. PCEP Messages ..................................................15
    6.1. Common Header .............................................16
    6.2. Open Message ..............................................16
    6.3. Keepalive Message .........................................18
    6.4. Path Computation Request (PCReq) Message ..................19
    6.5. Path Computation Reply (PCRep) Message ....................20
    6.6. Notification (PCNtf) Message ..............................21
    6.7. Error (PCErr) Message .....................................22
    6.8. Close Message .............................................23
    6.9. Reception of Unknown Messages .............................23
 7. Object Formats .................................................23
    7.1. PCEP TLV Format ...........................................24
    7.2. Common Object Header ......................................24
    7.3. OPEN Object ...............................................25
    7.4. RP Object .................................................27
         7.4.1. Object Definition ..................................27
         7.4.2. Handling of the RP Object ..........................30
    7.5. NO-PATH Object ............................................31
    7.6. END-POINTS Object .........................................34
    7.7. BANDWIDTH Object ..........................................35
    7.8. METRIC Object .............................................36
    7.9. Explicit Route Object .....................................39
    7.10. Reported Route Object ....................................39
    7.11. LSPA Object ..............................................40
    7.12. Include Route Object .....................................42
    7.13. SVEC Object ..............................................42
         7.13.1. Notion of Dependent and Synchronized Path
                 Computation Requests ..............................42
         7.13.2. SVEC Object .......................................44
         7.13.3. Handling of the SVEC Object .......................45

Vasseur & Le Roux Standards Track [Page 3] RFC 5440 PCEP March 2009

    7.14. NOTIFICATION Object ......................................46
    7.15. PCEP-ERROR Object ........................................49
    7.16. LOAD-BALANCING Object ....................................54
    7.17. CLOSE Object .............................................55
 8. Manageability Considerations ...................................56
    8.1. Control of Function and Policy ............................56
    8.2. Information and Data Models ...............................57
    8.3. Liveness Detection and Monitoring .........................57
    8.4. Verifying Correct Operation ...............................58
    8.5. Requirements on Other Protocols and Functional
         Components ................................................58
    8.6. Impact on Network Operation ...............................58
 9. IANA Considerations ............................................59
    9.1. TCP Port ..................................................59
    9.2. PCEP Messages .............................................59
    9.3. PCEP Object ...............................................59
    9.4. PCEP Message Common Header ................................61
    9.5. Open Object Flag Field ....................................61
    9.6. RP Object .................................................61
    9.7. NO-PATH Object Flag Field .................................62
    9.8. METRIC Object .............................................63
    9.9. LSPA Object Flag Field ....................................63
    9.10. SVEC Object Flag Field ...................................64
    9.11. NOTIFICATION Object ......................................64
    9.12. PCEP-ERROR Object ........................................65
    9.13. LOAD-BALANCING Object Flag Field .........................67
    9.14. CLOSE Object .............................................67
    9.15. PCEP TLV Type Indicators .................................68
    9.16. NO-PATH-VECTOR TLV .......................................68
 10. Security Considerations .......................................69
    10.1. Vulnerability ............................................69
    10.2. TCP Security Techniques ..................................70
    10.3. PCEP Authentication and Integrity ........................70
    10.4. PCEP Privacy .............................................71
    10.5. Key Configuration and Exchange ...........................71
    10.6. Access Policy ............................................73
    10.7. Protection against Denial-of-Service Attacks .............73
         10.7.1. Protection against TCP DoS Attacks ................73
         10.7.2. Request Input Shaping/Policing ....................74
 11. Acknowledgments ...............................................75
 12. References ....................................................75
    12.1. Normative References .....................................75
    12.2. Informative References ...................................76
 Appendix A.  PCEP Finite State Machine (FSM) ......................79
 Appendix B.  PCEP Variables .......................................85
 Appendix C.  Contributors .........................................86

Vasseur & Le Roux Standards Track [Page 4] RFC 5440 PCEP March 2009

1. Introduction

 [RFC4655] describes the motivations and architecture for a Path
 Computation Element (PCE) based model for the computation of
 Multiprotocol Label Switching (MPLS) and Generalized MPLS (GMPLS)
 Traffic Engineering Label Switched Paths (TE LSPs).  The model allows
 for the separation of PCE from Path Computation Client (PCC), and
 allows for the cooperation between PCEs.  This necessitates a
 communication protocol between PCC and PCE, and between PCEs.
 [RFC4657] states the generic requirements for such a protocol
 including that the same protocol be used between PCC and PCE, and
 between PCEs.  Additional application-specific requirements (for
 scenarios such as inter-area, inter-AS, etc.) are not included in
 [RFC4657], 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 [RFC4927], [RFC5376],
 and [INTER-LAYER].
 This document specifies the Path Computation Element Protocol (PCEP)
 for communications between a PCC and a PCE, or between two PCEs, in
 compliance with [RFC4657].  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.
 PCEP 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.

1.1. 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].

2. Terminology

 The following terminology is used in this document.
 AS:  Autonomous System.
 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.

Vasseur & Le Roux Standards Track [Page 5] RFC 5440 PCEP March 2009

 Inter-domain TE LSP:  A TE LSP whose path transits at least two
    different domains where a domain can be an IGP area, an Autonomous
    System, or a sub-AS (BGP confederation).
 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 a
    PCE).
 TED:  Traffic Engineering Database that 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:  A mix of strict and loose hops comprising at
    least one loose hop representing the destination where a hop may
    be an abstract node such as an AS.
 Within this document, when describing PCE-PCE communications, the
 requesting PCE fills the role of a PCC.  This provides a saving in
 documentation without loss of function.
 The message formats in this document are specified using Backus-Naur
 Format (BNF) encoding as specified in [RBNF].

3. Assumptions

 [RFC4655] describes various types of PCE.  PCEP does not make any
 assumption about, and thus does not impose any constraint on, the
 nature of the PCE.
 Moreover, it is assumed that the PCE has the required information
 (usually including network topology and resource information) so as
 to perform the computation of a path for a TE LSP.  Such information
 can be gathered by routing protocols or by some other means.  The way
 in which the information is gathered is out of the scope of this
 document.
 Similarly, no assumption is made about the discovery method used by a
 PCC to discover a set of PCEs (e.g., via static configuration or
 dynamic discovery) and on the algorithm used to select a PCE.  For

Vasseur & Le Roux Standards Track [Page 6] RFC 5440 PCEP March 2009

 reference, [RFC4674] defines a list of requirements for dynamic PCE
 discovery and IGP-based solutions for such PCE discovery are
 specified in [RFC5088] and [RFC5089].

4. Architectural Protocol Overview (Model)

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

4.1. Problem

 The PCE-based architecture used for the computation of paths for MPLS
 and GMPLS TE LSPs is described in [RFC4655].  When the PCC and the
 PCE are not collocated, a communication protocol between the PCC and
 the PCE is needed.  PCEP is such a protocol designed specifically for
 communications between a PCC and a PCE or between two PCEs in
 compliance with [RFC4657]: a PCC may use PCEP to send a path
 computation request for one or more TE LSPs to a PCE, and the PCE may
 reply with a set of computed paths if one or more paths can be found
 that satisfies the set of constraints.

4.2. Architectural Protocol Overview

 PCEP operates over TCP, which fulfills the requirements for reliable
 messaging and flow control without further protocol work.
 Several PCEP messages are defined:
 o  Open and Keepalive messages are used to initiate and maintain a
    PCEP session, respectively.
 o  PCReq: a PCEP message sent by a PCC to a PCE to request a path
    computation.
 o  PCRep: a PCEP message sent by a PCE to a PCC in reply to a path
    computation request.  A PCRep message can contain either a set of
    computed paths if the request can be satisfied, or a negative
    reply if not.  The negative reply may indicate the reason why no
    path could be found.
 o  PCNtf: a PCEP notification message either sent by a PCC to a PCE
    or sent by a PCE to a PCC to notify of a specific event.
 o  PCErr: a PCEP message sent upon the occurrence of a protocol error
    condition.

Vasseur & Le Roux Standards Track [Page 7] RFC 5440 PCEP March 2009

 o  Close message: a message used to close a PCEP session.
 The set of available PCEs may be either statically configured on a
 PCC or dynamically discovered.  The mechanisms used to discover one
 or more PCEs and to select a PCE are 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.
 Each PCEP message is regarded as a single transmission unit and parts
 of messages MUST NOT be interleaved.  So, for example, a PCC sending
 a PCReq and wishing to close the session, must complete sending the
 request message before starting to send a Close message.

4.2.1. 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 PCEP session establishment
 during which various session parameters are negotiated.  These
 parameters are carried within Open messages and include the Keepalive
 timer, the DeadTimer, 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 session 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 an exponential back-off session establishment retry procedure.
 Keepalive messages are used to acknowledge Open messages, and are
 used once the PCEP session has been successfully established.
 Only one PCEP session can exist between a pair of PCEP peers at any
 one time.  Only one TCP connection on the PCEP port can exist between
 a pair of PCEP peers at any one time.
 Details about the Open message and the Keepalive message can be found
 in Sections 6.2 and 6.3, respectively.

Vasseur & Le Roux Standards Track [Page 8] RFC 5440 PCEP March 2009

             +-+-+                 +-+-+
             |PCC|                 |PCE|
             +-+-+                 +-+-+
               |                     |
               | Open msg            |
               |--------             |
               |        \   Open msg |
               |         \  ---------|
               |          \/         |
               |          /\         |
               |         /  -------->|
               |        /            |
               |<------     Keepalive|
               |             --------|
               |Keepalive   /        |
               |--------   /         |
               |        \/           |
               |        /\           |
               |<------   ---------->|
               |                     |
 Figure 1: PCEP Initialization Phase (Initiated by a PCC)
 (Note that once the PCEP session is established, the exchange of
 Keepalive messages is optional.)

4.2.2. Session Keepalive

 Once a session has been established, a PCE or PCC may want to know
 that its PCEP peer is still available for use.
 It can rely on TCP for this information, but it is possible that the
 remote PCEP function has failed without disturbing the TCP
 connection.  It is also possible to rely on the mechanisms built into
 the TCP implementations, but these might not provide failure
 notifications that are sufficiently timely.  Lastly, a PCC could wait
 until it has a path computation request to send and could use its
 failed transmission or the failure to receive a response as evidence
 that the session has failed, but this is clearly inefficient.
 In order to handle this situation, PCEP includes a keepalive
 mechanism based on a Keepalive timer, a DeadTimer, and a Keepalive
 message.
 Each end of a PCEP session runs a Keepalive timer.  It restarts the
 timer every time it sends a message on the session.  When the timer
 expires, it sends a Keepalive message.  Other traffic may serve as
 Keepalive (see Section 6.3).

Vasseur & Le Roux Standards Track [Page 9] RFC 5440 PCEP March 2009

 The ends of the PCEP session also run DeadTimers, and they restart
 the timers whenever a message is received on the session.  If one end
 of the session receives no message before the DeadTimer expires, it
 declares the session dead.
 Note that this means that the Keepalive message is unresponded and
 does not form part of a two-way keepalive handshake as used in some
 protocols.  Also note that the mechanism is designed to reduce to a
 minimum the amount of keepalive traffic on the session.
 The keepalive traffic on the session may be unbalanced according to
 the requirements of the session ends.  Each end of the session can
 specify (on an Open message) the Keepalive timer that it will use
 (i.e., how often it will transmit a Keepalive message if there is no
 other traffic) and a DeadTimer that it recommends its peer to use
 (i.e., how long the peer should wait before declaring the session
 dead if it receives no traffic).  The session ends may use different
 Keepalive timer values.
 The minimum value of the Keepalive timer is 1 second, and it is
 specified in units of 1 second.  The recommended default value is 30
 seconds.  The timer may be disabled by setting it to zero.
 The recommended default for the DeadTimer is 4 times the value of the
 Keepalive timer used by the remote peer.  This means that there is
 never any risk of congesting TCP with excessive Keepalive messages.

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

Vasseur & Le Roux Standards Track [Page 10] RFC 5440 PCEP March 2009

 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=B
 Mbit/s, Setup/Holding priority=P, ...".  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 address pair.  The process is shown in a schematic
 form in Figure 2.
 Note that multiple path computation requests may be outstanding from
 a PCC to a PCE at any time.
 Details about the PCReq message can be found in Section 6.4.

4.2.4. Path Computation Reply Sent by The PCE to a PCC

               +-+-+                  +-+-+
               |PCC|                  |PCE|
               +-+-+                  +-+-+
                 |                      |
                 |---- PCReq message--->|
                 |                      |1) Path computation
                 |                      |   request received
                 |                      |
                 |                      |2) Path successfully
                 |                      |   computed
                 |                      |
                 |                      |3) Computed paths
                 |                      |   sent to the PCC
                 |                      |
                 |<--- PCRep message ---|
                 |    (Positive reply)  |
     Figure 3a: Path Computation Request With Successful
                     Path Computation

Vasseur & Le Roux Standards Track [Page 11] RFC 5440 PCEP March 2009

               +-+-+                  +-+-+
               |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 be either:
 o  Positive (Figure 3a): the PCE manages to compute a path that
    satisfies the set of required constraints.  In this case, the PCE
    returns the set of computed paths to the requesting PCC.  Note
    that PCEP supports the capability to send a single request that
    requires the computation of more than one path (e.g., computation
    of a set of link-diverse paths).
 o  Negative (Figure 3b): no path could be found that satisfies the
    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.

4.2.5. Notification

 There are several circumstances in which a PCE may want to notify a
 PCC of a specific event.  For example, suppose that the PCE suddenly
 gets overloaded, potentially leading 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.  Upon receiving such notification,

Vasseur & Le Roux Standards Track [Page 12] RFC 5440 PCEP March 2009

 the PCC may decide to redirect its path computation requests to
 another PCE should an alternate PCE be available.  Similarly, a PCC
 may desire to notify a PCE of a particular event such as the
 cancellation of pending requests.
                     +-+-+                  +-+-+
                     |PCC|                  |PCE|
                     +-+-+                  +-+-+
 1) Path computation   |                      |
    event              |                      |
 2) PCE Selection      |                      |
 3) Path computation   |---- PCReq message--->|
    request X sent to  |                      |4) Path computation
    the selected PCE   |                      |   request queued
                       |                      |
                       |                      |
 5) Path computation   |                      |
    request X cancelled|                      |
                       |---- PCNtf message -->|
                       |                      |6) Path computation
                       |                      |   request X cancelled
    Figure 4: Example of PCC Notification (Cancellation Notification)
                           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   |                      |   request queued
                       |                      |
                       |                      |
                       |                      |5) PCE gets overloaded
                       |                      |
                       |                      |
                       |                      |6) Path computation
                       |                      |   request X cancelled
                       |                      |
                       |<--- PCNtf message----|
   Figure 5: Example of PCE Notification (Cancellation Notification)
                          Sent to a PCC
 Details about the PCNtf message can be found in Section 6.6.

