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RFC 5886 - A Set of Monitoring Tools for Path Computation Elemen


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Internet Engineering Task Force (IETF)                  JP. Vasseur, Ed.
Request for Comments: 5886                           Cisco Systems, Inc.
Category: Standards Track                                    JL. Le Roux
ISSN: 2070-1721                                           France Telecom
                                                              Y. Ikejiri
                                          NTT Communications Corporation
                                                               June 2010

                     A Set of Monitoring Tools for
           Path Computation Element (PCE)-Based Architecture

Abstract

   A Path Computation Element (PCE)-based architecture has been
   specified for the computation of Traffic Engineering (TE) Label
   Switched Paths (LSPs) in Multiprotocol Label Switching (MPLS) and
   Generalized MPLS (GMPLS) networks in the context of single or
   multiple domains (where a domain refers to a collection of network
   elements within a common sphere of address management or path
   computational responsibility such as Interior Gateway Protocol (IGP)
   areas and Autonomous Systems).  Path Computation Clients (PCCs) send
   computation requests to PCEs, and these may forward the requests to
   and cooperate with other PCEs forming a "path computation chain".

   In PCE-based environments, it is thus critical to monitor the state
   of the path computation chain for troubleshooting and performance
   monitoring purposes: liveness of each element (PCE) involved in the
   PCE chain and detection of potential resource contention states and
   statistics in terms of path computation times are examples of such
   metrics of interest.  This document specifies procedures and
   extensions to the Path Computation Element Protocol (PCEP) in order
   to gather such information.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc5886.

Copyright Notice

   Copyright (c) 2010 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
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1. Introduction ....................................................4
      1.1. Requirements Language ......................................5
   2. Terminology .....................................................5
   3. Path Computation Monitoring Messages ............................6
      3.1. Path Computation Monitoring Request (PCMonReq) Message .....6
      3.2. Path Monitoring Reply (PCMonRep) Message ...................9
   4. Path Computation Monitoring Objects ............................11
      4.1. MONITORING Object .........................................11
      4.2. PCC-ID-REQ Object .........................................13
      4.3. PCE-ID Object .............................................14
      4.4. PROC-TIME Object ..........................................15
      4.5. OVERLOAD Object ...........................................17
   5. Policy .........................................................18
   6. Elements of Procedure ..........................................18
   7. Manageability Considerations ...................................20
      7.1. Control of Function and Policy ............................20
      7.2. Information and Data Models ...............................20
      7.3. Liveness Detection and Monitoring .........................20
      7.4. Verify Correct Operations .................................20
      7.5. Requirements on Other Protocols ...........................21
      7.6. Impact on Network Operations ..............................21
   8. Guidelines to Avoid Overload Thrashing .........................21
   9. IANA Considerations ............................................22
      9.1. New PCEP Message ..........................................22
      9.2. New PCEP Objects ..........................................22
      9.3. New Error-Values ..........................................23
      9.4. MONITORING Object Flag Field ..............................23
      9.5. PROC-TIME Object Flag Field ...............................24
      9.6. OVERLOAD Object Flag Field ................................24
   10. Security Considerations .......................................24
   11. Acknowledgments ...............................................25
   12. References ....................................................25
      12.1. Normative References .....................................25
      12.2. Informative References ...................................25

1.  Introduction

   The Path Computation Element (PCE)-based architecture has been
   specified in [RFC4655] for the computation of Traffic Engineering
   (TE) Label Switched Paths (LSPs) in Multiprotocol Label Switching
   (MPLS) and Generalized MPLS (GMPLS) networks in the context of single
   or multiple domains where a domain refers to a collection of network
   elements within a common sphere of address management or path
   computational responsibility such Interior Gateway Protocol (IGP)
   areas and Autonomous Systems.

   Path Computation Clients (PCCs) send computation requests to PCEs
   using PCReq messages, and these may forward the requests to and
   cooperate with other PCEs forming a "path computation chain".  In the
   case of successful path computation, the computed paths are then
   provided to the requesting PCC using PCRep messages.  The PCReq and
   PCRep messages are defined in [RFC5440].

   In PCE-based environments, it is critical to monitor the state of the
   path computation chain for troubleshooting and performance monitoring
   purposes: liveness of each element (PCE) involved in the PCE chain
   and detection of potential resource contention states and statistics
   in terms of path computation times are examples of such metrics of
   interest.

   As defined in [RFC4655], there are circumstances in which more than
   one PCE is involved in the computation of a TE LSP.  A typical
   example is when the PCC requires the computation of a TE LSP where
   the head-end and the tail-end of the TE LSP do not reside in adjacent
   domains and there is no single PCE with the visibility of both the
   head-end and tail-end domain.  We call the set of PCEs involved in
   the computation of a TE LSP a "path computation chain".  As further
   discussed in Section 3.1, the path computation chain may either be
   static (pre-configured) or dynamically determined during the path
   computation process.

