Path Computation Element (PCE) Protocol Extensions for Stateful PCE Usage in GMPLS-controlled Networks
draft-ietf-pce-pcep-stateful-pce-gmpls-07

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   o  Active LSP update is covered in Section 6.2 of [RFC8231]. Section
      4.1. of this document provides extension for its application in
      GMPLS-controlled networks.

  o  LSP state synchronization and LSP state report. This is a generic
     requirement already covered in Section 5.6. of [RFC8231].  However,
     there are further extensions required specifically for GMPLS-
     controlled networks and discussed in Section 4.2.

4. PCEP Extensions

4.1. LSP Update in GMPLS-controlled Networks

   [RFC8231] 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 parameters.

   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. There are other
   technology-specific attributes that need to be conveyed in the
   <intended-attribute-list> of the <path> object of the PCUpd message.
   Note that these path details in the PCUpd message are the same as
   the <attribute-list> of the PCRep message. See Section 4.2 for the
   details.

   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.

4.2. 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
   [RFC8231], 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 [RFC8232].

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   [RFC8231] 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 [RFC8231],
   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  IRO/XRO Extensions to support the inclusion/exclusion of labels
        and label sub-objects for GMPLS. (See Section 2.6 and 2.7 in
        [PCEP-GMPLS])

     o  END-POINTS (Generalized END-POINTS Object Type. See Section 2.5
        in [PCEP-GMPLS])

     o  BANDWIDTH (Generalized BANDWIDTH Object Type. See Section 2.3
        in [PCEP-GMPLS])

      o LSPA (PROTECTION ATTRIBUTE TLV, See Section 2.8 in [PCEP-GMPLS].

      o IF_ID_ERROR_SPEC (extending [RFC8231] 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
   the PCE.  To be more specific, the <attribute-list> is updated as
   follows:

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

   <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

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   of the protecting LSP changes from non-operational to operational,
   this SHOULD to be synchronized to the stateful PCE using a PCRpt
   message.

4.3.  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
   networks.

4.3.1. 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:

     o  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.

     o  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 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
         message.  [RFC8231] 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).

4.3.2. 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

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   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.

     PLSP-ID: This is the identifier given to a LSP and is unique in
     the context of the PCC address as defined in [RFC8231].

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

   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

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   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].

4.4. Object Encoding

   Note that, as is stated in Section 7 of [RFC8231], 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
   requests.

5. IANA Considerations

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

5.1. 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]

5.2. 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

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   ----------+------------------------------+-------------

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

6. 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 [RFC8231] should
   also be considered.

   Additional considerations are presented in the next sections.

6.1. 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.

7. Security Considerations

   This draft provides additional extensions to PCEP so as to
   facilitate stateful PCE usage in GMPLS-controlled networks, on top
   of [RFC8231].  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, [RFC8231] 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.

8. Acknowledgement

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

9. References

9.1. Normative References

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

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   [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.

   [RFC8231] Crabbe, E., Medved, J., Varga, R., Minei, I., "Path
             Computation Element Communication Protocol (PCEP)
             Extensions for Stateful PCE", RFC 8231, September 2017.

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

9.2. Informative References

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

   [RFC8232] 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", RFC 8232,
             September 2017.

10. Contributors' Address

   Dhruv Dhody
   Huawei Technology
   Leela Palace
   Bangalore, Karnataka 560008
   INDIA

   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 (Editor)
   Huawei
   5340 Legacy Drive, Suite 170
   Plano, TX  75023
   US

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

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

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

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

   Phone:
   Email: ramon.casellas@cttc.es

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

   Phone: +34 913374013

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   Email: ogondio@tid.es

   Zafar Ali
   Cisco Systems
   Email: zali@cisco.com

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