Vasseur & Le Roux Standards Track [Page 13] RFC 5440 PCEP March 2009

4.2.6. Error

 The PCEP Error message (also referred to as a PCErr message) is sent
 in several situations: when a protocol error condition is met or when
 the request is not compliant with the PCEP specification (e.g.,
 capability not supported, reception of a message with a mandatory
 missing object, policy violation, unexpected message, unknown request
 reference).
                    +-+-+                  +-+-+
                    |PCC|                  |PCE|
                    +-+-+                  +-+-+
 1) Path computation  |                      |
    event             |                      |
 2) PCE Selection     |                      |
 3) Path computation  |---- PCReq message--->|
    request X sent to |                      |4) Reception of a
    the selected PCE  |                      |   malformed object
                      |                      |
                      |                      |5) Request discarded
                      |                      |
                      |<-- PCErr message  ---|
                      |                      |
   Figure 6: Example of Error Message Sent by a PCE to a PCC
        in Reply to the Reception of a Malformed Object
 Details about the PCErr message can be found in Section 6.7.

4.2.7. 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 closes the TCP connection.
 If the PCEP session is terminated by the PCE, the PCC clears all the
 states related to pending requests previously 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 is immediately
 terminated.
 Details about the Close message can be found in Section 6.8.

Vasseur & Le Roux Standards Track [Page 14] RFC 5440 PCEP March 2009

4.2.8. Intermittent versus Permanent PCEP Session

 An implementation may decide to keep the PCEP session alive (and thus
 the corresponding TCP connection) for an unlimited time.  (For
 instance, this may be appropriate when path computation requests are
 sent on a frequent basis so as to avoid opening a TCP connection each
 time a path computation request is needed, which would incur
 additional processing delays.)  Conversely, in some other
 circumstances, it may be desirable to systematically open and close a
 PCEP session for each PCEP request (for instance, when sending a path
 computation request is a rare event).

5. Transport Protocol

 PCEP operates over TCP using a registered TCP port (4189).  This
 allows the requirements of reliable messaging and flow control to be
 met without further protocol work.  All PCEP messages MUST be sent
 using the registered TCP port for the source and destination TCP
 port.

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 for the
 message to be considered valid.  A PCEP message with a missing
 mandatory object MUST trigger an Error message (see Section 7.15).
 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 7.2).  When this flag is set in an
 object in a PCReq, the PCE MUST take the information carried in the
 object into account during the path computation.  For example, the
 METRIC object defined in Section 7.8 allows a PCC to specify a
 bounded acceptable path cost.  The METRIC object is optional, but a
 PCC may set a flag to ensure that the constraint is taken into
 account.  In this case, if the constraint cannot be taken into
 account by the PCE, the PCE MUST trigger an Error message.
 For each PCEP message type, rules are defined that specify the set of
 objects that the message can carry.  We use the Backus-Naur Form
 (BNF) (see [RBNF]) to specify such rules.  Square brackets refer to
 optional sub-sequences.  An implementation MUST form the PCEP
 messages using the object ordering specified in this document.

Vasseur & Le Roux Standards Track [Page 15] RFC 5440 PCEP March 2009

6.1. Common Header

   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 |       Message-Length          |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
              Figure 7: PCEP Message Common Header
 Ver (Version - 3 bits):  PCEP version number.  Current version is
    version 1.
 Flags (5 bits):  No flags are currently defined.  Unassigned bits are
    considered as reserved.  They MUST be set to zero on transmission
    and MUST be ignored on receipt.
 Message-Type (8 bits):  The following message types are currently
    defined:
       Value    Meaning
         1        Open
         2        Keepalive
         3        Path Computation Request
         4        Path Computation Reply
         5        Notification
         6        Error
         7        Close
 Message-Length (16 bits):  total length of the PCEP message including
    the common header, expressed in bytes.

6.2. Open Message

 The Open message is a PCEP message sent by a PCC to a PCE and by a
 PCE to a PCC in order to establish a PCEP session.  The Message-Type
 field of the PCEP common header for the Open message is set to 1.
 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 as specified in Appendix A.
 Any message received prior to an Open message MUST trigger a protocol
 error condition causing a PCErr message to be sent with Error-Type
 "PCEP session establishment failure" and Error-value "reception of an
 invalid Open message or a non Open message" and the PCEP session
 establishment attempt MUST be terminated by closing the TCP
 connection.

Vasseur & Le Roux Standards Track [Page 16] RFC 5440 PCEP March 2009

 The Open message is used to establish a PCEP session between the PCEP
 peers.  During the establishment phase, the PCEP peers exchange
 several session characteristics.  If both parties agree on such
 characteristics, the PCEP session is successfully established.
 The format of an Open message is as follows:
 <Open Message>::= <Common Header>
                   <OPEN>
 The Open message MUST contain exactly one OPEN object (see
 Section 7.3).
 Various session characteristics are specified within the OPEN object.
 Once the TCP connection has been successfully established, the sender
 MUST start an initialization timer called OpenWait after the
 expiration of which, if no Open message has been received, it sends a
 PCErr message and releases the TCP connection (see Appendix A for
 details).
 Once an Open message has been sent to a PCEP peer, the sender MUST
 start an initialization timer called KeepWait after the expiration of
 which, if neither a Keepalive message has been received nor a PCErr
 message in case of disagreement of the session characteristics, a
 PCErr message MUST be sent and the TCP connection MUST be released
 (see Appendix A for details).
 The OpenWait and KeepWait timers have a fixed value of 1 minute.
 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 characteristics is not acceptable
 to the receiving peer, it MUST send an Error message.  The Error
 message SHOULD also contain the related OPEN object and, 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 messages can be found in Section 7.15.
 Successive retries are permitted, but an implementation SHOULD make
 use of an exponential back-off session establishment retry procedure.
 If the PCEP session characteristics are acceptable, the receiving
 PCEP peer MUST send a Keepalive message (defined in Section 6.3) that
 serves as an acknowledgment.

Vasseur & Le Roux Standards Track [Page 17] RFC 5440 PCEP March 2009

 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 Keepalive message is also
 used in response to an Open message to acknowledge that an Open
 message has been received and that the PCEP session characteristics
 are acceptable.  The Message-Type field of the PCEP common header for
 the Keepalive message is set to 2.  The Keepalive message does not
 contain any object.
 PCEP has its own keepalive mechanism used to ensure 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 constraint 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 are no constraints mandating
 the use of identical DeadTimers by both PCEP peers.  The minimum
 Keepalive timer value is 1 second.  Deployments SHOULD consider
 carefully the impact of using low values for the Keepalive timer as
 these might not give rise to the expected results in periods of
 temporary network instability.
 Keepalive messages are sent at the frequency specified in the OPEN
 object carried within an Open message according to the rules
 specified in Section 7.3.  Because any PCEP message may serve as
 Keepalive, an implementation may either decide to send Keepalive
 messages at fixed intervals regardless of 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.
 Note that sending Keepalive messages to keep the session alive is
 optional, and PCEP peers may decide not to send Keepalive messages
 once the PCEP session is established; in which case, the peer that
 does not receive Keepalive messages does not expect to receive them
 and MUST NOT declare the session as inactive.
 The format of a Keepalive message is as follows:
 <Keepalive Message>::= <Common Header>

Vasseur & Le Roux Standards Track [Page 18] RFC 5440 PCEP March 2009

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 to request a path
 computation.  A PCReq message may carry more than one path
 computation request.  The Message-Type field of the PCEP common
 header for the PCReq message is set to 3.
 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
 or both of these objects is missing, the receiving PCE MUST send an
 error message to the requesting PCC.  Other objects are optional.
 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-list>]
                 [<RRO>[<BANDWIDTH>]]
                 [<IRO>]
                 [<LOAD-BALANCING>]
 where:
 <metric-list>::=<METRIC>[<metric-list>]
 The SVEC, RP, END-POINTS, LSPA, BANDWIDTH, METRIC, RRO, IRO, and
 LOAD-BALANCING objects are defined in Section 7.  The special case of
 two BANDWIDTH objects is discussed in detail in Section 7.7.
 A PCEP implementation is free to process received requests in any
 order.  For example, the requests may be processed in the order they
 are received, reordered and assigned priority according to local
 policy, reordered according to the priority encoded in the RP object
 (Section 7.4.1), or processed in parallel.

Vasseur & Le Roux Standards Track [Page 19] RFC 5440 PCEP March 2009

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 for the PCRep message is set to 4.
 The bundling of multiple replies to a set of path computation
 requests within a single PCRep message is supported by PCEP.  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 provide
 each computed path in separate PCRep messages or within the same
 PCRep message.  A PCRep message may contain positive and negative
 replies.
 A PCRep message may contain a set of computed paths corresponding to
 either a single path computation request with load-balancing (see
 Section 7.16) or multiple path computation requests originated by a
 requesting PCC.  The PCRep message may also contain multiple
 acceptable paths corresponding to the same request.
 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 7.4 for the definition of the RP object).
 If the path computation request can be satisfied (i.e., the PCE finds
 a set of paths that satisfy the set of constraints), the set of
 computed paths specified by means of Explicit Route Objects (EROs) is
 inserted in the PCRep message.  The ERO is defined in Section 7.9.
 The situation where multiple computed paths are provided in a PCRep
 message is discussed in detail in Section 7.13.  Furthermore, when a
 PCC requests the computation of a set of paths for a total amount of
 bandwidth by means of a LOAD-BALANCING object carried within a PCReq
 message, the ERO of each computed path may be followed by a BANDWIDTH
 object as discussed in section Section 7.16.
 If the path computation request cannot be satisfied, the PCRep
 message MUST include a NO-PATH object.  The NO-PATH object (described
 in Section 7.5) may also contain other information (e.g, reasons for
 the path computation failure).

Vasseur & Le Roux Standards Track [Page 20] RFC 5440 PCEP March 2009

 The format of a PCRep message is as follows:
 <PCRep Message> ::= <Common Header>
                     <response-list>
 where:
    <response-list>::=<response>[<response-list>]
    <response>::=<RP>
                [<NO-PATH>]
                [<attribute-list>]
                [<path-list>]
    <path-list>::=<path>[<path-list>]
    <path>::= <ERO><attribute-list>
 where:
  <attribute-list>::=[<LSPA>]
                     [<BANDWIDTH>]
                     [<metric-list>]
                     [<IRO>]
  <metric-list>::=<METRIC>[<metric-list>]

6.6. Notification (PCNtf) Message

 The PCEP Notification message (also referred to as the PCNtf message)
 can be sent either by a PCE to a PCC, or by a PCC to a PCE, to notify
 of a specific event.  The Message-Type field of the PCEP common
 header for the PCNtf message is set to 5.
 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 7.14.  The PCNtf message MAY also contain RP objects (see
 Section 7.4) when the notification refers to particular path
 computation requests.
 The PCNtf message may be sent by a PCC or a PCE in response to a
 request or in an unsolicited manner.

Vasseur & Le Roux Standards Track [Page 21] RFC 5440 PCEP March 2009

 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
 in several situations: when a protocol error condition is met or when
 the request is not compliant with the PCEP specification (e.g.,
 reception of a malformed message, reception of a message with a
 mandatory missing object, policy violation, unexpected message,
 unknown request reference).  The Message-Type field of the PCEP
 common header for the PCErr message is set to 6.
 The PCErr message is sent by a PCC or a PCE in response to a request
 or in an unsolicited manner.  If the PCErr message is sent in
 response to a request, the PCErr message MUST include the set of RP
 objects related to the pending path computation requests that
 triggered the error condition.  In the latter case (unsolicited), no
 RP object is inserted in the PCErr message.  For example, no RP
 object is inserted in a PCErr when the error condition occurred
 during the initialization phase.  A PCErr message MUST contain a
 PCEP-ERROR object specifying the PCEP error condition.  The PCEP-
 ERROR object is defined in Section 7.15.
 The format of a PCErr message is as follows:
 <PCErr Message> ::= <Common Header>
                     ( <error-obj-list> [<Open>] ) | <error>
                     [<error-list>]
 <error-obj-list>::=<PCEP-ERROR>[<error-obj-list>]
 <error>::=[<request-id-list>]
            <error-obj-list>
 <request-id-list>::=<RP>[<request-id-list>]

Vasseur & Le Roux Standards Track [Page 22] RFC 5440 PCEP March 2009

 <error-list>::=<error>[<error-list>]
 The procedure upon the receipt of a PCErr message is defined in
 Section 7.15.

6.8. Close Message

 The Close message is a PCEP message that is either sent by a PCC to a
 PCE or by a PCE to a PCC in order to close an established PCEP
 session.  The Message-Type field of the PCEP common header for the
 Close message is set to 7.
 The format of a Close message is as follows:
 <Close Message>::= <Common Header>
                    <CLOSE>
 The Close message MUST contain exactly one CLOSE object (see
 Section 6.8).  If more than one CLOSE object is present, the first
 MUST be processed and subsequent objects ignored.
 Upon the receipt of a valid Close message, the receiving PCEP peer
 MUST cancel all pending requests, it MUST close the TCP connection
 and MUST NOT send any further PCEP messages on the PCEP session.

6.9. Reception of Unknown Messages

 A PCEP implementation that receives an unrecognized PCEP message MUST
 send a PCErr message with Error-value=2 (capability not supported).
 If a PCC/PCE receives unrecognized messages at a rate equal or
 greater than MAX-UNKNOWN-MESSAGES unknown message requests per
 minute, the PCC/PCE MUST send a PCEP CLOSE message with close
 value="Reception of an unacceptable number of unknown PCEP message".
 A RECOMMENDED value for MAX-UNKNOWN-MESSAGES is 5.  The PCC/PCE MUST
 close the TCP session and MUST NOT send any further PCEP messages on
 the PCEP session.