   As discussed in [RFC4655], a TE LSP may be computed by one PCE
   (referred to as single PCE path computation) or several PCEs
   (referred to as multiple PCE path computation).  In the former case,
   the PCC may be able to use IGP extensions to check the liveness of
   the PCE (see [RFC5088] and [RFC5089]) or PCEP using Keepalive
   messages.  In contrast, when multiple PCEs are involved in the path
   computation chain, an example of which is the Backward Recursive PCE-
   based Computation (BRPC) procedure defined in [RFC5441], the PCC's
   visibility may be limited to the first PCE involved in the path
   computation chain.  Thus, it is critical to define mechanisms in
   order to monitor the state of the path computation chain.

   This document specifies PCEP extensions in order to gather various
   state metrics along the path computation chain.  In this document, we
   call a "state metric" a metric that characterizes a PCE state.  For
   example, such a metric can have a form of a boolean (PCE is alive or
   not, PCE is congested or not) or a performance metric (path
   computation time at each PCE).

   PCE state metrics can be gathered in two different contexts: in band
   or out of band.  By "in band" we refer to the situation whereby a PCC
   requests to gather metrics in the context of a path computation
   request.  For example, a PCC may send a path computation request to a
   PCE and may want to know the processing time of that request in
   addition to the computed path.  Conversely, if the request is "out of
   band", PCE state metric collection is performed as a standalone
   request (e.g., check the liveness of a specific path computation
   chain, collect the average processing time computed over the last
   5-minute period on one or more PCEs).

   In this document, we define two monitoring request types: general and
   specific.  A general monitoring request relates to the collection of
   a PCE state metrics that is not coupled to a particular path
   computation request (e.g., average CPU load on a PCE).  Conversely, a
   specific monitoring request relates to a particular path computation
   request (processing time to complete the path computation for a TE
   LSP).

   This document specifies procedures and extensions to the Path
   Computation Element Protocol (PCEP) ([RFC5440]), including new
   objects and new PCEP messages, in order to monitor the path
   computation chain and gather various performance metrics.

   The message formats in this document are specified using Backus Naur
   Format (BNF) encoding as specified in [RFC5511].

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

   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.

   TE LSP: Traffic Engineering Label Switched Path.

3.  Path Computation Monitoring Messages

   As defined in [RFC5440], a PCEP message consists of a common header
   followed by a variable-length body made of a set of objects that can
   be either mandatory or optional.  As a reminder, an object is said to
   be mandatory in a PCEP message when the object must be included for
   the message to be considered valid.  The P flag (defined in
   [RFC5440]) is located in the common header of each PCEP object and
   can be set by a PCEP peer to require a PCE to take into account the
   related information during the path computation.  Because the P flag
   exclusively relates to a path computation request, it MUST be cleared
   in the two PCEP messages (PCMonReq and PCMonRep message) defined in
   this document.

   For each PCEP message type, a set of rules is defined that specify
   the set of objects that the message can carry.  An implementation
   MUST form the PCEP messages using the object ordering specified in
   this document.

   In this document, we define two PCEP messages referred to as the Path
   Computation Monitoring Request (PCMonReq) and Path Computation
   Monitoring Reply (PCMonRep) messages so as to handle out-of-band
   monitoring requests.  The aim of the PCMonReq message sent by a PCC
   to a PCE is to gather one or more PCE state metrics on a set of PCEs
   involved in a path computation chain.  The PCMonRep message sent by a
   PCE to a PCC is used to provide such data.

3.1.  Path Computation Monitoring Request (PCMonReq) Message

   The Message-Type field of the PCEP common header for the PCMonReq
   message is set to 8.

   There is one mandatory object that MUST be included within a PCMonReq
   message: the MONITORING object (see Section 4.1).  If the MONITORING
   object is missing, the receiving PCE MUST send a PCErr message with
   Error-type=6 (Mandatory Object missing) and Error-value=4 (MONITORING
   object missing).  Other objects are optional.

   Format of a PCMonReq message (out-of-band request):
   <PCMonReq Message>::= <Common Header>
                         <MONITORING>
                         <PCC-ID-REQ>
                         [<pce-list>]
                         [<svec-list>]
                         [<request-list>]

   where:

   <pce-list>::=<PCE-ID>[<pce-list>]

   <svec-list>::=<SVEC>
                 [<OF>]
                 [<svec-list>]

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

   <request>::= <RP>
                <END-POINTS>
                [<LSPA>]
                [<BANDWIDTH>]
                [<metric-list>]
                [<RRO>]
                [<IRO>]
                [<LOAD-BALANCING>]
                [<XRO>]

   <metric-list>::=<METRIC>[<metric-list>]

   Format of a PCReq message with monitoring data requested (in-band
   request):
   <PCReq Message>::= <Common Header>
                      <MONITORING>
                      <PCC-ID-REQ>
                      [<pce-list>]
                      [<svec-list>]
                      <request-list>

   where:

      <pce-list>::=<PCE-ID>[<pce-list>]

      <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 [RFC5440].  The XRO object is
   defined in [RFC5521] and the OF object is defined in [RFC5541].  The
   PCC-ID-REQ object is defined in Section 4.2.

