PCE Working Group                                       Xian Zhang
Internet-Draft                                                Young Lee
Intended status: Standards Track                            Fatai Zhang
                                                          Ramon Casellas
                                                  Oscar Gonzalez de Dios
                                                         Telefonica I+D
                                                               Zafar Ali
                                                           Cisco Systems

Expires: November 11, 2017                       May 11, 2017

  Path Computation Element (PCE) Protocol Extensions for Stateful PCE
                   Usage in GMPLS-controlled Networks



   The Path Computation Element (PCE) facilitates Traffic Engineering
   (TE) based path calculation in large, multi-domain, multi-region, or
   multi-layer networks. The PCE communication Protocol (PCEP) has been
   extended to support stateful PCE functions where the PCE retains
   information about the paths already present in the network, but
   those extensions are technology-agnostic. This memo provides
   extensions required for PCEP so as to enable the usage of a stateful
   PCE capability in GMPLS-controlled networks.

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with
   the provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-

   Internet-Drafts are draft documents valid for a maximum of six
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   documents at any   time.  It is inappropriate to use Internet-Drafts

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   as reference   material or to cite them other than as "work in

   The list of current Internet-Drafts can be accessed at

   The list of Internet-Draft Shadow Directories can be accessed at

   This Internet-Draft will expire on November 11, 2017.

Copyright Notice

   Copyright (c) 2017 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
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   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document. Please review these documents
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   document must include Simplified BSD License text as described in
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   warranty as described in the Simplified BSD License.

Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC-2119 [RFC2119].

Table of Contents

   Table of Contents.................................................2
   1. Introduction...................................................3
   2. PCEP Extensions................................................3
      2.1. Overview of Requirements..................................3
      2.2. LSP Delegation in GMPLS-controlled Networks...............4
      2.3. LSP Synchronization in GMPLS-controlled Networks..........5
      2.4. Modification of Existing PCEP Messages and Procedures.....6
         2.4.1. Modification for LSP Re-optimization.................6
         2.4.2. Modification for Route Exclusion.....................7
      2.5. Object Encoding...........................................8
   3. IANA Considerations............................................8

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      3.1. New PCEP Error Codes......................................8
      3.2. New Subobject for the Exclude Route Object................9
   4. Manageability Considerations...................................9
      4.1. Requirements on Other Protocols and Functional Components.9
   5. Security Considerations........................................9
   6. Acknowledgement...............................................10
   7. References....................................................10
      7.1. Normative References.....................................10
      7.2. Informative References...................................10
   8. Contributors' Address.........................................11
   Authors' Addresses...............................................12

1. Introduction

   [RFC4655] presents the architecture of a Path Computation Element
   (PCE)-based model for computing Multiprotocol Label Switching (MPLS)
   and Generalized MPLS (GMPLS) Traffic Engineering Label Switched
   Paths (TE LSPs).  To perform such a constrained computation, a PCE
   stores the network topology (i.e., TE links and nodes) and resource
   information (i.e., TE attributes) in its TE Database (TED).  Such a
   PCE is usually referred as a stateless PCE. To request path
   computation services to a PCE, [RFC5440] defines the PCE
   communication Protocol (PCEP) for interaction between a Path
   Computation Client (PCC) and a PCE, or between two PCEs.  PCEP as
   specified in [RFC 5440] mainly focuses on MPLS networks and the PCEP
   extensions needed for GMPLS-controlled networks are provided in

   Stateful PCEs are shown to be helpful in many application scenarios,
   in both MPLS and GMPLS networks, as illustrated in [RFC8051].
   Further discussion of concept of a stateful PCE can be found in
   [RFC7399].  In order for these applications to able to exploit the
   capability of stateful PCEs, extensions to PCEP are required.

   [Stateful-PCE] provides the fundamental extensions needed for
   stateful PCE to support general functionality, but leaves out the
   specification for technology-specific objects/TLVs. This document
   focuses on the extensions that are necessary in order for the
   deployment of stateful PCEs in GMPLS-controlled networks.

2. PCEP Extensions

2.1. Overview of Requirements

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   This section notes the main functional requirements for PCEP
   extensions to support stateful PCE for use in GMPLS-controlled
   networks, based on the description in [RFC8051].  Many
   requirements are common across a variety of network types (e.g.,
   MPLS-TE networks and GMPLS networks) and the protocol extensions to
   meet the requirements are already described in [Stateful-PCE].  This
   document does not repeat the description of those protocol
   extensions.  This document presents protocol extensions for a set of
   requirements which are specific to the use of a stateful PCE in a
   GMPLS-controlled network.