7. Object Formats

 PCEP objects have a common format.  They begin with a common object
 header (see Section 7.2).  This is followed by object-specific fields
 defined for each different object.  The object may also include one
 or more type-length-value (TLV) encoded data sets.  Each TLV has the
 same structure as described in Section 7.1.

Vasseur & Le Roux Standards Track [Page 23] RFC 5440 PCEP March 2009

7.1. PCEP TLV Format

 A PCEP object may include a set of one or more optional TLVs.
 All PCEP TLVs have the following format:
 Type:   2 bytes
 Length: 2 bytes
 Value:  variable
 A PCEP object TLV is comprised of 2 bytes for the type, 2 bytes
 specifying the TLV length, and a value field.
 The Length field defines the length of the value portion in bytes.
 The TLV is padded to 4-bytes alignment; padding is not included in
 the Length field (so a 3-byte value would have a length of 3, but the
 total size of the TLV would be 8 bytes).
 Unrecognized TLVs MUST be ignored.
 IANA management of the PCEP Object TLV type identifier codespace is
 described in Section 9.

7.2. Common Object Header

 A PCEP object carried within a PCEP message consists of one or more
 32-bit words with a common header that 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 fields are managed by IANA.
    The Object-Class and Object-Type fields uniquely identify each
    PCEP object.

Vasseur & Le Roux Standards Track [Page 24] RFC 5440 PCEP March 2009

 Res flags (2 bits):  Reserved field.  This field MUST be set to zero
    on transmission and MUST be ignored on receipt.
 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.
 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 has no meaning in a
    PCRep message when the P flag has been set in the corresponding
    PCReq message.
 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" along with
 the corresponding RP object.  Note that if a PCReq includes multiple
 requests, only requests for which an object with the P flag set is
 unknown/unrecognized MUST be rejected.
 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.

7.3. OPEN Object

 The OPEN object MUST be present in each Open message and MAY be
 present in a 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
 version, Keepalive frequency, DeadTimer, and 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 TLVs are currently
 defined.

Vasseur & Le Roux Standards Track [Page 25] RFC 5440 PCEP March 2009

 OPEN Object-Class is 1.
 OPEN Object-Type is 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 |   Flags |   Keepalive   |  DeadTimer    |      SID      |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                                                               |
 //                       Optional TLVs                         //
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                  Figure 9: OPEN Object Format
 Ver (3 bits):  PCEP version.  Current version is 1.
 Flags (5 bits):  No flags are currently defined.  Unassigned bits are
    considered as reserved.  They MUST be set to zero on transmission
    and MUST be ignored on receipt.
 Keepalive (8 bits):  maximum period of time (in seconds) between two
    consecutive PCEP messages sent by the sender of this message.  The
    minimum value for the Keepalive is 1 second.  When set to 0, once
    the session is established, no further Keepalive messages are 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 the PCEP peer can declare the session with the
    sender of the Open message to be down if no PCEP message has been
    received.  The DeadTimer SHOULD be set to 0 and MUST be ignored if
    the Keepalive is set to 0.  A RECOMMENDED value for the DeadTimer
    is 4 times the value of the Keepalive.
 Example:
 A sends an Open message to B with Keepalive=10 seconds and
 DeadTimer=40 seconds.  This means that A sends Keepalive messages (or
 any other PCEP message) to B every 10 seconds and B can declare the
 PCEP session with A down if no PCEP message has been received from A
 within any 40-second period.

Vasseur & Le Roux Standards Track [Page 26] RFC 5440 PCEP March 2009

 SID (PCEP session ID - 8 bits):  unsigned PCEP session number that
    identifies the current session.  The SID MUST be incremented each
    time a new PCEP session is established.  It is used for logging
    and troubleshooting purposes.  Each increment SHOULD have a value
    of 1 and may cause a wrap back to zero.
    The SID is used to disambiguate instances of sessions to the same
    peer.  A PCEP implementation could use a single source of SIDs
    across all peers, or one source for each peer.  The former might
    constrain the implementation to only 256 concurrent sessions.  The
    latter potentially requires more states.  There is one SID number
    in each direction.
 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 an OPEN object
 within the PCErr message so as to propose alternative acceptable
 session characteristic values.

7.4. 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 RP object is used to specify various characteristics
 of the path computation request.
 The P flag of the RP object MUST be set in PCReq and PCRep messages
 and MUST be cleared in PCNtf and PCErr messages.  If the RP object is
 received with the P flag set incorrectly according to the rules
 stated above, the receiving peer MUST send a PCErr message with
 Error-Type=10 and Error-value=1.  The corresponding path computation
 request MUST be cancelled by the PCE without further notification.

7.4.1. Object Definition

 RP Object-Class is 2.
 RP Object-Type is 1.

Vasseur & Le Roux Standards Track [Page 27] RFC 5440 PCEP March 2009

 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
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                          Flags                    |O|B|R| Pri |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                        Request-ID-number                      |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                                                               |
 //                      Optional TLVs                          //
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                Figure 10: RP Object Body Format
 The RP object body has a variable length and may contain additional
 TLVs.  No TLVs are currently defined.
 Flags (32 bits)
 The following flags are currently defined:
 o  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 a local matter; it MUST be set to 0 when
    unused.  Furthermore, the use of the path computation request
    priority by the PCE's 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 this case, it is RECOMMENDED
    that the PCC set the priority field to 0 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 PCCs.
    The ability of a PCE to support request prioritization MAY be
    dynamically discovered by the PCCs 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 to
    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

Vasseur & Le Roux Standards Track [Page 28] RFC 5440 PCEP March 2009

    the handling of request priorities: in other words, the path
    computation request has been honored but without taking the
    request priority into account.
 o  R (Reoptimization - 1 bit): when set, the requesting PCC specifies
    that the PCReq message relates to the reoptimization of an
    existing TE LSP.  For all TE LSPs except zero-bandwidth LSPs, when
    the R bit is set, an RRO (see Section 7.10) MUST be included in
    the PCReq message to show the path of the existing TE LSP.  Also,
    for all TE LSPs except zero-bandwidth LSPs, when the R bit is set,
    the existing bandwidth of the TE LSP to be reoptimized MUST be
    supplied in a BANDWIDTH object (see Section 7.7).  This BANDWIDTH
    object is in addition to the instance of that object used to
    describe the desired bandwidth of the reoptimized LSP.  For zero-
    bandwidth LSPs, the RRO and BANDWIDTH objects that report the
    characteristics of the existing TE LSP are optional.
 o  B (Bi-directional - 1 bit): when set, the PCC specifies that the
    path computation request relates to a bi-directional TE LSP that
    has the same traffic engineering requirements including fate
    sharing, protection and restoration, LSRs, TE links, and resource
    requirements (e.g., latency and jitter) in each direction.  When
    cleared, the TE LSP is unidirectional.
 o  O (strict/loose - 1 bit): when set, in a PCReq message, this
    indicates that a loose path is acceptable.  Otherwise, when
    cleared, this indicates to the PCE that a path exclusively made of
    strict hops is required.  In a PCRep message, when the O bit is
    set this indicates that the returned path is a loose path;
    otherwise (when the O bit is cleared), the returned path is made
    of strict hops.
 Unassigned bits are considered reserved.  They MUST be set to zero on
 transmission and MUST be ignored on receipt.
 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 is used for disambiguation between pending requests, and
    thus it MUST be changed (such as by incrementing it) each time a
    new request is sent to the PCE, and may wrap.
    The value 0x00000000 is considered invalid.
    If no path computation reply is received from the PCE (e.g., the
    request is dropped by the PCE because of memory overflow), and the
    PCC wishes to resend its request, the same Request-ID-number MUST
    be used.  Upon receiving a path computation request from a PCC

Vasseur & Le Roux Standards Track [Page 29] RFC 5440 PCEP March 2009

    with the same Request-ID-number, the PCE SHOULD treat the request
    as a new request.  An implementation MAY choose to cache path
    computation replies in order to quickly handle retransmission
    without having to process a path computation request twice (in the
    case that the first request was dropped or lost).  Upon receiving
    a path computation reply from a PCE with the same Request-ID-
    number, the PCC SHOULD silently discard the path computation
    reply.
    Conversely, different Request-ID-numbers 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.

7.4.2. Handling of the RP Object

 If a PCReq message is received that does not contain 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 O bit of the RP message carried within a PCReq message is
 cleared and local policy has been configured on the PCE to not
 provide explicit paths (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 cleared".
 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
 also provide the strict/loose path by including an RRO object in the
 PCReq message so as to avoid/limit double-bandwidth counting if and
 only if the TE LSP is a non-zero-bandwidth TE LSP.  If the PCC has
 not requested a strict path (O bit set), a reoptimization can still
 be requested by the PCC, but this requires that the PCE either be
 stateful (keep track of the previously computed path with the
 associated list of strict hops), or have the ability to retrieve the
 complete required path segment.  Alternatively, the PCC MUST inform
 the PCE about the working path and the associated list of strict hops
 in PCReq.  The absence of an RRO in the PCReq message for a non-zero-
 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".

Vasseur & Le Roux Standards Track [Page 30] RFC 5440 PCEP March 2009

 If a PCC/PCE receives a PCRep/PCReq message that contains an RP
 object referring to an unknown Request-ID-number, the PCC/PCE MUST
 send a PCErr message with Error-Type="Unknown request reference".
 This is used for debugging purposes.  If a PCC/PCE receives PCRep/
 PCReq messages with unknown requests at a rate equal or greater than
 MAX-UNKNOWN-REQUESTS unknown requests per minute, the PCC/PCE MUST
 send a PCEP CLOSE message with close value="Reception of an
 unacceptable number of unknown requests/replies".  A RECOMMENDED
 value for MAX-UNKNOWN-REQUESTS is 5.  The PCC/PCE MUST close the TCP
 session and MUST NOT send any further PCEP messages on the PCEP
 session.
 The reception of a PCEP message that contains an RP object referring
 to a Request-ID-number=0x00000000 MUST be treated in similar manner
 as an unknown request.

7.5. NO-PATH Object

 The NO-PATH object is used in PCRep messages in response to an
 unsuccessful path computation request (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.
 There are several categories of issue that can lead to a negative
 reply.  For example, the PCE chain might be broken (should there be
 more than one PCE involved in the path computation) or no path
 obeying the set constraints could be found.  The "NI (Nature of
 Issue)" field in the NO-PATH object is used to report the error
 category.
 Optionally, if the PCE supports such capability, the NO-PATH object
 MAY contain an optional NO-PATH-VECTOR TLV defined below and used to
 provide more information on the reasons that led to a negative reply.
 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 set of objects 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 (in which case, the
 value differs from the value in the original request).
 NO-PATH Object-Class is 3.
 NO-PATH Object-Type is 1.

Vasseur & Le Roux Standards Track [Page 31] RFC 5440 PCEP March 2009

 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
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |Nature of Issue|C|          Flags              |   Reserved    |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                                                               |
 //                      Optional TLVs                          //
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
               Figure 11: NO-PATH Object Format
 NI - Nature of Issue (8 bits):  The NI field is used to report the
    nature of the issue that led to a negative reply.  Two values are
    currently defined:
       0: No path satisfying the set of constraints could be found
       1: PCE chain broken
    The Nature of Issue field value can be used by the PCC for various
    purposes:
  • Constraint adjustment before reissuing a new path computation

request,

  • Explicit selection of a new PCE chain,
  • Logging of the error type for further action by the network

administrator.

    IANA management of the NI field codespace is described in
    Section 9.
 Flags (16 bits).
 The following flag is currently defined:
 o  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
    failing constraints are specified.  The C flag has no meaning and
    is ignored unless the NI field is set to 0x00.
 Unassigned bits are considered as reserved.  They MUST be set to zero
 on transmission and MUST be ignored on receipt.

Vasseur & Le Roux Standards Track [Page 32] RFC 5440 PCEP March 2009

 Reserved (8 bits):  This field MUST be set to zero on transmission
    and MUST be ignored on receipt.
 The NO-PATH object body has a variable length and may contain
 additional TLVs.  The only TLV currently defined is the NO-PATH-
 VECTOR TLV defined below.
 Example: consider the case of a PCC that sends a path computation
 request to a PCE for a TE LSP of X Mbit/s.  Suppose that PCE cannot
 find a path for X Mbit/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 reason for
 the unsuccessful computation is the bandwidth constraint (in this
 case, the NI field value is 0x00 and 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) where Y refers to
 the bandwidth for which a TE LSP with the same other characteristics
 (such as Setup/Holding priorities, TE LSP attribute, local
 protection, etc.) could have been computed.
 When the NO-PATH object is absent from a PCRep message, the path
 computation request has been fully satisfied and the corresponding
 paths are provided in the PCRep message.
 An optional TLV named NO-PATH-VECTOR MAY be included in the NO-PATH
 object in order to provide more information on the reasons that led
 to a negative reply.
 The NO-PATH-VECTOR TLV is compliant with the PCEP TLV format defined
 in Section 7.1 and is comprised of 2 bytes for the type, 2 bytes
 specifying the TLV length (length of the value portion in bytes)
 followed by a fixed-length 32-bit flags field.
 Type:   1
 Length: 4 bytes
 Value:  32-bit flags field
 IANA manages the space of flags carried in the NO-PATH-VECTOR TLV
 (see Section 9).
 The following flags are currently defined:
 o  Bit number: 31 - PCE currently unavailable
 o  Bit number: 30 - Unknown destination
 o  Bit number: 29 - Unknown source

Vasseur & Le Roux Standards Track [Page 33] RFC 5440 PCEP March 2009

7.6. END-POINTS Object

 The END-POINTS object is used in a PCReq message to specify the
 source IP address and the destination IP address of the path for
 which a path computation is requested.  The P flag of the END-POINTS
 object MUST be set.  If the END-POINTS object is received with the P
 flag cleared, the receiving peer MUST send a PCErr message with
 Error-Type=10 and Error-value=1.  The corresponding path computation
 request MUST be cancelled by the PCE without further notification.
 Note that the source and destination addresses specified in the END-
 POINTS object may correspond to the source and destination IP address
 of the TE LSP or to those of a path segment.  Two END-POINTS objects
 (for IPv4 and IPv6) are defined.
 END-POINTS Object-Class is 4.
 END-POINTS Object-Type is 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

Vasseur & Le Roux Standards Track [Page 34] RFC 5440 PCEP March 2009

 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 bytes for IPv4 and
 32 bytes for IPv6.
 If more than one END-POINTS object is present, the first MUST be
 processed and subsequent objects ignored.