   The PCMonReq message is used to gather various PCE state metrics
   along a path computation chain.  The path computation chain may be
   determined by the PCC (in the form of a series of a series of PCE-ID
   objects defined in Section 4.3) according to policy specified on the
   PCC or alternatively may be determined by the path computation
   procedure.  For example, if the BRPC procedure ([RFC5441]) is used to
   compute an inter-domain TE LSP, the path computation chain may be
   determined dynamically.  In that case, the PCC sends a PCMonReq
   message that contains the PCEP objects that characterize the TE LSP
   attributes along with the MONITORING object (see Section 4.1) that
   lists the set of metrics of interest.  If a list of PCEs is present
   in the monitoring request, it takes precedence over mechanisms used
   to dynamically determine the path computation chain.  If a PCE
   receives a monitoring request that specifies a next-hop PCE in the
   PCE list that is unreachable, the request MUST be silently discarded.

   Several PCE state metrics may be requested that are specified by a
   set of objects defined in Section 4.  Note that this set of objects
   may be extended in the future.

   As pointed out in [RFC5440], several situations can arise in the form
   of:

   o  a bundle of a set of independent and non-synchronized path
      computation requests,

   o  a bundle of a set of independent and synchronized path computation
      requests (SVEC object defined below required), or

   o  a bundle of a set of dependent and synchronized path computation
      requests (SVEC object defined below required).

   In the case of a bundle of a set of requests, the MONITORING object
   SHOULD only be present in the first PCReq or PCMonReq message, and
   the monitoring request applies to all the requests of the bundle,
   even in the case of dependent and/or synchronized requests sent using
   more than one PCReq or PCMonReq message.

   Examples of requests.  For the sake of illustration, consider the
   three following examples:

   Example 1 (out-of-band request): PCC1 makes a request to check the
   path computation chain that would be used should it request a path
   computation for a specific TE LSP named T1.  A PCMonReq message is
   sent that contains a MONITORING object specifying a path computation
   check, along with the appropriate set of objects (e.g., RP, END-
   POINTS, etc.) that would be included in a PCReq message for T1.

   Example 2 (in-band request): PCC1 requests a path computation for a
   TE LSP and also makes a request to gather the processing time along
   the path computation chain selected for the computation of T1.  A
   PCReq message is sent that also contains a MONITORING object that
   specifies the performance metrics of interest.

   Example 3 (out-of-band request): PCC2 requests to gather performance
   metrics along the specific path computation chain <pce1, pce2, pce3,
   pce7>.  A PCMonReq message is sent to PCE1 that contains a MONITORING
   object and a sequence of PCE-ID objects that identify PCE1, PCE2,
   PCE3, and PCE7, respectively.

   In all of the examples above, a PCRep message (in-band request) or
   PCMonReq message (out-of-band request) is sent in response to the
   request that reports the computed metrics.

3.2.  Path Monitoring Reply (PCMonRep) Message

   The PCMonRep message is used to provide PCE state metrics back to the
   requester for out-of-band monitoring requests.  The Message-Type
   field of the PCEP common header for the PCMonRep message is set to 9.

   There is one mandatory object that MUST be included within a PCMonRep
   message: the MONITORING object (see Section 4.1).  If the MONITORING
   object is missing, the receiving PCE MUST send a PCErr message with
   Error-type=6 (Mandatory Object missing) and Error-value=4 (MONITORING
   object missing).

   Other objects are optional.

   Format of a PCMonRep (out-of-band request):
   <PCMonRep Message>::= <Common Header>
                         <MONITORING>
                         <PCC-ID-REQ>
                         [<RP>]
                         [<metric-pce-list>]

   where:

   <metric-pce-list>::=<metric-pce>[<metric-pce-list>]

   <metric-pce>::=<PCE-ID>
                  [<PROC-TIME>]
                  [<OVERLOAD>]

   Format of a PCRep message with monitoring data (in band):
   <PCRep Message> ::= <Common Header>
                       <response-list>

   where:

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

      <response>::=<RP>
                   <MONITORING>
                   <PCC-ID-REQ>
                  [<NO-PATH>]
                  [<attribute-list>]
                  [<path-list>]
                  [<metric-pce-list>]

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

      <path>::= <ERO><attribute-list>

   where:

    <attribute-list>::=[<LSPA>]
                       [<BANDWIDTH>]
                       [<metric-list>]
                       [<IRO>]

    <metric-list>::=<METRIC>[<metric-list>]

    <metric-pce-list>::=<metric-pce>[<metric-pce-list>]

    <metric-pce>::=<PCE-ID>
                  [<PROC-TIME>]
                  [<OVERLOAD>]

   The RP and the NO-PATH objects are defined in [RFC5440].  The PCC-ID-
   REQ object is defined in Section 4.2.