   The basic requirements are as follows:

  o  Advertisement of the stateful PCE capability.  This generic
     requirement is covered in Section 5.4. of [Stateful-PCE].  This
     document does not provide any further extensions.

  o  LSP delegation is already covered in Section 5.5. of [Stateful-
     PCE].  Section 2.3. of this document provides extension for its
     application in GMPLS-controlled networks.  Moreover, further
     discussion of some generic details that need additional
     consideration is provided.

  o  LSP state synchronization and LSP state report. This is a generic
     requirement already covered in Section 5.6. of [Stateful-PCE].
     However, there are further extensions required specifically for
     GMPLS-controlled networks and discussed in Section 2.4.  Reference
     to LSPs by identifiers is discussed in Section 5.6. of [Stateful-
     PCE].  This feature can be applied to reduce the data carried in
     PCEP messages.  Use cases and additional Error Codes are necessary,
     as described in Section 2.5. of this document.

2.2. LSP Delegation in GMPLS-controlled Networks

   [Stateful-PCE] defines the Path Computation LSP Update Request
   (PCUpd) message to enable to update the attributes of an LSP.
   However, that document does not define technology-specific

   A key element of the PCUpd message is the attribute-list construct
   defined in [RFC5440] and extended by many other PCEP specifications.

   For GMPLS purposes we note that the BANDWIDTH object used in the
   attribute-list is defined in [PCEP-GMPLS].  Furthermore, additional
   TLVs are defined for the LSPA object in [PCEP-GMPLS] and MAY be
   included to indicate technology-specific attributes.

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   LSP parameter update controlled by a stateful PCE in a multi-domain
   network is complex and requires well-defined operational procedures
   as well as protocol design and is out of scope of this document and
   left for further study.

2.3. LSP Synchronization in GMPLS-controlled Networks

   PCCs need to report the attributes of LSPs to the PCE to enable
   stateful operation of a GMPLS network.  This process is known as
   LSP state synchronization.  The LSP attributes include bandwidth,
   associated route, and protection information etc., are stored by the
   PCE in the LSP database (LSP-DB).  Note that, as described in
   [Stateful-PCE], the LSP state synchronization covers both the bulk
   reporting of LSPs at initialization as well the reporting of new or
   modified LSP during normal operation. Incremental LSP-DB
   synchronization may be desired in a GMPLS-controlled network and it
   is specified in [Sync-OPT].

   [Stateful-PCE] describes mechanisms for LSP synchronization using
   the Path Computation State Report (PCRpt) message, but does not
   cover reporting of technology-specific attributes. As stated in
   [Stateful-PCE], the <path> construct is further composed of a
   compulsory ERO object and a compulsory attribute-list and an
   optional RRO object. In order to report LSP states in GMPLS networks,
   this specification allows the use within a PCRpt message both of
   technology- and GMPLS-specific attribute objects and TLVs defined in
   [PCEP-GMPLS] as follows:

      o Extensions to the ERO, RRO, IRO, and XRO to carry label sub-
   objects for SDH/SONET, OTN, and DWDM networks.

      o Extended objects to support the inclusion of the label and
   unnumbered links.

      o END-POINTS (Generalized END-POINTS Object Type)

      o BANDWIDTH (Generalized BANDWIDTH Object Type)


      o IF_ID_ERROR_SPEC (extending [Stateful-PCE] section 7.3.4 that
   only considers the use of RSVP ERROR_SPEC)

   The END-POINTS object SHOULD be carried within the attribute-list to
   specify the endpoints pertaining to the reported LSP. The XRO object
   MAY be carried to specify the network resources that the reported
   LSP avoids and a PCE SHOULD consider avoid these network resources
   during the process of re-optimizing after this LSP is delegated to

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   the PCE.  To be more specific, the <attribute-list> is updated as

   <attribute-list> ::= [<END-POINTS>]

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

   If the LSP being reported protects another LSP, the PROTECTION-
   ATTRIBUTE TLV [PCEP-GMPLS] MUST be included in the LSPA object to
   describe its attributes and restrictions.  Moreover, if the status
   of the protecting LSP changes from non-operational to operational,
   this SHOULD to be synchronized to the stateful PCE using a PCRpt