7.7. BANDWIDTH Object

 The BANDWIDTH object is used to specify the requested bandwidth for a
 TE LSP.  The notion of bandwidth is similar to the one used for RSVP
 signaling in [RFC2205], [RFC3209], and [RFC3473].
 If the requested bandwidth is equal to 0, the BANDWIDTH object is
 optional.  Conversely, if the requested bandwidth is not equal to 0,
 the PCReq message MUST contain a BANDWIDTH object.
 In the case of the reoptimization of a 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 values are defined that refer to the requested bandwidth
 and the bandwidth of the TE LSP for which a reoptimization is being
 performed.
 The BANDWIDTH object may be carried within PCReq and PCRep messages.
 BANDWIDTH Object-Class is 5.

Vasseur & Le Roux Standards Track [Page 35] RFC 5440 PCEP March 2009

 Two Object-Type values are defined for the BANDWIDTH object:
 o  Requested bandwidth: BANDWIDTH Object-Type is 1.
 o  Bandwidth of an existing TE LSP for which a reoptimization is
    requested.  BANDWIDTH Object-Type is 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 (see [IEEE.754.1985]), expressed in
    bytes per second.  Refer to Section 3.1.2 of [RFC3471] for a table
    of commonly used values.
 The BANDWIDTH object body has a fixed length of 4 bytes.

7.8. METRIC Object

 The METRIC object is optional and can be used for several purposes.
 In a PCReq message, a PCC MAY insert one or more METRIC objects:
 o  To indicate the metric that MUST be optimized by the path
    computation algorithm (IGP metric, TE metric, hop counts).
    Currently, three metrics are defined: the IGP cost, the TE metric
    (see [RFC3785]), and the number of hops traversed by a TE LSP.
 o  To indicate a bound on the path cost that 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.
 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.

Vasseur & Le Roux Standards Track [Page 36] RFC 5440 PCEP March 2009

 It must be understood that such path metrics are only meaningful if
 used consistently: for instance, if the delay of a computed path
 segment is exchanged between two PCEs 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 no constraints need be applied to
 any of the metrics.
 METRIC Object-Class is 6.
 METRIC Object-Type is 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
 The METRIC object body has a fixed length of 8 bytes.
 Reserved (16 bits):  This field MUST be set to zero on transmission
    and MUST be ignored on receipt.
 T (Type - 8 bits):  Specifies the metric type.
    Three values are currently defined:
    *  T=1: IGP metric
    *  T=2: TE metric
    *  T=3: Hop Counts
 Flags (8 bits):  Two flags are currently defined:
  • B (Bound - 1 bit): When set in a PCReq message, the metric-

value indicates a bound (a maximum) for the path metric that

       must not be exceeded for the PCC to consider the computed path
       as acceptable.  The path metric must be less than or equal to
       the value specified in the metric-value field.  When the B flag
       is cleared, the metric-value field is not used to reflect a
       bound constraint.

Vasseur & Le Roux Standards Track [Page 37] RFC 5440 PCEP March 2009

  • C (Computed Metric - 1 bit): When set in a PCReq message, this

indicates that the PCE MUST provide the computed path metric

       value (should a path satisfying the constraints be found) in
       the PCRep message for the corresponding metric.
    Unassigned flags MUST be set to zero on transmission and MUST be
    ignored on receipt.
 Metric-value (32 bits):  metric value encoded in 32 bits in IEEE
    floating point format (see [IEEE.754.1985]).
 Multiple METRIC objects MAY be inserted in a PCRep or a PCReq message
 for a given request (i.e., for a given RP).  For a given request,
 there MUST be at most one instance of the METRIC object for each
 metric type with the same B flag value.  If, for a given request, two
 or more instances of a METRIC object with the same B flag value are
 present for a metric type, only the first instance MUST be considered
 and other instances MUST be ignored.
 For a given request, the presence of two METRIC objects of the same
 type with a different value of the B flag is allowed.  Furthermore,
 it is also allowed to insert, for a given request, two METRIC objects
 with different types that have both their B flag cleared: in this
 case, an objective function must be used by the PCE to solve a multi-
 parameter optimization problem.
 A METRIC object used to indicate the metric to optimize during the
 path computation MUST have the B flag cleared and the C flag set to
 the appropriate value.  When the path computation relates to the
 reoptimization of an exiting TE LSP (in which case, the R flag of the
 RP object is set), an implementation MAY decide to set the metric-
 value field to the computed value of the metric of the TE LSP to be
 reoptimized with regards to a specific metric type.
 A METRIC object used to reflect a bound MUST have the B flag set, and
 the C flag and metric-value field set to the appropriate values.
 In a PCRep message, unless not allowed by PCE policy, at least one
 METRIC object MUST be present that reports the computed path metric
 if the C flag of the METRIC object was set in the corresponding path
 computation request (the B flag MUST be cleared).  The C flag has no
 meaning in a PCRep message.  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 computed path metric (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 the constraint metric that could be satisfied.

Vasseur & Le Roux Standards Track [Page 38] RFC 5440 PCEP March 2009

 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 objects are inserted in the PCReq
 message:
 o  First METRIC object with B=0, T=1, C=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 there is no policy that prevents the return of the computed
 metric, 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.

7.9. Explicit Route Object

 The ERO is used to encode the path of a TE LSP through the network.
 The ERO is carried within a PCRep message to provide the computed TE
 LSP if the path computation was successful.
 The contents of this object are identical in encoding to the contents
 of the Resource Reservation Protocol Traffic Engineering Extensions
 (RSVP-TE) Explicit Route Object (ERO) defined in [RFC3209],
 [RFC3473], and [RFC3477].  That is, the object is constructed from a
 series of sub-objects.  Any RSVP-TE ERO sub-object already defined or
 that could be defined in the future for use in the RSVP-TE ERO is
 acceptable in this object.
 PCEP ERO sub-object types correspond to RSVP-TE 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 7.
 ERO Object-Type is 1.

7.10. Reported Route Object

 The RRO is exclusively carried within a PCReq message so as to report
 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-

Vasseur & Le Roux Standards Track [Page 39] RFC 5440 PCEP March 2009

 objects.  Any RSVP-TE RRO sub-object already defined or that could be
 defined in the future for use in the RSVP-TE 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 RSVP-TE RRO.
 PCEP RRO sub-object types correspond to RSVP-TE RRO sub-object types.
 RRO Object-Class is 8.
 RRO Object-Type is 1.

7.11. LSPA Object

 The LSPA (LSP Attributes) object is optional and specifies various TE
 LSP attributes to be taken into account by the PCE during path
 computation.  The LSPA object can be carried within a PCReq message,
 or a PCRep message in case of unsuccessful path computation (in this
 case, the PCRep message also contains a NO-PATH object, and the LSPA
 object is used to indicate the set of constraints that could not be
 satisfied).  Most of the fields of the LSPA object are identical to
 the fields of the SESSION-ATTRIBUTE object (C-Type = 7) defined in
 [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.  See Section 4.7.4 of [RFC3209] for a
 detailed description of the use of resource affinities.
 LSPA Object-Class is 9.
 LSPA Object-Types is 1.

Vasseur & Le Roux Standards Track [Page 40] RFC 5440 PCEP March 2009

 The format of the LSPA object body is:
  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 TLVs                           //
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                Figure 16: LSPA Object Body Format
 Setup Prio (Setup Priority - 8 bits):  The priority of the TE LSP
    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 TE LSP
    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 (8 bits)
    L flag:  Corresponds to the "Local Protection Desired" bit
       ([RFC3209]) of the SESSION-ATTRIBUTE Object.  When set, this
       means that the computed path must include links protected with
       Fast Reroute as defined in [RFC4090].
    Unassigned flags MUST be set to zero on transmission and MUST be
    ignored on receipt.
 Reserved (8 bits):  This field MUST be set to zero on transmission
    and MUST be ignored on receipt.
 Note that optional TLVs may be defined in the future to carry
 additional TE LSP attributes such as those defined in [RFC5420].

Vasseur & Le Roux Standards Track [Page 41] RFC 5440 PCEP March 2009

7.12. Include Route Object

 The IRO (Include Route Object) is optional and can be used to specify
 that the computed path MUST traverse a set of specified network
 elements.  The IRO 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 cause the PCE to fail to find a
 path.
 IRO Object-Class is 10.
 IRO Object-Type is 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
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                                                               |
 //                        (Sub-objects)                        //
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                  Figure 17: IRO Body Format
 Sub-objects:  The IRO is made of sub-objects identical to the ones
    defined in [RFC3209], [RFC3473], and [RFC3477], where the IRO sub-
    object type is identical to the sub-object type defined in the
    related documents.
    The following sub-object types are supported.
        Type   Sub-object
         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.

7.13. SVEC Object

7.13.1. Notion of Dependent and Synchronized Path Computation Requests

 Independent versus dependent path computation requests: path
 computation requests are said to be independent if they are not
 related to each other.  Conversely, a set of dependent path
 computation requests is such that their computations cannot be
 performed independently of each other (a typical example of dependent
 requests is the computation of a set of diverse paths).

Vasseur & Le Roux Standards Track [Page 42] RFC 5440 PCEP March 2009

 Synchronized versus non-synchronized path computation requests: 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 non-synchronized.  Note that the
 PCC may chose to distribute the set of N requests across K PCEs for
 load balancing purposes.  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
 bundled within a single PCReq message (since PCEP allows for the
 bundling of multiple path computation requests within a single PCReq
 message).  That said, even in the case of independent requests, 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 Mbit/s and N2 Mbit/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 constraint 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
 setup failure probability compared to the serialized computation of
 independent requests.
 Dependent path computations are usually synchronized.  For example,
 in the case of the computation of M diverse paths, if such paths are
 computed in a non-synchronized fashion, this seriously increases the

Vasseur & Le Roux Standards Track [Page 43] RFC 5440 PCEP March 2009

 probability of not being able to satisfy all requests (sometimes also
 referred to as the well-known "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.
 Conversely, a set of independent path computation requests may or may
 not be synchronized.
 The synchronization of a set of path computation requests is achieved
 by using the SVEC object that specifies the list of synchronized
 requests that can either be dependent or independent.
 PCEP supports the following three modes:
 o  Bundle of a set of independent and non-synchronized path
    computation requests,
 o  Bundle of a set of independent and synchronized path computation
    requests (requires the SVEC object defined below),
 o  Bundle of a set of dependent and synchronized path computation
    requests (requires the SVEC object defined below).

7.13.2. SVEC Object

 Section 7.13.1 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 the synchronization of a set of dependent or independent path
 computation requests.  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
 request the synchronization 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 11.
 SVEC Object-Type is 1.

Vasseur & Le Roux Standards Track [Page 44] RFC 5440 PCEP March 2009

 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 18: SVEC Body Object Format
 Reserved (8 bits):  This field MUST be set to zero on transmission
    and MUST be ignored on receipt.
 Flags (24 bits):  Defines the potential dependency between the set of
    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).
    In case of a set of M synchronized independent path computation
    requests, the bits L, N, and S are cleared.
 Unassigned flags MUST be set to zero on transmission and MUST be
 ignored on receipt.
 The flags defined above are not exclusive.

7.13.3. 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 a potential dependency.
 The set of M path computation requests may be sent within a single
 PCReq message or multiple PCReq messages.  In the latter case, it is
 RECOMMENDED for the PCE to implement a local timer (called the

Vasseur & Le Roux Standards Track [Page 45] RFC 5440 PCEP March 2009

 SyncTimer) activated upon the receipt of the first PCReq message that
 contains the SVEC object after the expiration of which, if all the M
 path computation requests have not been received, a protocol error is
 triggered.  When a PCE receives a path computation request that
 cannot be satisfied (for example, because the PCReq message contains
 an object with the P bit set that is not supported), the PCE sends a
 PCErr message for this request (see Section 7.2), the PCE MUST cancel
 the whole set of related path computation requests and MUST send a
 PCErr message with Error-Type="Synchronized path computation request
 missing".
 Note that such PCReq messages may also contain non-synchronized path
 computation requests.  For example, the PCReq message may comprise N
 synchronized path computation requests that are related to RP 1, ...,
 RP N and are listed in the SVEC object along with any other path
 computation requests that are processed as normal.

7.14. 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 12.
 NOTIFICATION Object-Type is 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 TLVs                          //
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
             Figure 19: NOTIFICATION Body Object Format
 Reserved (8 bits):  This field MUST be set to zero on transmission
    and MUST be ignored on receipt.
 Flags (8 bits):  No flags are currently defined.  Unassigned flags
    MUST be set to zero on transmission and MUST be ignored on
    receipt.