   If the path computation chain has been statically specified in the
   corresponding monitoring request using the series of a series of PCE-
   ID objects defined in Section 4.3, the monitoring request MUST use
   the same path computation chain (using the PCE list but in the
   reverse order).

4.  Path Computation Monitoring Objects

   The PCEP objects defined in the document are compliant with the PCEP
   object format defined in [RFC5440].  The P flag and the I flag of the
   PCEP objects defined in this document SHOULD always be set to 0 on
   transmission and MUST be ignored on receipt since these flags are
   exclusively related to path computation requests.

   Several objects are defined in this section that can be carried
   within the PCEP PCReq or PCRep messages defined in [RFC5440] in the
   case of in-band monitoring requests (the PCC requests the computation
   of the TE LSP in addition to gathering PCE state metrics).  In the
   case of out-of-band monitoring requests, the objects defined in this
   section are carried within PCMonReq and PCMonRep messages.

   All TLVs carried in objects defined in this document have the TLV
   format defined in [RFC5440]:

   o  Type: 2 bytes

   o  Length: 2 bytes

   o  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-byte 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.

4.1.  MONITORING Object

   The MONITORING object MUST be present within PCMonReq and PCMonRep
   messages (out-of-band monitoring requests) and MAY be carried within
   PCRep and PCReq messages (in-band monitoring requests).  There SHOULD
   NOT be more than one instance of the MONITORING object in a PCMonReq
   or PCMonRep message: if more than one instance of the MONITORING
   object is present, the recipient MUST process the first instance and
   MUST ignore other instances.

   The MONITORING object is used to specify the set of requested PCE
   state metrics.

   The MONITORING Object-Class (19) has been assigned by IANA.

   The MONITORING Object-Type (1) has been assigned by IANA.

   The format of the MONITORING 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              |I|C|P|G|L|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Monitoring-id-number                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   //                      Optional TLV(s)                        //
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Flags: 24 bits

   The following flags are currently defined:

   L (Liveness) - 1 bit: when set, this indicates that the state metric
   of interest is the PCE's liveness and thus the PCE MUST include a
   PCE-ID object in the corresponding reply.  The L bit MUST always be
   ignored in a PCMonRep or PCRep message.

   G (General) - 1 bit: when set, this indicates that the monitoring
   request is a general monitoring request.  When the requested
   performance metric is specific, the G bit MUST be cleared.  The G bit
   MUST always be ignored in a PCMonRep or PCRep message.

   P (Processing Time) - 1 bit: the P bit of the MONITORING object
   carried in a PCMonReq or a PCReq message is set to indicate that the
   processing times is a metric of interest.  If allowed by policy, a
   PROC-TIME object MUST be inserted in the corresponding PCMonRep or
   PCRep message.  The P bit MUST always be ignored in a PCMonRep or
   PCRep message.

   C (Overload) - 1 bit: The C bit of the MONITORING object carried in a
   PCMonReq or a PCReq message is set to indicate that the overload
   status is a metric of interest, in which case an OVERLOAD object MUST
   be inserted in the corresponding PCMonRep or PCRep message.  The C
   bit MUST always be ignored in a PCMonRep or PCRep message.

   I (Incomplete) - 1 bit: If a PCE supports a received PCMonReq message
   and that message does not trigger any policy violation, but the PCE
   cannot provide any of the set of requested performance metrics for
   unspecified reasons, the PCE MUST set the I bit.  The I bit has no
   meaning in a request and SHOULD be ignored on receipt.

   Monitoring-id-number (32 bits): The monitoring-id-number value
   combined with the PCC-REQ-ID identifying the requesting PCC uniquely
   identifies the monitoring request context.  The monitoring-id-number
   MUST start at a non-zero value and MUST be incremented each time a
   new monitoring request is sent to a PCE.  Each increment SHOULD have
   a value of 1 and may cause a wrap back to zero.  If no reply to a
   monitoring request is received from the PCE, and the PCC wishes to
   resend its path computation monitoring request, the same monitoring-
   id-number MUST be used.  Conversely, a different monitoring-id-number
   MUST be used for different requests sent to a PCE.  A PCEP
   implementation SHOULD checkpoint the Monitoring-id-number of pending
   monitoring requests in case of restart thus avoiding the reuse of a
   Monitoring-id-number of an in-process monitoring request.

   Unassigned bits are considered as reserved and MUST be set to zero on
   transmission and ignored on reception.

   No optional TLVs are currently defined.

4.2.  PCC-ID-REQ Object

   The PCC-ID-REQ object is used to specify the IP address of the
   requesting PCC.

   The PCC-ID-REQ MUST be inserted within a PCReq or a PCMonReq message
   to specify the IP address of the requesting PCC.