2.4.  Modification of Existing PCEP Messages and Procedures

   One of the advantages mentioned in [RFC8051] is that the stateful
   nature of a PCE simplifies the information conveyed in PCEP messages,
   notably between PCC and PCE, since it is possible to refer to PCE
   managed state for active LSPs. To be more specific, with a stateful
   PCE, it is possible to refer to an LSP with a unique identifier in
   the scope of the PCC-PCE session and thus use such identifier to
   refer to that LSP. Note this MAY also be applicable to packet

2.4.1. Modification for LSP Re-optimization

   The Request Parameters (RP) object on a Path Computation Request
   (PCReq) message carries the R bit.  When set, this indicates that
   the PCC is requesting re-optimization of an existing LSP. Upon
   receiving such a PCReq, a stateful PCE SHOULD perform the    re-
   optimization in the following cases:

      - The existing bandwidth and route information of the LSP to be
   re-optimized is provided in the PCReq message using the BANDWIDTH
   object and the ERO.

      - The existing bandwidth and route information is not supplied in
   the PCReq message, but can be found in the PCE's LSP-DB.  In this
   case, the LSP MUST be identified using an LSP identifier carried in

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   the PCReq message, and that fact requires that the LSP identifier
   was previously supplied either by the PCC in a PCRpt message or by
   the PCE in a PCRep.  [Stateful-PCE] defines how this is achieved
   using a combination of the per-node LSP identifier (PLSP-ID) and the
   PCC's address.

   If no LSP state information is available to carry out    re-
   optimization, the stateful PCE should report the error "LSP state
   information unavailable for the LSP re-optimization" (Error Type =
   TBD1, Error value= TBD2).

2.4.2. Modification for Route Exclusion

   [RFC5521] defines a mechanism for a PCC to request or demand that
   specific nodes, links, or other network resources are excluded from
   paths computed by a PCE.  A PCC may wish to request the computation
   of a path that avoids all link and nodes traversed by some other LSP.

      To this end this document defines a new sub-object for use with
   route exclusion defined in [RFC5521].  The LSP exclusion sub-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
     |X|Type (TBD3) |     Length    |   Attributes  |    Flag        |
    |               PLSP-ID                   |      Reserved       |

      X bit and Attribute fields are defined in [RFC5521].
      X bit:  indicates whether the exclusion is mandatory (X=1) and
   MUST be accommodated, or desired (X=0) and SHOULD be accommodated.

      Type: Subobject Type for an LSP exclusion sub-object. Value of
   TBD3. To be assigned by IANA.

     Length: The Length contains the total length of the subobject in
   bytes, including the Type and Length fields.

      Attributes: indicates how the exclusion object is to be
   interpreted. Currently, Interface (Attributes = 0), Node (Attributes
   =1) and SRLG (Attributes =2) are defined in [RFC5521] and this
   document does not define new values.

      Flags: This field may be used to further specify the exclusion
   constraint with regard to the LSP. Currently, no values are defined.

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     PLSP-ID: This is the identifier given to a LSP and is unique in
   the context of the PCC address as defined in [Stateful-PCE].

     Reserved: MUST be transmitted as zero and SHOULD be ignored on

   This sub-object is OPTIONAL in the exclude route object (XRO) and
   can be present multiple times.  When a stateful PCE receives a PCReq
   message carrying this sub-object, it SHOULD search for the
   identified LSP in its LSP-DB and then exclude it from the new path
   computation all resources used by the identified LSP.  If the
   stateful PCE cannot recognize one or more of the received LSP
   identifiers, it should send an error message PCErr reporting "The
   LSP state information for route exclusion purpose cannot be found"
   (Error-type = TBD1, Error-value = TBD4).  Optionally, it may provide
   with the unrecognized identifier information to the requesting PCC
   using the error reporting techniques described in [RFC5440].

2.5. Object Encoding

   Note that, as is stated in Section 7 of [Stateful-PCE], the P flag
   and the I flag of the PCEP objects used on PCUpd and PCRpt messages
   SHOULD be set to 0 on transmission and SHOULD be ignored on receipt
   since these flags are exclusively related to path computation

3. IANA Considerations

   IANA is requested to allocate new Types for the TLV/Object defined
   in this document.

3.1. New PCEP Error Codes

   IANA is requested to make the following allocation in the "PCEP-
   ERROR Object Error Types and Values" registry.