Vasseur & Le Roux Standards Track [Page 46] RFC 5440 PCEP March 2009

 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.
 Both the Notification-type and Notification-value are 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 requests. A

Notification-type=1, Notification-value=1 indicates that the

       PCC wants to inform a PCE of the cancellation of a set of
       pending requests.  Such an event could be triggered because of
       external conditions such as the receipt of a positive reply
       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 events local to the PCC.  A NOTIFICATION object
       with Notification-type=1, Notification-value=1 is carried
       within a PCNtf message sent by the PCC to the PCE.  The RP
       object corresponding to the cancelled request 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 a 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 requests. A

Notification-type=1, Notification-value=2 indicates that the

       PCE wants to inform a PCC of the cancellation of a set of
       pending requests.  A NOTIFICATION object with Notification-
       type=1, Notification-value=2 is carried within a PCNtf message
       sent by a PCE to a PCC.  The RP object corresponding to the
       cancelled request 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 PCE from a PCC, the PCE MUST
       silently ignore the notification and no errors should be
       generated.
 o  Notification-type=2: Overloaded PCE
  • Notification-value=1: A Notification-type=2, Notification-

Vasseur & Le Roux Standards Track [Page 47] RFC 5440 PCEP March 2009

       value=1 indicates to the PCC that the PCE is currently in an
       overloaded state.  If no RP objects are included in the PCNtf
       message, this indicates that no other requests SHOULD be sent
       to that PCE until the overloaded state is cleared: the pending
       requests are not affected and will be served.  If some pending
       requests cannot be served due to the overloaded state, the PCE
       MUST also include a set of RP objects that identifies the set
       of pending requests that are 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 objects.  If
       such notification is received by a PCE from a PCC, the PCE MUST
       silently ignore the notification and no errors should be
       generated.
  • A PCE implementation SHOULD use a dual-threshold mechanism used

to determine whether it is in a congestion state with regards

       to specific resource monitoring (e.g.  CPU, memory).  The use
       of such thresholds is to avoid oscillations between overloaded/
       non-overloaded state that may result in oscillations of request
       targets by the PCCs.
  • Optionally, a TLV named OVERLOADED-DURATION may be included in

the NOTIFICATION object that specifies the period of time

       during which no further request should be sent to the PCE.
       Once this period of time has elapsed, the PCE should no longer
       be considered in a congested state.
       The OVERLOADED-DURATION TLV is compliant with the PCEP TLV
       format defined in Section 7.1 and is comprised of 2 bytes for
       the type, 2 bytes specifying the TLV length (length of the
       value portion in bytes), followed by a fixed-length value field
       of a 32-bit flags field.
       Type:   2
       Length: 4 bytes
       Value:  32-bit flags field indicates the estimated PCE
               congestion duration in seconds.
  • Notification-value=2: A Notification-type=2, Notification-

value=2 indicates that the PCE is no longer in an overloaded

       state and is available to process new path computation
       requests.  An implementation SHOULD 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 an OVERLOADED-DURATION TLV has been included in the
       corresponding message and the PCE wishes to wait for the

Vasseur & Le Roux Standards Track [Page 48] RFC 5440 PCEP March 2009

       expiration of that period of time before receiving new
       requests.  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 state and congestion state release
       notifications.  For example, an implementation could make use
       of an hysteresis approach using a dual-threshold mechanism that
       triggers the sending of congestion state notifications.
       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 oscillation of path computation requests.
 When a PCC receives an overload indication from a PCE, it should
 consider the impact on the entire network.  It must be remembered
 that other PCCs may also receive the notification, and so many path
 computation requests could be redirected to other PCEs.  This may, in
 turn, cause further overloading at PCEs in the network.  Therefore,
 an application at a PCC receiving an overload notification should
 consider applying some form of back-off (e.g., exponential) to the
 rate at which it generates path computation requests into the
 network.  This is especially the case as the number of PCEs reporting
 overload grows.

7.15. PCEP-ERROR Object

 The PCEP-ERROR object is exclusively carried within a PCErr message
 to notify of a PCEP error.
 PCEP-ERROR Object-Class is 13.
 PCEP-ERROR Object-Type is 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 TLVs                           //
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
             Figure 20: PCEP-ERROR Object Body Format

Vasseur & Le Roux Standards Track [Page 49] RFC 5440 PCEP March 2009

 A PCEP-ERROR object is used to report a PCEP 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 are managed by IANA
 (see the IANA section).
 Reserved (8 bits):  This field MUST be set to zero on transmission
    and MUST be ignored on receipt.
 Flags (8 bits):  no flag is currently defined.  This flag MUST be set
    to zero on transmission and MUST be ignored on receipt.
 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 TLVs so as
 to provide further information about the encountered error.
 A single PCErr message may contain multiple PCEP-ERROR objects.

Vasseur & Le Roux Standards Track [Page 50] RFC 5440 PCEP March 2009

 For each PCEP error, an Error-Type and an Error-value are defined.
 Error-Type    Meaning
    1          PCEP session establishment failure
               Error-value=1: reception of an invalid Open message or
                              a non Open message.
               Error-value=2: no Open message received before the
                              expiration of the OpenWait timer
               Error-value=3: unacceptable and non-negotiable session
                              characteristics
               Error-value=4: unacceptable but negotiable session
                              characteristics
               Error-value=5: reception of a second Open message with
                              still unacceptable session
                              characteristics
               Error-value=6: reception of a PCErr message proposing
                              unacceptable session characteristics
               Error-value=7: No Keepalive or PCErr message received
                              before the expiration of the KeepWait
                              timer
    2          Capability not supported
    3          Unknown Object
                Error-value=1: Unrecognized object class
                Error-value=2: Unrecognized object Type
    4          Not supported object
                Error-value=1: Not supported object class
                Error-value=2: Not supported object Type
    5          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)
    6          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)
                               when bandwidth is not equal to 0.
                Error-value=3: END-POINTS object missing
    7          Synchronized path computation request missing
    8          Unknown request reference
    9          Attempt to establish a second PCEP session
    10         Reception of an invalid object
                Error-value=1: reception of an object with P flag not
                set although the P flag must be set according to this
                specification.

Vasseur & Le Roux Standards Track [Page 51] RFC 5440 PCEP March 2009

 The error types listed above are described below.
 Error-Type=1: PCEP session establishment failure.
    If a malformed message is received, the receiving PCEP peer MUST
    send a PCErr message with Error-Type=1, Error-value=1.
    If no Open message is received before the expiration of the
    OpenWait timer, the receiving PCEP peer MUST send a PCErr message
    with Error-Type=1, Error-value=2 (see Appendix A for details).
    If one or more PCEP session characteristics are unacceptable by
    the receiving peer and are not negotiable, it MUST send a PCErr
    message with Error-Type=1, Error-value=3.
    If an Open message is received with unacceptable session
    characteristics but these characteristics are negotiable, the
    receiving PCEP peer MUST send a PCErr message with Error-Type-1,
    Error-value=4 (see Section 6.2 for details).
    If a second Open message is received during the PCEP session
    establishment phase and the session characteristics are still
    unacceptable, the receiving PCEP peer MUST send a PCErr message
    with Error-Type-1, Error-value=5 (see Section 6.2 for details).
    If a PCErr message is received during the PCEP session
    establishment phase that contains an Open message proposing
    unacceptable session characteristics, the receiving PCEP peer MUST
    send a PCErr message with Error-Type=1, Error-value=6.
    If neither a Keepalive message nor a PCErr message is received
    before the expiration of the KeepWait timer during the PCEP
    session establishment phase, the receiving PCEP peer MUST send a
    PCErr message with Error-Type=1, Error-value=7.
 Error-Type=2:  the PCE indicates that the path computation request
    cannot be honored because it does not support one or more required
    capability.  The corresponding path computation request MUST be
    cancelled.
 Error-Type=3 or Error-Type=4:  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=3 and 4,
    respectively).  In addition, the PCE MAY include in the PCErr
    message the unknown or not supported object.  The corresponding
    path computation request MUST be cancelled by the PCE without
    further notification.

Vasseur & Le Roux Standards Track [Page 52] RFC 5440 PCEP March 2009

 Error-Type=5:  if a path computation request is received that 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=5).  The corresponding path computation MUST be cancelled.
    Policy-specific TLVs carried within the PCEP-ERROR object may be
    defined in other documents to specify the nature of the policy
    violation.
 Error-Type=6:  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=6).  If there are multiple
    mandatory objects missing, the PCErr message MUST contain one
    PCEP-ERROR object per missing object.  The corresponding path
    computation MUST be cancelled.
 Error-Type=7:  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 7.13.3, the PCE MUST send a PCErr message with a PCEP-
    ERROR object (Error-Type=7).  The corresponding synchronized path
    computation MUST be cancelled.  It is RECOMMENDED for the PCE to
    include the REQ-MISSING TLVs (defined below) that identify the
    missing requests.
    The REQ-MISSING TLV is compliant with the PCEP TLV format defined
    in section 7.1 and is comprised of 2 bytes for the type, 2 bytes
    specifying the TLV length (length of the value portion in bytes),
    followed by a fixed-length value field of 4 bytes.
       Type:   3
       Length: 4 bytes
       Value:  4 bytes that indicate the Request-ID-number that
               corresponds to the missing request.
 Error-Type=8:  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=8).  In addition, the
    PCC MUST include in the PCErr message the unknown RP object.
 Error-Type=9:  if a PCEP peer detects an attempt from another PCEP
    peer to establish a second PCEP session, it MUST send a PCErr
    message with Error-Type=9, Error-value=1.  The existing PCEP
    session MUST be preserved and all subsequent messages related to
    the tentative establishment of the second PCEP session MUST be
    silently ignored.

Vasseur & Le Roux Standards Track [Page 53] RFC 5440 PCEP March 2009

 Error-Type=10:  if a PCEP peers receives an object with the P flag
    not set although the P flag must be set according to this
    specification, it MUST send a PCErr message with Error-Type=10,
    Error-value=1.

7.16. LOAD-BALANCING Object

 There are situations where no TE LSP with a bandwidth of X could be
 found by a PCE although such a bandwidth requirement could be
 satisfied by a set of TE LSPs such that the sum of their bandwidths
 is equal to X.  Thus, it might be useful for a PCC to request a set
 of TE LSPs so that the sum of their bandwidth is equal to X Mbit/s,
 with potentially some constraints on the number of TE LSPs and the
 minimum bandwidth of each of these TE LSPs.  Such a request is made
 by inserting a LOAD-BALANCING object in a PCReq message sent to a
 PCE.
 The LOAD-BALANCING object is optional.
 LOAD-BALANCING Object-Class is 14.
 LOAD-BALANCING Object-Type is 1.
 The format of the LOAD-BALANCING 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     |     Max-LSP   |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                        Min-Bandwidth                          |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
              Figure 21: LOAD-BALANCING Object Body Format
 Reserved (16 bits):  This field MUST be set to zero on transmission
    and MUST be ignored on receipt.
 Flags (8 bits):  No flag is currently defined.  The Flags field MUST
    be set to zero on transmission and MUST be ignored on receipt.
 Max-LSP (8 bits):  maximum number of TE LSPs in the set.
 Min-Bandwidth (32 bits):  Specifies the minimum bandwidth of each
    element of the set of TE LSPs.  The bandwidth is encoded in 32
    bits in IEEE floating point format (see [IEEE.754.1985]),
    expressed in bytes per second.

Vasseur & Le Roux Standards Track [Page 54] RFC 5440 PCEP March 2009

 The LOAD-BALANCING object body has a fixed length of 8 bytes.
 If a PCC requests the computation of a set of TE LSPs so that the sum
 of their bandwidth is X, the maximum number of TE LSPs is N, and each
 TE LSP must at least have a bandwidth of B, it inserts a BANDWIDTH
 object specifying X as the required bandwidth and a LOAD-BALANCING
 object with the Max-LSP and Min-Bandwidth fields set to N and B,
 respectively.

7.17. CLOSE Object

 The CLOSE object MUST be present in each Close message.  There MUST
 be only one CLOSE object per Close message.  If a Close message is
 received that contains more than one CLOSE object, the first CLOSE
 object is the one that must be processed.  Other CLOSE objects MUST
 be silently ignored.
 CLOSE Object-Class is 15.
 CLOSE Object-Type is 1.
 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 TLVs                       //
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                  Figure 22: CLOSE Object Format
 Reserved (16 bits):  This field MUST be set to zero on transmission
    and MUST be ignored on receipt.
 Flags (8 bits):  No flags are currently defined.  The Flag field MUST
    be set to zero on transmission and MUST be ignored on receipt.
 Reason (8 bits):  specifies the reason for closing the PCEP session.
    The setting of this field is optional.  IANA manages the codespace
    of the Reason field.  The following values are currently defined:

Vasseur & Le Roux Standards Track [Page 55] RFC 5440 PCEP March 2009

     Reasons
      Value        Meaning
        1          No explanation provided
        2          DeadTimer expired
        3          Reception of a malformed PCEP message
        4          Reception of an unacceptable number of unknown
                   requests/replies
        5          Reception of an unacceptable number of unrecognized
                   PCEP messages
 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

 This section follows the guidance of [PCE-MANAGE].

8.1. Control of Function and Policy

 A PCEP implementation SHOULD allow configuring the following PCEP
 session parameters on the implementation:
 o  The local Keepalive and DeadTimer (i.e., parameters sent by the
    PCEP peer in an Open message),
 o  The maximum acceptable remote Keepalive and DeadTimer (i.e.,
    parameters received from a peer in an Open message),
 o  Whether negotiation is enabled or disabled,
 o  If negotiation is allowed, the minimum acceptable Keepalive and
    DeadTimer timers received from a PCEP peer,
 o  The SyncTimer,
 o  The maximum number of sessions that can be set up,
 o  The request timer, the amount of time a PCC waits for a reply
    before resending its path computation requests (potentially to an
    alternate PCE),
 o  The MAX-UNKNOWN-REQUESTS,
 o  The MAX-UNKNOWN-MESSAGES.
 These parameters may be configured as default parameters for any PCEP
 session the PCEP speaker participates in, or may apply to a specific
 session with a given PCEP peer or to a specific group of sessions

Vasseur & Le Roux Standards Track [Page 56] RFC 5440 PCEP March 2009

 with a specific group of PCEP peers.  A PCEP implementation SHOULD
 allow configuring the initiation of a PCEP session with a selected
 subset of discovered PCEs.  Note that PCE selection is a local
 implementation issue.  A PCEP implementation SHOULD allow configuring
 a specific PCEP session with a given PCEP peer.  This includes the
 configuration of the following parameters:
 o  The IP address of the PCEP peer,
 o  The PCEP speaker role: PCC, PCE, or both,
 o  Whether the PCEP speaker should initiate the PCEP session or wait
    for initiation by the peer,
 o  The PCEP session parameters, as listed above, if they differ from
    the default parameters,
 o  A set of PCEP policies including the type of operations allowed
    for the PCEP peer (e.g., diverse path computation,
    synchronization, etc.).
 A PCEP implementation MUST allow restricting the set of PCEP peers
 that can initiate a PCEP session with the PCEP speaker (e.g., list of
 authorized PCEP peers, all PCEP peers in the area, all PCEP peers in
 the AS).

8.2. Information and Data Models

 A PCEP MIB module is defined in [PCEP-MIB] that describes managed
 objects for modeling of PCEP communication including:
 o  PCEP client configuration and status,
 o  PCEP peer configuration and information,
 o  PCEP session configuration and information,
 o  Notifications to indicate PCEP session changes.

8.3. Liveness Detection and Monitoring

 PCEP includes a keepalive mechanism to check the liveliness of a PCEP
 peer and a notification procedure allowing a PCE to advertise its
 overloaded state to a PCC.  Also, procedures in order to monitor the
 liveliness and performances of a given PCE chain (in case of
 multiple-PCE path computation) are defined in [PCE-MONITOR].