   Two PCC-ID-REQ objects (for IPv4 and IPv6) are defined.  PCC-ID-REQ
   Object-Class (20) has been assigned by IANA.  PCC-ID-REQ Object-Type
   (1 for IPv4 and 2 for IPv6) has been assigned by IANA.

   The format of the PCC-ID-REQ object body for IPv4 and IPv6 are as
   follows:

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

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   |                           IPv6 Address                        |
   |                                                               |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The PCC-ID-REQ object body has a fixed length of 4 octets for IPv4
   and 16 octets for IPv6.

4.3.  PCE-ID Object

   The PCE-ID object is used to specify a PCE's IP address.  The PCE-ID
   object can either be used to specify the list of PCEs for which
   monitoring data is requested and to specify the IP address of the
   requesting PCC.

   A set of PCE-ID objects may be inserted within a PCReq or a PCMonReq
   message to specify the PCE for which PCE state metrics are requested
   and in a PCMonRep or a PCRep message to record the IP address of the
   PCE reporting PCE state metrics or that was involved in the path
   computation chain.

   Two PCE-ID objects (for IPv4 and IPv6) are defined.  PCE-ID Object-
   Class (25) has been assigned by IANA.  PCE-ID Object-Type (1 for IPv4
   and 2 for IPv6) has been assigned by IANA.

   The format of the PCE-ID object body for IPv4 and IPv6 are as
   follows:

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

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   |                           IPv6 Address                        |
   |                                                               |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The PCE-ID object body has a fixed length of 4 octets for IPv4 and 16
   octets for IPv6.

   When a dynamic discovery mechanism is used for PCE discovery, a PCE
   advertises its PCE address in the PCE-ADDRESS sub-TLV defined in
   [RFC5088] and [RFC5089].  A PCC MUST use this address in PCReq and
   PCMonReq messages and a PCE MUST also use this address in PCRep and
   PCMonRep messages.

4.4.  PROC-TIME Object

   If allowed by policy, the PCE includes a PROC-TIME object within a
   PCMonRep or a PCRep message if the P bit of the MONITORING object
   carried within the corresponding PCMonReq or PCReq message is set.
   The PROC-TIME object is used to report various processing time
   related metrics.

   1) Case of general monitoring requests

      A PCC may request processing time metrics for general monitoring
      requests (e.g., the PCC may want to know the minimum, maximum, and
      average processing times on a particular PCE).  In this case,
      general requests can only be made by using PCMonReq/PCMonRep
      messages.  The Current-processing-time field (as explained below)
      is exclusively used for specific monitoring requests and MUST be
      cleared for general monitoring requests.  The algorithms used by a
      PCE to compute the minimum, maximum, average, and variance of the
      processing times are out of the scope of this document (a PCE may
      decide to compute the minimum processing time over a period of
      time, for the last N path computation requests, etc.).

   2) Case of specific monitoring requests

      In the case of a specific request, the algorithms used by a PCE to
      compute the Processing-time metrics are out of the scope of this
      document, but a flag is specified that is used to indicate to the
      requester whether the processing time value was estimated or
      computed.  The PCE may either (1) estimate the processing time
      without performing an actual path computation or (2) effectively
      perform the computation to report the processing time.  In the
      former case, the E bit of the PROC-TIME object MUST be set.  The G
      bit MUST be cleared and the Min-processing-time, Max-processing-
      time, Average-processing-time, and Variance-processing-time MUST
      be set to 0x00000000.

      When the processing time is requested in addition to a path
      computation (case where the MONITORING object is carried within a
      PCReq message), the PROC-TIME object always reports the actual
      processing time for that request and thus the E bit MUST be
      cleared.

   The PROC-TIME Object-Class (26) has been assigned by IANA.

   The PROC-TIME Object-Type (1) has been assigned by IANA.

   The format of the PROC-TIME 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             |E|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Current-processing-time                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Min-processing-time                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Max-processing-time                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Average-processing time                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Variance-processing-time                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Flags: 16 bits - one flag is currently defined:

   E (Estimated) - 1 bit: when set, this indicates that the reported
   metric value is based on estimated processing time as opposed to
   actual computations.

   Unassigned bits are considered as reserved and MUST be set to zero on
   transmission.

   Current-processing-time: This field indicates, in milliseconds, the
   processing time for the path computation of interest characterized in
   the corresponding PCMonReq message.

   Min-processing-time: This field indicates, in milliseconds, the
   minimum processing time.

   Max-processing-time: This field indicates, in milliseconds, the
   maximum processing time.

   Average-processing-time: This field indicates, in milliseconds, the
   average processing time.

   Variance-processing-time: This field indicates, in milliseconds, the
   variance of the processing times.

   Since the PCC may potentially use monitoring metrics as input to
   their PCE selection, it MAY be required to normalize how time metrics
   (along with others metrics described in further revision of this
   document) are computed to ensure consistency between the monitoring
   metrics computed by a set of PCEs.