   Error Type        Meaning                                Reference

   TBD1         LSP state information missing              [This.I-D]

   Error-value TBD2:    LSP state information unavailable  [This.I-D]

                    for the LSP re-optimization

   Error-value TBD4:   LSP state information for route

                   exclusion purpose cannot be found       [This.I-D]

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3.2. New Subobject for the Exclude Route Object

   IANA maintains the "PCEP Parameters" registry containing a
   subregistry called "PCEP Objects".  This registry has a subregistry
   for the XRO (Exclude Route Object) listing the sub-objects that can
   be carried in the XRO.  IANA is requested to assign a further sub-
   object that can be carried in the XRO as follows:

      Value       Description                    Reference


      TBD3        LSP identifier sub-object     [This.I-D]

4. Manageability Considerations

   The description and functionality specifications presented related
   to stateful PCEs should also comply with the manageability
   specifications covered in Section 8 of [RFC4655]. Furthermore, a
   further list of manageability issues presented in [Stateful-PCE]
   should also be considered.

   Additional considerations are presented in the next sections.

4.1. Requirements on Other Protocols and Functional Components

   When the detailed route information is included for LSP state
   synchronization (either at the initial stage or during LSP state
   report process), this requires the ingress node of an LSP carry the
   RRO object in order to enable the collection of such information.

5. Security Considerations

   This draft provides additional extensions to PCEP so as to
   facilitate stateful PCE usage in GMPLS-controlled networks, on top
   of [Stateful-PCE].  The PCEP extensions to support GMPLS-controlled
   networks should be considered under the same security as for MPLS
   networks, as noted in [RFC7025]. Therefore, the security
   considerations elaborated in [RFC5440] still apply to this draft.
   Furthermore, [Stateful-PCE] provides a detailed analysis of the
   additional security issues incurred due to the new extensions and
   possible solutions needed to support for the new stateful PCE
   capabilities and they apply to this document as well.

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6. Acknowledgement

   We would like to thank Adrian Farrel and Cyril Margaria for the
   useful comments and discussions.

7. References

7.1. Normative References

   [RFC2119] Bradner, S., "Key words for use in RFCs to indicate
             requirements levels", RFC 2119, March 1997.

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

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

   [Stateful-PCE] Crabbe, E., Medved, J., Varga, R., Minei, I., "PCEP
             Extensions for Stateful PCE", draft-ietf-pce-stateful-pce,
             work in progress.

   [PCEP-GMPLS] Margaria, C., Gonzalez de Dios, O., Zhang, F., "PCEP
             extensions for GMPLS", draft-ietf-pce-gmpls-pcep-
             extensions, work in progress.

7.2. Informative References

   [RFC8051] Zhang, X., Minei, I., et al, "Applicability of Stateful
             Path Computation Element (PCE) ", RFC 8051, January 2017.

   [Sync-OPT] Crabbe, E., Minei, I., Medved, J., Varga, R., Zhang, X.,
             and D. Dhody, "Optimizations of Label Switched Path State
             Synchronization Procedures for a Stateful PCE", draft-
             ietf-pce-stateful-sync-optimizations, work in progress.

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8. Contributors' Address

   Dhruv Dhody
   Huawei Technology
   Leela Palace
   Bangalore, Karnataka 560008

   EMail: dhruvd@huawei.com

   Yi Lin
   Huawei Technologies
   F3-5-B R&D Center, Huawei Base
   Bantian, Longgang District
   Shenzhen 518129 P.R.China

   Phone: +86-755-28972914
   Email: yi.lin@huawei.com

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Authors' Addresses

   Xian Zhang
   Huawei Technologies
   F3-5-B R&D Center, Huawei Base
   Bantian, Longgang District
   Shenzhen 518129 P.R.China

   Phone: +86-755-28972645
   Email: zhang.xian@huawei.com

   Young Lee
   5340 Legacy Drive, Suite 170
   Plano, TX  75023

   Phone: +1 469 278 5838
   EMail: ylee@huawei.com

   Fatai Zhang
   F3-5-B R&D Center, Huawei Base
   Bantian, Longgang District
   P.R. China

   Phone: +86-755-28972912
   Email: zhangfatai@huawei.com

   Ramon Casellas
   Av. Carl Friedrich Gauss n7
   Castelldefels, Barcelona 08860

   Email: ramon.casellas@cttc.es

   Oscar Gonzalez de Dios
   Telefonica Investigacion y Desarrollo
   Emilio Vargas 6
   Madrid,   28045

   Phone: +34 913374013

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   Email: ogondio@tid.es

   Zafar Ali
   Cisco Systems
   Email: zali@cisco.com

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