Vasseur & Le Roux Standards Track [Page 57] RFC 5440 PCEP March 2009

8.4. Verifying Correct Operation

 Verifying the correct operation of a PCEP communication can be
 performed by monitoring various parameters.  A PCEP implementation
 SHOULD provide the following parameters:
 o  Response time (minimum, average, and maximum), on a per-PCE-peer
    basis,
 o  PCEP session failures,
 o  Amount of time the session has been in active state,
 o  Number of corrupted messages,
 o  Number of failed computations,
 o  Number of requests for which no reply has been received after the
    expiration of a configurable timer and by verifying that at least
    one path exists that satisfies the set of constraints.
 A PCEP implementation SHOULD log error events (e.g., corrupted
 messages, unrecognized objects).

8.5. Requirements on Other Protocols and Functional Components

 PCEP does not put any new requirements on other protocols.  As PCEP
 relies on the TCP transport protocol, PCEP management can make use of
 TCP management mechanisms (such as the TCP MIB defined in [RFC4022]).
 The PCE Discovery mechanisms ([RFC5088], [RFC5089]) may have an
 impact on PCEP.  To avoid that a high frequency of PCE Discoveries/
 Disappearances triggers a high frequency of PCEP session setups/
 deletions, it is RECOMMENDED to introduce some dampening for
 establishment of PCEP sessions.

8.6. Impact on Network Operation

 In order to avoid any unacceptable impact on network operations, an
 implementation SHOULD allow a limit to be placed on the number of
 sessions that can be set up on a PCEP speaker, and MAY allow a limit
 to be placed on the rate of messages sent by a PCEP speaker and
 received from a peer.  It MAY also allow sending a notification when
 a rate threshold is reached.

Vasseur & Le Roux Standards Track [Page 58] RFC 5440 PCEP March 2009

9. IANA Considerations

 IANA assigns values to the PCEP protocol parameters (messages,
 objects, TLVs).
 IANA established a new top-level registry to contain all PCEP
 codepoints and sub-registries.
 The allocation policy for each new registry is by IETF Consensus: new
 values are assigned through the IETF consensus process (see
 [RFC5226]).  Specifically, new assignments are made via RFCs approved
 by the IESG.  Typically, the IESG will seek input on prospective
 assignments from appropriate persons (e.g., a relevant Working Group
 if one exists).

9.1. TCP Port

 PCEP has been registered as TCP port 4189.

9.2. PCEP Messages

 IANA created a registry for PCEP messages.  Each PCEP message has a
 message type value.
 Value     Meaning                          Reference
   1        Open                          This document
   2        Keepalive                     This document
   3        Path Computation Request      This document
   4        Path Computation Reply        This document
   5        Notification                  This document
   6        Error                         This document
   7        Close                         This document

9.3. PCEP Object

 IANA created a registry for PCEP objects.  Each PCEP object has an
 Object-Class and an Object-Type.
 Object-Class Value   Name                               Reference
        1             OPEN                               This document
                      Object-Type
                          1
        2             RP                                 This document
                      Object-Type
                          1

Vasseur & Le Roux Standards Track [Page 59] RFC 5440 PCEP March 2009

        3             NO-PATH                            This document
                      Object-Type
                          1
        4             END-POINTS                         This document
                      Object-Type
                          1: IPv4 addresses
                          2: IPv6 addresses
        5             BANDWIDTH                          This document
                      Object-Type
                        1: Requested bandwidth
                        2: Bandwidth of an existing TE LSP
                           for which a reoptimization is performed.
        6             METRIC                             This document
                      Object-Type
                          1
        7             ERO                                This document
                      Object-Type
                          1
        8             RRO                                This document
                      Object-Type
                          1
        9             LSPA                               This document
                      Object-Type
                          1
       10             IRO                                This document
                      Object-Type
                          1
       11             SVEC                               This document
                      Object-Type
                          1
       12             NOTIFICATION                       This document
                      Object-Type
                          1
       13             PCEP-ERROR                         This document
                      Object-Type
                          1

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       14             LOAD-BALANCING                     This document
                      Object-Type
                          1
       15             CLOSE                              This document
                      Object-Type
                          1

9.4. PCEP Message Common Header

 IANA created a registry to manage the Flag field of the PCEP Message
 Common Header.
 New bit numbers may be allocated only by an IETF Consensus action.
 Each bit should be tracked with the following qualities:
 o  Bit number (counting from bit 0 as the most significant bit)
 o  Capability description
 o  Defining RFC
 No bits are currently defined for the PCEP message common header.

9.5. Open Object Flag Field

 IANA created a registry to manage the Flag field of the OPEN object.
 New bit numbers may be allocated only by an IETF Consensus action.
 Each bit should be tracked with the following qualities:
 o  Bit number (counting from bit 0 as the most significant bit)
 o  Capability description
 o  Defining RFC
 No bits are currently for the OPEN Object flag field.

9.6. RP Object

 New bit numbers may be allocated only by an IETF Consensus action.
 Each bit should be tracked with the following qualities:
 o  Bit number (counting from bit 0 as the most significant bit)
 o  Capability description

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 o  Defining RFC
 Several bits are defined for the RP Object flag field in this
 document.  The following values have been assigned:
 Codespace of the Flag field (RP Object)
   Bit      Description              Reference
    26      Strict/Loose          This document
    27      Bi-directional        This document
    28      Reoptimization        This document
   29-31    Priority              This document

9.7. NO-PATH Object Flag Field

 IANA created a registry to manage the codespace of the NI field and
 the Flag field of the NO-PATH object.
  Value       Meaning                        Reference
    0    No path satisfying the set        This document
         of constraints could be found
    1    PCE chain broken                  This document
 New bit numbers may be allocated only by an IETF Consensus action.
 Each bit should be tracked with the following qualities:
 o  Bit number (counting from bit 0 as the most significant bit)
 o  Capability description
 o  Defining RFC
 One bit is defined for the NO-PATH Object flag field in this
 document:
 Codespace of the Flag field (NO-PATH Object)
   Bit      Description                      Reference
    0    Unsatisfied constraint indicated    This document

Vasseur & Le Roux Standards Track [Page 62] RFC 5440 PCEP March 2009

9.8. METRIC Object

 IANA created a registry to manage the codespace of the T field and
 the Flag field of the METRIC Object.
 Codespace of the T field (Metric Object)
  Value      Meaning          Reference
    1        IGP metric      This document
    2        TE metric       This document
    3        Hop Counts      This document
 New bit numbers may be allocated only by an IETF Consensus action.
 Each bit should be tracked with the following qualities:
 o  Bit number (counting from bit 0 as the most significant bit)
 o  Capability description
 o  Defining RFC
 Several bits are defined in this document.  The following values have
 been assigned:
 Codespace of the Flag field (Metric Object)
   Bit      Description         Reference
    6       Computed metric    This document
    7       Bound              This document

9.9. LSPA Object Flag Field

 IANA created a registry to manage the Flag field of the LSPA object.
 New bit numbers may be allocated only by an IETF Consensus action.
 Each bit should be tracked with the following qualities:
 o  Bit number (counting from bit 0 as the most significant bit)
 o  Capability description
 o  Defining RFC
 One bit is defined for the LSPA Object flag field in this document:

Vasseur & Le Roux Standards Track [Page 63] RFC 5440 PCEP March 2009

 Codespace of the Flag field (LSPA Object)
   Bit      Description             Reference
    7    Local Protection Desired   This document

9.10. SVEC Object Flag Field

 IANA created a registry to manage the Flag field of the SVEC object.
 New bit numbers may be allocated only by an IETF Consensus action.
 Each bit should be tracked with the following qualities:
 o  Bit number (counting from bit 0 as the most significant bit)
 o  Capability description
 o  Defining RFC
 Three bits are defined for the SVEC Object flag field in this
 document:
 Codespace of the Flag field (SVEC Object)
   Bit      Description      Reference
    21      SRLG Diverse     This document
    22      Node Diverse     This document
    23      Link Diverse     This document

9.11. NOTIFICATION Object

 IANA created a registry for the Notification-type and Notification-
 value of the NOTIFICATION object and manages the code space.
 Notification-type  Name                                 Reference
       1            Pending Request cancelled            This document
                    Notification-value
                      1: PCC cancels a set of pending requests
                      2: PCE cancels a set of pending requests
       2            Overloaded PCE                       This document
                    Notification-value
                      1: PCE in congested state
                      2: PCE no longer in congested state

Vasseur & Le Roux Standards Track [Page 64] RFC 5440 PCEP March 2009

 IANA created a registry to manage the Flag field of the NOTIFICATION
 object.
 New bit numbers may be allocated only by an IETF Consensus action.
 Each bit should be tracked with the following qualities:
 o  Bit number (counting from bit 0 as the most significant bit)
 o  Capability description
 o  Defining RFC
 No bits are currently for the Flag Field of the NOTIFICATION object.

9.12. PCEP-ERROR Object

 IANA created a registry for the Error-Type and Error-value of the
 PCEP Error Object and manages the code space.

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 For each PCEP error, an Error-Type and an Error-value are defined.

Error- Meaning Reference Type

1     PCEP session establishment failure                This document
      Error-value=1: reception of an invalid Open message or
                     a non Open message.
      Error-value=2: no Open message received before the expiration
                     of the OpenWait timer
      Error-value=3: unacceptable and non-negotiable session
                     characteristics
      Error-value=4: unacceptable but negotiable session
                     characteristics
      Error-value=5: reception of a second Open message with
                     still unacceptable session characteristics
      Error-value=6: reception of a PCErr message proposing
                     unacceptable session characteristics
      Error-value=7: No Keepalive or PCErr message received
                     before the expiration of the KeepWait timer
      Error-value=8: PCEP version not supported
2     Capability not supported                          This document
3     Unknown Object                                    This document
       Error-value=1: Unrecognized object class
       Error-value=2: Unrecognized object Type
4     Not supported object                              This document
       Error-value=1: Not supported object class
       Error-value=2: Not supported object Type
5     Policy violation                                  This document
       Error-value=1: C bit of the METRIC object set
                      (request rejected)
       Error-value=2: O bit of the RP object cleared
                      (request rejected)
6     Mandatory Object missing                          This document
       Error-value=1: RP object missing
       Error-value=2: RRO missing for a reoptimization
                      request (R bit of the RP object set)
       Error-value=3: END-POINTS object missing
7     Synchronized path computation request missing     This document
8     Unknown request reference                         This document
9     Attempt to establish a second PCEP session        This document

10 Reception of an invalid object This document

       Error-value=1: reception of an object with P flag
                      not set although the P flag must be
                      set according to this specification.
 IANA created a registry to manage the Flag field of the PCEP-ERROR
 object.

Vasseur & Le Roux Standards Track [Page 66] RFC 5440 PCEP March 2009

 New bit numbers may be allocated only by an IETF Consensus action.
 Each bit should be tracked with the following qualities:
 o  Bit number (counting from bit 0 as the most significant bit)
 o  Capability description
 o  Defining RFC
 No bits are currently for the Flag Field of the PCEP-ERROR Object.

9.13. LOAD-BALANCING Object Flag Field

 IANA created a registry to manage the Flag field of the LOAD-
 BALANCING object.
 New bit numbers may be allocated only by an IETF Consensus action.
 Each bit should be tracked with the following qualities:
 o  Bit number (counting from bit 0 as the most significant bit)
 o  Capability description
 o  Defining RFC
 No bits are currently for the Flag Field of the LOAD-BALANCING
 Object.

9.14. CLOSE Object

 The CLOSE object MUST be present in each Close message in order to
 close a PCEP session.  The reason field of the CLOSE object specifies
 the reason for closing the PCEP session.  The reason field of the
 CLOSE object is managed by IANA.
 Reasons
  Value        Meaning
    1          No explanation provided
    2          DeadTimer expired
    3          Reception of a malformed PCEP message
    4          Reception of an unacceptable number of unknown
               requests/replies
    5          Reception of an unacceptable number of unrecognized
               PCEP messages
 IANA created a registry to manage the flag field of the CLOSE object.

Vasseur & Le Roux Standards Track [Page 67] RFC 5440 PCEP March 2009

 New bit numbers may be allocated only by an IETF Consensus action.
 Each bit should be tracked with the following qualities:
 o  Bit number (counting from bit 0 as the most significant bit)
 o  Capability description
 o  Defining RFC
 No bits are currently for the Flag Field of the CLOSE Object.

9.15. PCEP TLV Type Indicators

 IANA created a registry for the PCEP TLVs.
  Value         Meaning                    Reference
    1          NO-PATH-VECTOR TLV         This document
    2          OVERLOAD-DURATION TLV      This document
    3          REQ-MISSING TLV            This document

9.16. NO-PATH-VECTOR TLV

 IANA manages the space of flags carried in the NO-PATH-VECTOR TLV
 defined in this document, numbering them from 0 as the least
 significant bit.
 New bit numbers may be allocated only by an IETF Consensus action.
 Each bit should be tracked with the following qualities:
 o  Bit number (counting from bit 0 as the most significant bit)
 o  Name flag
 o  Reference
 Bit Number       Name                         Reference
   31             PCE currently unavailable    This document
   30             Unknown destination          This document
   29             Unknown source               This document

Vasseur & Le Roux Standards Track [Page 68] RFC 5440 PCEP March 2009

10. Security Considerations

10.1. Vulnerability

 Attacks on PCEP may result in damage to active networks.  If path
 computation responses are changed, the PCC may be encouraged to set
 up inappropriate LSPs.  Such LSPs might deviate to parts of the
 network susceptible to snooping, or might transit congested or
 reserved links.  Path computation responses may be attacked by
 modification of the PCRep message, by impersonation of the PCE, or by
 modification of the PCReq to cause the PCE to perform a different
 computation from that which was originally requested.
 It is also possible to damage the operation of a PCE through a
 variety of denial-of-service attacks.  Such attacks can cause the PCE
 to become congested with the result that path computations are
 supplied too slowly to be of value for PCCs.  This could lead to
 slower-than-acceptable recovery times or delayed LSP establishment.
 In extreme cases, it may be that service requests are not satisfied.
 PCEP could be the target of the following attacks:
 o  Spoofing (PCC or PCE impersonation)
 o  Snooping (message interception)
 o  Falsification
 o  Denial of Service
 In inter-AS scenarios when PCE-to-PCE communication is required,
 attacks may be particularly significant with commercial as well as
 service-level implications.
 Additionally, snooping of PCEP requests and responses may give an
 attacker information about the operation of the network.  Simply by
 viewing the PCEP messages someone can determine the pattern of
 service establishment in the network and can know where traffic is
 being routed, thereby making the network susceptible to targeted
 attacks and the data within specific LSPs vulnerable.
 The following sections identify mechanisms to protect PCEP against
 security attacks.