4.5.  OVERLOAD Object

   The OVERLOAD object is used to report a PCE processing congestion
   state.  Note that "overload" as indicated by this object refers to
   the processing state of the PCE and its ability to handle new PCEP
   requests.  A PCE is overloaded when it has a backlog of PCEP requests
   such that it cannot immediately start to process a new request thus
   leading to waiting times.  The overload duration is quantified as
   being the (estimated) time until the PCE expects to be able to
   immediately process a new PCEP request.

   The OVERLOAD object MUST be present within a PCMonRep or a PCRep
   message if the C bit of the MONITORING object carried within the
   corresponding PCMonReq or PCReq message is set and the PCE is
   experiencing a congested state.  The OVERLOAD Object-Class (27) has
   been assigned by IANA.  The overload Object-Type (1) has been
   assigned by IANA.

   The format of the CONGESTION 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       |   Reserved    |      Overload Duration        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Flags: 8 bits - No flag is currently defined.

   Overload duration - 16 bits: This field indicates the amount of time,
   in seconds, that the responding PCE expects that it may continue to
   be overloaded from the time that the response message was generated.
   The receiver MAY use this value to decide whether or not to send
   further requests to the same PCE.

   It is worth noting that a PCE along a path computation chain involved
   in the monitoring request may decide to learn from the overload
   information received by one of downstream PCEs in the chain.

5.  Policy

   The receipt of a PCMonReq message may trigger a policy violation on
   some PCE; in which case, the PCE MUST send a PCErr message with
   Error-type=5 and Error-value=6.

6.  Elements of Procedure

   I bit processing: as indicated in Section 4.1, if a PCE supports a
   received PCMonReq message and that message does not trigger any
   policy violation, but the PCE cannot provide any of the set of
   requested performance metrics for unspecified reasons, the PCE MUST
   set the I bit.  Once set, the I bit MUST NOT be changed by a
   receiving PCE.

   Upon receiving a PCMonReq message:

   1) As specified in [RFC5440], if the PCE does not support the
      PCMonReq message, the PCE peer MUST send a PCErr message with
      Error-value=2 (capability not supported).  According to the
      procedure defined in Section 6.9 of [RFC5440], if a PCC/PCE
      receives unrecognized messages at a rate equal of greater than
      specified rate, the PCC/PCE must send a PCEP CLOSE message with
      close value=5 "Reception of an unacceptable number of unrecognized
      PCEP messages".  In this case, the PCC/PCE must also close the TCP
      session and must not send any further PCEP messages on the PCEP
      session.

   2) If the PCE supports the PCMonReq message but the monitoring
      request is prohibited by policy, the PCE must follow the procedure
      specified in Section 5.  As pointed out in Section 4.3, a PCE may
      still partially satisfy a request, leaving out some of the
      required data if not allowed by policy.

   3) If the PCE supports the PCMonReq and the monitoring request is not
      prohibited by policy, the receiving PCE MUST first determine
      whether it is the last PCE of the path computation chain.  If the
      PCE is not the last element of the path computation chain, the
      PCMonReq message is relayed to the next-hop PCE: such a next hop
      may be either specified by means of a PCE-ID object present in the
      PCMonReq message or dynamically determined by means of a procedure
      outside of the scope of this document.  Conversely, if the PCE is
      the last PCE of the path computation chain, the PCE originates a
      PCMonRep message that contains the requested objects according to
      the set of requested PCE states metrics listed in the MONITORING
      object carried in the corresponding PCMonReq message.

   Upon receiving a PCReq message that carries a MONITORING and
   potentially other monitoring objects (e.g., PCE-ID object):

   1) As specified in [RFC5440], if the PCE does not support (in-band)
      monitoring, the PCE peer MUST send a PCErr message with Error-
      value=2 (capability not supported).  According to the procedure
      defined in Section 6.9 of [RFC5440], if a PCC/PCE receives
      unrecognized messages at a rate equal or greater than a specified
      rate, the PCC/PCE must send a PCEP CLOSE message with close
      value=5 "Reception of an unacceptable number of unrecognized PCEP
      messages".  In this case, the PCC/PCE must also close the TCP
      session and must not send any further PCEP messages on the PCEP
      session.

   2) If the PCE supports the monitoring request but the monitoring
      request is prohibited by policy, the PCE must follow the procedure
      specified in Section 5.  As pointed out in Section 4.3, a PCE may
      still partially satisfy a request, leaving out some of the
      required data if not allowed by policy.

   3) If the PCE supports the monitoring request and that request is not
      prohibited by policy, the receiving PCE MUST first determine
      whether it is the last PCE of the path computation chain.  If the
      PCE is not the last element of the path computation chain, the
      PCReq message (with the MONITORING object and potentially other
      monitoring objects such as the PCE-ID) is relayed to the next-hop
      PCE: such a next hop may be either specified by means of a PCE-ID
      object present in the PCReq message or dynamically determined by
      means of a procedure outside of the scope of this document.