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10.2. TCP Security Techniques

 At the time of writing, TCP-MD5 [RFC2385] is the only available
 security mechanism for securing the TCP connections that underly PCEP
 sessions.
 As explained in [RFC2385], the use of MD5 faces some limitations and
 does not provide as high a level of security as was once believed.  A
 PCEP implementation supporting TCP-MD5 SHOULD be designed so that
 stronger security keying techniques or algorithms that may be
 specified for TCP can be easily integrated in future releases.
 The TCP Authentication Option [TCP-AUTH] (TCP-AO) specifies new
 security procedures for TCP, but is not yet complete.  Since it is
 believed that [TCP-AUTH] will offer significantly improved security
 for applications using TCP, implementers should expect to update
 their implementation as soon as the TCP Authentication Option is
 published as an RFC.
 Implementations MUST support TCP-MD5 and should make the security
 function available as a configuration option.
 Operators will need to observe that some deployed PCEP
 implementations may pre-date the completion of [TCP-AUTH], and it
 will be necessary to configure policy for secure communication
 between PCEP speakers that support the TCP Authentication Option, and
 those that don't.
 An alternative approach for security over TCP transport is to use the
 Transport Layer Security (TLS) protocol [RFC5246].  This provides
 protection against eavesdropping, tampering, and message forgery.
 But TLS doesn't protect the TCP connection itself, because it does
 not authenticate the TCP header.  Thus, it is vulnerable to attacks
 such as TCP reset attacks (something against which TCP-MD5 does
 protect).  The use of TLS would, however, require the specification
 of how PCEP initiates TLS handshaking and how it interprets the
 certificates exchanged in TLS.  That specification is out of the
 scope of this document, but could be the subject of future work.

10.3. PCEP Authentication and Integrity

 Authentication and integrity checks allow the receiver of a PCEP
 message to know that the message genuinely comes from the node that
 purports to have sent it and to know whether the message has been
 modified.

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 The TCP-MD5 mechanism [RFC2385] described in the previous section
 provides such a mechanism subject to the concerns listed in [RFC2385]
 and [RFC4278].  These issues will be addressed and resolved by
 [TCP-AUTH].

10.4. 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 intercepts a PCE message
 could obtain sensitive information related to computed paths and
 resources.
 PCEP privacy can be ensured by encryption.  TCP MAY be run over IPsec
 [RFC4303] tunnels to provide the required encryption.  Note that
 IPsec can also ensure authentication and integrity; in which case,
 TCP-MD5 or TCP-AO would not be required.  However, there is some
 concern that IPsec on this scale would be hard to configure and
 operate.  Use of IPSec with PCEP is out of the scope of this document
 and may be addressed in a separate document.

10.5. Key Configuration and Exchange

 Authentication, tamper protection, and encryption all require the use
 of keys by sender and receiver.
 Although key configuration per session is possible, it may be
 particularly onerous to operators (in the same way as for the Border
 Gateway Protocol (BGP) as discussed in [BGP-SEC]).  If there is a
 relatively small number of PCCs and PCEs in the network, manual key
 configuration MAY be considered a valid choice by the operator,
 although it is important to be aware of the vulnerabilities
 introduced by such mechanisms (i.e., configuration errors, social
 engineering, and carelessness could all give rise to security
 breaches).  Furthermore, manually configured keys are less likely to
 be regularly updated which also increases the security risk.  Where
 there is a large number of PCCs and PCEs, the operator could find
 that key configuration and maintenance is a significant burden as
 each PCC needs to be configured to the PCE.
 An alternative to individual keys is the use of a group key.  A group
 key is common knowledge among all members of a trust domain.  Thus,
 since the routers in an IGP area or an AS are part of a common trust
 domain [MPLS-SEC], a PCEP group key MAY be shared among all PCCs and
 PCEs in an IGP area or AS.  The use of a group key will considerably
 simplify the operator's configuration task while continuing to secure

Vasseur & Le Roux Standards Track [Page 71] RFC 5440 PCEP March 2009

 PCEP against attack from outside the network.  However, it must be
 noted that the more entities that have access to a key, the greater
 the risk of that key becoming public.
 With the use of a group key, separate keys would need to be
 configured for the PCE-to-PCE communications that cross trust domain
 (e.g., AS) boundaries, but the number of these relationships is
 likely to be very small.
 PCE discovery ([RFC5088] and [RFC5089]) is a significant feature for
 the successful deployment of PCEP in large networks.  This mechanism
 allows a PCC to discover the existence of suitable PCEs within the
 network without the necessity of configuration.  It should be obvious
 that, where PCEs are discovered and not configured, the PCC cannot
 know the correct key to use.  There are three possible approaches to
 this problem that retain some aspect of security:
 o  The PCCs may use a group key as previously discussed.
 o  The PCCs may use some form of secure key exchange protocol with
    the PCE (such as the Internet Key Exchange protocol v2 (IKE)
    [RFC4306]).  The drawback to this is that IKE implementations on
    routers are not common and this may be a barrier to the deployment
    of PCEP.  Details are out of the scope of this document and may be
    addressed in a separate document.
 o  The PCCs may make use of a key server to determine the key to use
    when talking to the PCE.  To some extent, this is just moving the
    problem, since the PCC's communications with the key server must
    also be secure (for example, using Kerberos [RFC4120]), but there
    may some (minor) benefit in scaling if the PCC is to learn about
    several PCEs and only needs to know one key server.  Note that key
    servers currently have very limited implementation.  Details are
    out of the scope of this document and may be addressed in a
    separate document.
 PCEP relationships are likely to be long-lived even if the PCEP
 sessions are repeatedly closed and re-established.  Where protocol
 relationships persist for a large number of protocol interactions or
 over a long period of time, changes in the keys used by the protocol
 peers is RECOMMENDED [RFC4107].  Note that TCP-MD5 does not allow the
 key to be changed without closing and reopening the TCP connection
 which would result in the PCEP session being terminated and needing
 to be restarted.  That might not be a significant issue for PCEP.
 Note also that the plans for the TCP Authentication Option [TCP-AUTH]
 will allow dynamic key change (roll-over) for an active TCP
 connection.

Vasseur & Le Roux Standards Track [Page 72] RFC 5440 PCEP March 2009

 If key exchange is used (for example, through IKE), then it is
 relatively simple to support dynamic key updates and apply these to
 PCEP.
 Note that in-band key management for the TCP Authentication Option
 [TCP-AUTH] is currently unresolved.
 [RFC3562] sets out some of the issues for the key management of
 secure TCP connections.

10.6. Access Policy

 Unauthorized access to PCE function represents a variety of potential
 attacks.  Not only may this be a simple denial-of-service attack (see
 Section 10.7), but it would be a mechanism for an intruder to
 determine important information about the network and operational
 network policies simply by inserting bogus computation requests.
 Furthermore, false computation requests could be used to predict
 where traffic will be placed in the network when real requests are
 made, allowing the attacker to target specific network resources.
 PCEs SHOULD be configurable for access policy.  Where authentication
 is used, access policy can be achieved through the exchange or
 configuration of keys as described in Section 10.5.  More simple
 policies MAY be configured on PCEs in the form of access lists where
 the IP addresses of the legitimate PCCs are listed.  Policies SHOULD
 also be configurable to limit the type of computation requests that
 are supported from different PCCs.
 It is RECOMMENDED that access policy violations are logged by the PCE
 and are available for inspection by the operator to determine whether
 attempts have been made to attack the PCE.  Such mechanisms MUST be
 lightweight to prevent them from being used to support denial-of-
 service attacks (see Section 10.7).

10.7. Protection against Denial-of-Service Attacks

 Denial-of-service (DoS) attacks could be mounted at the TCP level or
 at the PCEP level.  That is, the PCE could be attacked through
 attacks on TCP or through attacks within established PCEP sessions.

10.7.1. Protection against TCP DoS Attacks

 PCEP can be the target of TCP DoS attacks, such as for instance SYN
 attacks, as is the case for all protocols that run over TCP.  Other
 protocol specifications have investigated this problem and PCEP can
 share their experience.  The reader is referred to the specification

Vasseur & Le Roux Standards Track [Page 73] RFC 5440 PCEP March 2009

 of the Label Distribution Protocol (LDP) [RFC5036] for example.  In
 order to protect against TCP DoS attacks, PCEP implementations can
 support the following techniques.
 o  PCEP uses a single registered port for all communications.  The
    PCE SHOULD listen for TCP connections only on ports where
    communication is expected.
 o  The PCE MAY implement an access list to immediately reject (or
    discard) TCP connection attempts from unauthorized PCCs.
 o  The PCE SHOULD NOT allow parallel TCP connections from the same
    PCC on the PCEP-registered port.
 o  The PCE MAY require the use of the MD5 option on all TCP
    connections, and MAY reject (or discard) any connection setup
    attempt that does not use MD5.  A PCE MUST NOT accept any SYN
    packet for which the MD5 segment checksum is invalid.  Note,
    however, that the use of MD5 requires that the receiver use CPU
    resources to compute the checksum before it can decide to discard
    an otherwise acceptable SYN segment.

10.7.2. Request Input Shaping/Policing

 A PCEP implementation may be subject to DoS attacks within a
 legitimate PCEP session.  For example, a PCC might send a very large
 number of PCReq messages causing the PCE to become congested or
 causing requests from other PCCs to be queued.
 Note that the direct use of the Priority field on the RP object to
 prioritize received requests does not provide any protection since
 the attacker could set all requests to be of the highest priority.
 Therefore, it is RECOMMENDED that PCE implementations include input
 shaping/policing mechanisms that either throttle the requests
 received from any one PCC, or apply queuing or priority-degradation
 techniques to over-communicative PCCs.
 Such mechanisms MAY be set by default, but SHOULD be available for
 configuration.  Such techniques may be considered particularly
 important in multi-service-provider environments to protect the
 resources of one service provider from unwarranted, over-zealous, or
 malicious use by PCEs in another service provider.

Vasseur & Le Roux Standards Track [Page 74] RFC 5440 PCEP March 2009

11. Acknowledgments

 The authors would like to thank Dave Oran, Dean Cheng, Jerry Ash,
 Igor Bryskin, Carol Iturrade, Siva Sivabalan, Rich Bradford, Richard
 Douville, Jon Parker, Martin German, and Dennis Aristow for their
 very valuable input.  The authors would also like to thank Fabien
 Verhaeghe for the very fruitful discussions and useful suggestions.
 David McGrew and Brian Weis provided valuable input to the Security
 Considerations section.
 Ross Callon, Magnus Westerlund, Lars Eggert, Pasi Eronen, Tim Polk,
 Chris Newman, and Russ Housley provided important input during IESG
 review.

12. References

12.1. 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.
 [RFC2385]        Heffernan, A., "Protection of BGP Sessions via the
                  TCP MD5 Signature Option", RFC 2385, August 1998.
 [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.
 [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.

Vasseur & Le Roux Standards Track [Page 75] RFC 5440 PCEP March 2009

 [RFC5226]        Narten, T. and H. Alvestrand, "Guidelines for
                  Writing an IANA Considerations Section in RFCs",
                  BCP 26, RFC 5226, May 2008.

12.2. Informative References

 [BGP-SEC]        Christian, B. and T. Tauber, "BGP Security
                  Requirements", Work in Progress, November 2008.
 [IEEE.754.1985]  IEEE Standard 754, "Standard for Binary Floating-
                  Point Arithmetic", August 1985.
 [INTER-LAYER]    Oki, E., Roux, J., Kumaki, K., Farrel, A., and T.
                  Takeda, "PCC-PCE Communication and PCE Discovery
                  Requirements for Inter-Layer Traffic Engineering",
                  Work in Progress, January 2009.
 [MPLS-SEC]       Fang, L. and M. Behringer, "Security Framework for
                  MPLS and GMPLS Networks", Work in Progress,
                  November 2008.
 [PCE-MANAGE]     Farrel, A., "Inclusion of Manageability Sections in
                  PCE Working Group Drafts", Work in Progress,
                  January 2009.
 [PCE-MONITOR]    Vasseur, J., Roux, J., and Y. Ikejiri, "A set of
                  monitoring tools for Path Computation Element based
                  Architecture", Work in Progress, November 2008.
 [PCEP-MIB]       Stephan, E. and K. Koushik, "PCE communication
                  protocol (PCEP) Management Information Base",
                  Work in Progress, November 2008.
 [RBNF]           Farrel, A., "Reduced Backus-Naur Form (RBNF) A
                  Syntax Used in Various Protocol Specifications",
                  Work in Progress, November 2008.
 [RFC1321]        Rivest, R., "The MD5 Message-Digest Algorithm",
                  RFC 1321, April 1992.
 [RFC3471]        Berger, L., "Generalized Multi-Protocol Label
                  Switching (GMPLS) Signaling Functional Description",
                  RFC 3471, January 2003.
 [RFC3562]        Leech, M., "Key Management Considerations for the
                  TCP MD5 Signature Option", RFC 3562, July 2003.

Vasseur & Le Roux Standards Track [Page 76] RFC 5440 PCEP March 2009

 [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.
 [RFC4022]        Raghunarayan, R., "Management Information Base for
                  the Transmission Control Protocol (TCP)", RFC 4022,
                  March 2005.
 [RFC4101]        Rescorla, E. and IAB, "Writing Protocol Models",
                  RFC 4101, June 2005.
 [RFC4107]        Bellovin, S. and R. Housley, "Guidelines for
                  Cryptographic Key Management", BCP 107, RFC 4107,
                  June 2005.
 [RFC4120]        Neuman, C., Yu, T., Hartman, S., and K. Raeburn,
                  "The Kerberos Network Authentication Service (V5)",
                  RFC 4120, July 2005.
 [RFC4278]        Bellovin, S. and A. Zinin, "Standards Maturity
                  Variance Regarding the TCP MD5 Signature Option (RFC
                  2385) and the BGP-4 Specification", RFC 4278,
                  January 2006.
 [RFC4303]        Kent, S., "IP Encapsulating Security Payload (ESP)",
                  RFC 4303, December 2005.
 [RFC4306]        Kaufman, C., "Internet Key Exchange (IKEv2)
                  Protocol", RFC 4306, December 2005.
 [RFC5420]        Farrel, A., Ed., Papadimitriou, D., Vasseur, JP.,
                  and A. Ayyangarps, "Encoding of Attributes for MPLS
                  LSP Establishment Using Resource Reservation
                  Protocol Traffic Engineering (RSVP-TE)", RFC 5420,
                  February 2009.
 [RFC4655]        Farrel, A., Vasseur, J., and J. Ash, "A Path
                  Computation Element (PCE)-Based Architecture",
                  RFC 4655, August 2006.
 [RFC4657]        Ash, J. and J. Le Roux, "Path Computation Element
                  (PCE) Communication Protocol Generic Requirements",
                  RFC 4657, September 2006.
 [RFC4674]        Le Roux, J., "Requirements for Path Computation
                  Element (PCE) Discovery", RFC 4674, October 2006.

Vasseur & Le Roux Standards Track [Page 77] RFC 5440 PCEP March 2009

 [RFC4927]        Le Roux, J., "Path Computation Element Communication
                  Protocol (PCECP) Specific Requirements for Inter-
                  Area MPLS and GMPLS Traffic Engineering", RFC 4927,
                  June 2007.
 [RFC5036]        Andersson, L., Minei, I., and B. Thomas, "LDP
                  Specification", RFC 5036, October 2007.
 [RFC5088]        Le Roux, JL., Vasseur, JP., Ikejiri, Y., and R.
                  Zhang, "OSPF Protocol Extensions for Path
                  Computation Element (PCE) Discovery", RFC 5088,
                  January 2008.
 [RFC5089]        Le Roux, JL., Vasseur, JP., Ikejiri, Y., and R.
                  Zhang, "IS-IS Protocol Extensions for Path
                  Computation Element (PCE) Discovery", RFC 5089,
                  January 2008.
 [RFC5246]        Dierks, T. and E. Rescorla, "The Transport Layer
                  Security (TLS) Protocol Version 1.2", RFC 5246,
                  August 2008.
 [RFC5376]        Bitar, N., Zhang, R., and K. Kumaki, "Inter-AS
                  Requirements for the Path Computation Element
                  Communication Protocol (PCECP)", RFC 5376,
                  November 2008.
 [TCP-AUTH]       Touch, J., Mankin, A., and R. Bonica, "The TCP
                  Authentication Option", Work in Progress,
                  November 2008.

Vasseur & Le Roux Standards Track [Page 78] RFC 5440 PCEP March 2009

Appendix A. PCEP Finite State Machine (FSM)

 The section describes the PCEP finite state machine (FSM).  PCEP
 Finite State Machine
                        +-+-+-+-+-+-+<------+
                 +------| SessionUP |<---+  |
                 |      +-+-+-+-+-+-+    |  |
                 |                       |  |
                 |   +->+-+-+-+-+-+-+    |  |
                 |   |  | KeepWait  |----+  |
                 |   +--|           |<---+  |
                 |+-----+-+-+-+-+-+-+    |  |
                 ||          |           |  |
                 ||          |           |  |
                 ||          V           |  |
                 ||  +->+-+-+-+-+-+-+----+  |
                 ||  |  | OpenWait  |-------+
                 ||  +--|           |<------+
                 ||+----+-+-+-+-+-+-+<---+  |
                 |||         |           |  |
                 |||         |           |  |
                 |||         V           |  |
                 ||| +->+-+-+-+-+-+-+    |  |
                 ||| |  |TCPPending |----+  |
                 ||| +--|           |       |
                 |||+---+-+-+-+-+-+-+<---+  |
                 ||||        |           |  |
                 ||||        |           |  |
                 ||||        V           |  |
                 |||+--->+-+-+-+-+       |  |
                 ||+---->| Idle  |-------+  |
                 |+----->|       |----------+
                 +------>+-+-+-+-+
      Figure 23: PCEP Finite State Machine for the PCC
 PCEP defines the following set of variables:
 Connect:  the timer (in seconds) started after having initialized a
    TCP connection using the PCEP-registered TCP port.  The value of
    the Connect timer is 60 seconds.
 ConnectRetry:  the number of times the system has tried to establish
    a TCP connection with a PCEP peer without success.

Vasseur & Le Roux Standards Track [Page 79] RFC 5440 PCEP March 2009

 ConnectMaxRetry:  the maximum number of times the system tries to
    establish a TCP connection using the PCEP-registered TCP port
    before going back to the Idle state.  The value of the
    ConnectMaxRetry is 5.
 OpenWait:  the timer 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
    goes back to the Idle state.  The OpenWait timer has a fixed value
    of 60 seconds.
 KeepWait:  the timer 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 goes back to the Idle state.  The KeepWait timer
    has a fixed value of 60 seconds.
 OpenRetry:  the number of times the system has received an Open
    message with unacceptable PCEP session characteristics.
 The following two state variables are defined:
 RemoteOK:  a boolean that is set to 1 if the system has received an
    acceptable Open message.
 LocalOK:  a boolean that is 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 the 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, etc.) but no PCEP
 messages are accepted from any PCEP peer.  The system listens to the
 PCEP-registered TCP port.
 The following set of variables are initialized:
    TCPRetry=0,
    LocalOK=0,
    RemoteOK=0,
    OpenRetry=0.

Vasseur & Le Roux Standards Track [Page 80] RFC 5440 PCEP March 2009

 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 such as the automatic detection of a PCEP peer), the
 system:
 o  Initiates a TCP connection with the PCEP peer,
 o  Starts the Connect timer,
 o  Moves to the TCPPending state.
 Upon receiving a TCP connection on the PCEP-registered 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.
 If the connection establishment fails, the system remains in the Idle
 state.  Any other event received in the Idle state is ignored.
 It is expected that an implementation will use an exponentially
 increasing timer between automatically generated Initialization
 events and between retries of TCP connection establishment.
 TCPPending State:
 If the TCP connection establishment succeeds, the system:
 o  Sends an Open message,
 o  Starts the OpenWait timer,
 o  Moves to the OpenWait state.
 If the TCP connection establishment fails (an error is detected
 during the TCP connection establishment) or the Connect timer
 expires:
 o  If ConnectRetry = ConnectMaxRetry, the system moves to the Idle
    State.

Vasseur & Le Roux Standards Track [Page 81] RFC 5440 PCEP March 2009

 o  If ConnectRetry < ConnectMaxRetry, the system:
    1.  Initiates of a TCP connection with the PCEP peer,
    2.  Increments the ConnectRetry variable,
    3.  Restarts the Connect timer,
    4.  Stays in the TCPPending state.
 In response to any other event, the system releases the PCEP
 resources for that peer and moves back to the Idle state.
 OpenWait State:
 In the OpenWait state, the system waits for an Open message from its
 PCEP peer.
 If the system receives an Open message from the PCEP peer before the
 expiration of the OpenWait timer, the system first examines all of
 its sessions that are in the OpenWait or KeepWait state.  If another
 session with the same PCEP peer already exists (same IP address),
 then the system performs the following collision-resolution
 procedure:
 o  If the system has initiated the current session and it has a lower
    IP address than the PCEP peer, the system closes the TCP
    connection, releases the PCEP resources for the pending session,
    and moves back to the Idle state.
 o  If the session was initiated by the PCEP peer and the system has a
    higher IP address that the PCEP peer, the system closes the TCP
    connection, releases the PCEP resources for the pending session,
    and moves back to the Idle state.
 o  Otherwise, the system checks the PCEP session attributes
    (Keepalive frequency, DeadTimer, etc.).
 If an error is detected (e.g., malformed Open message, reception of a
 message that is not an Open message, presence of two OPEN objects),
 PCEP generates an error notification, the PCEP peer sends a PCErr
 message with Error-Type=1 and Error-value=1.  The system releases the
 PCEP resources for the PCEP peer, closes the TCP connection, and
 moves to the Idle state.

Vasseur & Le Roux Standards Track [Page 82] RFC 5440 PCEP March 2009

 If no errors are detected, OpenRetry=1, and the session
 characteristics are unacceptable, the PCEP peer sends a PCErr with
 Error-Type=1 and Error-value=5, and the system releases the PCEP
 resources for that peer and moves back 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 clears the OpenWait timer and moves to the
 UP state.
 If LocalOK=0, the system clears the OpenWait timer, starts the
 KeepWait timer, and moves to the KeepWait state.
 If no errors are detected, but the session characteristics are
 unacceptable and non-negotiable, the PCEP peer sends a PCErr with
 Error-Type=1 and Error-value=3, and the system releases the PCEP
 resources for that peer and moves back to the Idle state.
 If no errors are detected, and OpenRetry is 0, and the session
 characteristics are unacceptable but negotiable (such as, the
 Keepalive period or the DeadTimer), then the system:
 o  Increments the OpenRetry variable,
 o  Sends a PCErr message with Error-Type=1 and Error-value=4 that
    contains proposed acceptable session characteristics,
 o  If LocalOK=1, the system restarts the OpenWait timer and stays in
    the OpenWait state.
 o  If LocalOK=0, the system clears the OpenWait timer, starts the
    KeepWait timer, and moves to the KeepWait state.
 If no Open message is received before the expiration of the OpenWait
 timer, the PCEP peer sends a PCErr message with Error-Type=1 and
 Error-value=2, the system releases the PCEP resources for the PCEP
 peer, closes the TCP connection, and moves to the Idle state.
 In response to any other event, the system releases the PCEP
 resources for that peer and moves back to the Idle state.

Vasseur & Le Roux Standards Track [Page 83] RFC 5440 PCEP March 2009

 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
 characteristics proposed in the Open message.
 If an error is detected (e.g., malformed Keepalive message), PCEP
 generates an error notification, the PCEP peer sends a PCErr message
 with Error-Type=1 and Error-value=1.  The system releases the PCEP
 resources for the PCEP peer, closes the TCP connection, and moves to
 the Idle state.
 If a Keepalive message is received before the expiration of the
 KeepWait timer, then the system sets LocalOK=1 and:
 o  If RemoteOK=1, the system clears the KeepWait timer and moves to
    the UP state.
 o  If RemoteOK=0, the system clears the KeepWait timer, starts the
    OpenWait timer, and 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 PCEP peer sends a
     PCErr message with Error-Type=1 and Error-value=6, and the system
     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 system 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 restarts the
     KeepWait timer and stays in the KeepWait state.  If RemoteOK=0,
     the system clears the KeepWait timer, starts the OpenWait timer,
     and moves to the OpenWait state.
 If neither a Keepalive nor a PCErr is received after the expiration
 of the KeepWait timer, the PCEP peer sends a PCErr message with
 Error-Type=1 and Error-value=7, and the system releases the PCEP
 resources for that PCEP peer, closes the TCP connection, and moves to
 the Idle State.
 In response to any other event, the system releases the PCEP
 resources for that peer and moves back to the Idle state.

Vasseur & Le Roux Standards Track [Page 84] RFC 5440 PCEP March 2009

 UP State:
 In the UP state, the PCEP peer starts exchanging PCEP messages
 according to the session characteristics.
 If the Keepalive timer expires, the system restarts the Keepalive
 timer and sends a Keepalive message.
 If no PCEP message (Keepalive, PCReq, PCRep, PCNtf) is received from
 the PCEP peer before the expiration of the DeadTimer, the system
 terminates the PCEP session according to the procedure defined in
 Section 6.8, releases the PCEP resources for that PCEP peer, closes
 the TCP connection, and moves to the Idle State.
 If a malformed message is received, the system terminates the PCEP
 session according to the procedure defined in Section 6.8, releases
 the PCEP resources for that PCEP peer, closes the TCP connection and
 moves to the Idle State.
 If the system detects that the PCEP peer tries to set up a second TCP
 connection, it stops the TCP connection establishment and sends a
 PCErr with Error-Type=9.
 If the TCP connection fails, the system releases the PCEP resources
 for that PCEP peer, closes the TCP connection, and moves to the Idle
 State.

Appendix B. PCEP Variables

 PCEP defines the following configurable variables:
 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
    declares the session down if no PCEP message has been received.
 SyncTimer:  timer used in the case of synchronized path computation
    request using the SVEC object defined in Section 7.13.3.  Consider
    the case where a PCReq message is received by a PCE that contains
    the SVEC object referring to M synchronized path computation
    requests.  If after the expiration of the SyncTimer 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.  The aim of the SyncTimer is to avoid the
    storage of unused synchronized requests should one of them get
    lost for some reason (e.g., a misbehaving PCC).  Thus, the value

Vasseur & Le Roux Standards Track [Page 85] RFC 5440 PCEP March 2009

    of the SyncTimer must be large enough to avoid the expiration of
    the timer under normal circumstances.  A RECOMMENDED value for the
    SyncTimer is 60 seconds.
 MAX-UNKNOWN-REQUESTS:  A RECOMMENDED value is 5.
 MAX-UNKNOWN-MESSAGES:  A RECOMMENDED value is 5.

Appendix C. Contributors

 The content of this document was contributed by those listed below
 and the editors listed at the end of the document.
 Arthi Ayyangar
 Juniper Networks
 1194 N. Mathilda Ave
 Sunnyvale, CA  94089
 USA
 EMail: arthi@juniper.net
 Adrian Farrel
 Old Dog Consulting
 Phone: +44 (0) 1978 860944
 EMail: adrian@olddog.co.uk
 Eiji Oki
 NTT
 Midori 3-9-11
 Musashino, Tokyo,   180-8585
 JAPAN
 EMail: oki.eiji@lab.ntt.co.jp
 Alia Atlas
 British Telecom
 EMail: akatlas@alum.mit.edu

Vasseur & Le Roux Standards Track [Page 86] RFC 5440 PCEP March 2009

 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

Authors' Addresses

 JP Vasseur (editor)
 Cisco Systems
 1414 Massachusetts Avenue
 Boxborough, MA  01719
 USA
 EMail: jpv@cisco.com
 JL Le Roux (editor)
 France Telecom
 2, Avenue Pierre-Marzin
 Lannion  22307
 FRANCE
 EMail: jeanlouis.leroux@orange-ftgroup.com

Vasseur & Le Roux Standards Track [Page 87]

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