      Conversely, if the PCE is the last PCE of the path computation
      chain, the PCE originates a PCRep message that contains the
      requested objects according to the set of requested PCE states
      metrics listed in the MONITORING and potentially other monitoring
      objects carried in the corresponding PCReq message.

   Upon receiving a PCMonRep message, the PCE processes the request,
   adds the relevant objects to the PCMonRep message and forwards the
   PCMonRep message to the upstream requesting PCE or PCC.

   Upon receiving a PCRep message that carries monitoring data, the
   message is processed, additional monitoring data is added according
   to this specification, and the message is forwarded upstream to the
   requesting PCE or PCC.

7.  Manageability Considerations

7.1.  Control of Function and Policy

   It MUST be possible to configure the activation/deactivation of PCEP
   monitoring on a PCEP speaker.  In addition to the parameters already
   listed in Section 8.1 of [RFC5440], a PCEP implementation SHOULD
   allow configuring on a PCE whether or not specific, generic, in-band
   and out-of-band monitoring requests are allowed.  Also, a PCEP
   implementation SHOULD allow configuring on a PCE a list of authorized
   state metrics (aliveness, overload, processing time, etc.).  This may
   apply to any session in which the PCEP speaker participates, to a
   specific session with a given PCEP peer or to a specific group of
   sessions with a specific group of PCEP peers, for instance, the PCEP
   peers of a neighbor AS.

7.2.  Information and Data Models

   A new MIB Module may be defined that provides local PCE state
   metrics, as well as state metrics of other PCEs gathered using
   mechanisms defined in this document.

7.3.  Liveness Detection and Monitoring

   This document provides mechanisms to monitor the liveliness and
   performances of a given path computation chain.

7.4.  Verify Correct Operations

   Mechanisms defined in this document do not imply any new operation
   verification requirements in addition to those already listed in
   [RFC5440].

7.5.  Requirements on Other Protocols

   Mechanisms defined in this document do not imply any requirements on
   other protocols in addition to those already listed in [RFC5440].

7.6.  Impact on Network Operations

   The frequency of PCMonReq messages may impact the operations of PCEs.
   An implementation SHOULD allow a limit to be placed on the rate of
   PCMonReq messages sent by a PCEP speaker and processed from a peer.
   It SHOULD also allow sending a notification when a rate threshold is
   reached.  An implementation SHOULD allow handling PCReq messages with
   a higher priority than PCMonReq messages.  An implementation SHOULD
   allow the configuration of a second limit for the PCReq message
   requesting monitoring data.

8.  Guidelines to Avoid Overload Thrashing

   An important concern while processing overload information is to
   prevent the overload condition on one PCE simply being moved to
   another PCE.  Indeed, there is a risk that the reaction to an
   indication of overload will act to increase the amount of overload
   within the network.  Furthermore, this may lead to oscillations
   between PCEs if the overload information is not handled properly.

   This section presents some brief guidance on how a PCC (which term
   includes a PCE making requests of another PCE) should react when it
   receives an indication that a PCE is overloaded.

   When an overload indication is received (on a PCRep message or on a
   PCMonRep message), it identifies that new PCReq messages sent to the
   PCE might be subject to a delay equal to the value in the Overload
   Duration field (when present).

   It also indicates that PCReq messages already queued at the PCE might
   be subject to a delay.  The PCC must decide how to handle new PCReq
   messages and what to do about PCReq messages already queued at the
   PCE.

   It is RECOMMENDED that a PCC does not cancel a queued PCReq and
   reissue it to another PCE because of the PCE being overloaded.

   Such behavior is likely to result in overload thrashing as multiple
   PCCs move the PCE queue to another PCE.  This would simply introduce
   additional delay in the processing of all requests.  A PCC MAY choose
   to cancel a queued PCE request if it is willing to sacrifice the
   request, maybe reissuing it later (after the overload condition has
   been determined to have cleared by use of a PCMonReq/Rep exchange).

   It is then RECOMMENDED to send the cancellation request with a higher
   priority in order for the overloaded PCE to detect the request
   cancellation before processing the related request.

   A PCC that is aware of PCE overload at one PCE MAY select a different
   PCE to service its next PCReq message.  In doing so, it is
   RECOMMENDED that the PCC consider whether the other PCE is overloaded
   or might be likely to become overloaded by other PCCs similarly
   directing new PCReq messages.

   Furthermore, should the second PCE be also overloaded, it is
   RECOMMENDED not to make any attempt to switch back to the other PCE
   without knowing that the first PCE is no longer overloaded.

9.  IANA Considerations

9.1.  New PCEP Message

   Each PCEP message has a message type value.

   Two new PCEP (specified in [RFC5440]) messages are defined in this
   document:

   Value  Description                                      Reference
     8    Path Computation Monitoring Request (PCMonReq)   This document
     9    Path Computation Monitoring Reply (PCMonRep)     This document

9.2.  New PCEP Objects

   Each PCEP object has an Object-Class and an Object-Type.  The
   following new PCEP objects are defined in this document:

   Object-Class Value Name        Object-Type             Reference

          19          MONITORING  1                       This document

          20          PCC-REQ-ID  1: IPv4 addresses       This document
                                  2: IPv6 addresses

          25          PCE-ID      1: IPv4 addresses       This document
                                  2: IPv6 addresses       This document

          26          PROC-TIME   1                       This document

          27          OVERLOAD    1: overload             This document

9.3.  New Error-Values

   A registry was created for the Error-type and Error-value of the PCEP
   Error Object.

   A new Error-value for the PCErr message Error-type=5 (Policy
   Violation) (see [RFC5440]) is defined in this document.

   Error-type  Meaning           Error-value             Reference

      5        Policy violation  6: Monitoring message   This document
                                 supported but rejected
                                 due to policy violation

   A new Error-value for the PCErr message Error-type=6 (Mandatory
   object missing) (see [RFC5440]) is defined in this document.

   Error-type  Meaning           Error-value             Reference

      6        Mandatory Object  4: MONITORING object    This document
               missing           missing

9.4.  MONITORING Object Flag Field

   IANA has created a registry to manage the Flag field of
   the MONITORING object.

   New bit numbers may be allocated only by an IETF Review.  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 for the MONITORING Object flag field in this
   document:

   Codespace of the Flag field (MONITORING Object)
    Bit      Description         Reference
   0-18      Unassigned
     19      Incomplete          This document
     20      Overload            This document
     21      Processing Time     This document
     22      General             This document
     23      Liveness            This document

9.5.  PROC-TIME Object Flag Field

   IANA has created a registry to manage the Flag field of the PROC-TIME
   object.

   New bit numbers may be allocated only by an IETF Review.  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 PROC-TIME Object flag field in this
   document:

   Codespace of the Flag field (PROC-TIME Object)
    Bit      Description             Reference
   0-14      Unassigned
     15      Estimated               This document

9.6.  OVERLOAD Object Flag Field

   IANA has created a registry to manage the Flag field of the OVERLOAD
   object.

   New bit numbers may be allocated only by an IETF Review.  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 Flag is currently defined for the OVERLOAD Object flag field in
   this document.

   Codespace of the Flag field (OVERLOAD Object)
     Bit      Description             Reference
     0-7      Unassigned

10.  Security Considerations

   The use of monitoring data can be used for various attacks such as
   denial-of-service (DoS) attacks (for example, by setting the C bit
   and overload duration field of the OVERLOAD object to stop PCCs from

   using a PCE).  Thus, it is recommended to make use of the security
   mechanisms discussed in [RFC5440] to secure a PCEP session
   (authenticity, integrity, privacy, and DoS protection, etc.) to
   secure the PCMonReq and PCMonRep messages and PCE state metric
   objects defined in this document.  An implementation SHOULD allow
   limiting the rate at which PCMonReq or PCReq messages carrying
   monitoring requests received from a specific peer are processed
   (input shaping) as discussed in Section 10.7.2 of [RFC5440], or from
   another domain (see also Section 7.6).

11.  Acknowledgments

   The authors would like to thank Eiji Oki, Mach Chen, Fabien
   Verhaeghe, Dimitri Papadimitriou, and Francis Dupont for their useful
   comments.  Special thanks to Adrian Farrel for his detailed 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.

   [RFC5440]  Vasseur, JP., Ed., and JL. Le Roux, Ed., "Path Computation
              Element (PCE) Communication Protocol (PCEP)", RFC 5440,
              March 2009.

   [RFC5511]  Farrel, A., "Routing Backus-Naur Form (RBNF): A Syntax
              Used to Form Encoding Rules in Various Routing Protocol
              Specifications", RFC 5511, April 2009.

   [RFC5521]  Oki, E., Takeda, T., and A. Farrel, "Extensions to the
              Path Computation Element Communication Protocol (PCEP) for
              Route Exclusions", RFC 5521, April 2009.

   [RFC5541]  Le Roux, JL., Vasseur, JP., and Y. Lee, "Encoding of
              Objective Functions in the Path Computation Element
              Communication Protocol (PCEP)", RFC 5541, June 2009.

12.2.  Informative References

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

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

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

   [RFC5441]  Vasseur, JP., Ed., Zhang, R., Bitar, N., and JL. Le Roux,
              "A Backward-Recursive PCE-Based Computation (BRPC)
              Procedure to Compute Shortest Constrained Inter-Domain
              Traffic Engineering Label Switched Paths", RFC 5441, April
              2009.

Authors' Addresses

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

   EMail: jpv@cisco.com

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

   EMail: jeanlouis.leroux@orange-ftgroup.com

   Yuichi Ikejiri
   NTT Communications Corporation
   1-1-6, Uchisaiwai-cho, Chiyoda-ku
   Tokyo 100-8019
   Japan

   EMail: y.ikejiri@ntt.com

 

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