PCEP Extensions for Receiving SRLG Information
draft-dhody-pce-recv-srlg-02

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Replaces draft-dhody-pce-srlg-collection
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PCE Working Group                                               D. Dhody
Internet-Draft                                                  F. Zhang
Intended status: Standards Track                                X. Zhang
Expires: February 12, 2015                           Huawei Technologies
                                                                V. Lopez
                                                     O. Gonzalez de Dios
                                                          Telefonica I+D
                                                         August 11, 2014

             PCEP Extensions for Receiving SRLG Information
                      draft-dhody-pce-recv-srlg-02

Abstract

   The Path Computation Element (PCE) provides functions of path
   computation in support of traffic engineering (TE) in networks
   controlled by Multi-Protocol Label Switching (MPLS) and Generalized
   MPLS (GMPLS).

   This document provides extensions for the Path Computation Element
   Protocol (PCEP) to receive Shared Risk Link Group (SRLG) information
   during path computation via encoding this information in the path
   computation reply message.

Status of This Memo

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

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   This Internet-Draft will expire on February 12, 2015.

Copyright Notice

   Copyright (c) 2014 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   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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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Usage of SRLG . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  PCEP Requirements . . . . . . . . . . . . . . . . . . . . . .   4
   5.  Extension to PCEP . . . . . . . . . . . . . . . . . . . . . .   4
     5.1.  The Extension of the RP Object  . . . . . . . . . . . . .   5
     5.2.  SRLG Subobject in ERO . . . . . . . . . . . . . . . . . .   5
   6.  Other Considerations  . . . . . . . . . . . . . . . . . . . .   6
     6.1.  Backward Compatibility  . . . . . . . . . . . . . . . . .   6
     6.2.  Confidentiality via PathKey . . . . . . . . . . . . . . .   6
     6.3.  Coherent SRLG IDs . . . . . . . . . . . . . . . . . . . .   6
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   8.  Manageability Considerations  . . . . . . . . . . . . . . . .   7
     8.1.  Control of Function and Policy  . . . . . . . . . . . . .   7
     8.2.  Information and Data Models . . . . . . . . . . . . . . .   7
     8.3.  Liveness Detection and Monitoring . . . . . . . . . . . .   7
     8.4.  Verify Correct Operations . . . . . . . . . . . . . . . .   7
     8.5.  Requirements On Other Protocols . . . . . . . . . . . . .   7
     8.6.  Impact On Network Operations  . . . . . . . . . . . . . .   7
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
     9.1.  New Subobjects for the ERO Object . . . . . . . . . . . .   8
   10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   8
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     11.1.  Normative References . . . . . . . . . . . . . . . . . .   8
     11.2.  Informative References . . . . . . . . . . . . . . . . .   8
   Appendix A.  Contributor Addresses  . . . . . . . . . . . . . . .  10

1.  Introduction

   As per [RFC4655], PCE based path computation model is deployed in
   large, multi-domain, multi-region, or multi-layer networks.  In such
   case PCEs may cooperate with each other to provide end to end optimal
   path.

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   It is important to understand which TE links in the network might be
   at risk from the same failures.  In this sense, a set of links may
   constitute a 'shared risk link group' (SRLG) if they share a resource
   whose failure may affect all links in the set [RFC4202].  H-LSP
   (Hierarchical LSP) or S-LSP (Stitched LSP) can be used for carrying
   one or more other LSPs as described in [RFC4206] and [RFC6107].
   H-LSP and S-LSP may be computed by PCE(s) and further form as a TE
   link.  The SRLG information of such LSPs can be obtained during path
   computation itself and encoded in the PCEP Path Computation Reply
   (PCRep) message.  [I-D.zhang-ccamp-gmpls-uni-app] describes the use
   of a PCE for end to end User-Network Interface (UNI) path
   computation.

   Note that [I-D.ietf-ccamp-rsvp-te-srlg-collect] specifies a extension
   to Resource ReserVation Protocol-Traffic Engineering (RSVP-TE) where
   SRLG information is collected at the time of signaling.  But in case
   a PCE or cooperating PCEs are used for path computation it is
   recommended that SRLG information is provided by the PCE(s) during
   the path computation itself.

   [I-D.farrel-interconnected-te-info-exchange] describes a scaling
   problem with SRLGs in multi-layer environment and introduce a concept
   of Macro SRLG (MSRLG).  Lower layer SRLG are abstracted at the time
   of path computation and can be the basis to generate such a Macro
   SRLG at the PCE.

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 [RFC2119].

2.  Terminology

   The following terminology is used in this document.

   CPS:  Confidential Path Segment.  A segment of a path that contains
      nodes and links that the policy requires not to be disclosed
      outside the domain.

   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.

   SRLG:  Shared Risk Link Group.

   UNI:  User-Network Interface.

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3.  Usage of SRLG

   [RFC4202] states that a set of links may constitute a 'shared risk
   link group' (SRLG) if they share a resource whose failure may affect
   all links in the set.  For example, two fibers in the same conduit
   would be in the same SRLG.  If an LSR is required to have multiple
   diversely routed LSPs to another LSR, the path computation should
   attempt to route the paths so that they do not have any links in
   common, and such that the path SRLGs are disjoint.

   In case a PCE or cooperating PCEs are used for path computation, the
   SRLG information is provided by the PCE(s).  For example, disjoint
   paths for inter-domain or inter-layer LSPs.  In order to achieve path
   computation for a secondary (backup) path, a PCC may request the PCE
   for a route that must be SRLG disjoint from the primary (working)
   path.  The Exclude Route Object (XRO) [RFC5521] is used to specify
   SRLG information to be explicitly excluded.

4.  PCEP Requirements

   Following key requirements are identified for PCEP to receive SRLG
   information during path computation:

   SRLG Indication:  The PCEP speaker must be capable of indicating
      whether the SRLG information of the path should be received during
      the path computation procedure.

   SRLG:  If requested, the SRLG information should be received during
      the path computation and encoded in the PCRep message.

   Cooperating PCEs [RFC4655] with inter-PCE Communication work together
   to provide the end to end optimal path as well as the SRLG
   information of this path.  During inter-domain or inter-layer path
   computation, the aggregating PCE (Parent PCE [RFC6805] or Ingress
   PCE(1) [RFC5441] or Higher-Layer PCE [RFC5623]) should receive the
   SRLG information of path segments from other PCEs and provide the end
   to end SRLG information of the optimal path to the Path Computation
   Client (PCC).

5.  Extension to PCEP

   This document extends the existing RP (Request Parameters) object
   [RFC5440] so that a PCEP speaker can request SRLG information during
   path computation.  The SRLG subobject maybe carried inside the
   Explicit Route Object (ERO) in the PCRep message.

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5.1.  The Extension of the RP Object

   This document adds the following flags to the RP Object:

   S (SRLG - 1 bit):  when set, in a PCReq message, this indicates that
      the SRLG information of the path should be provided in the PCRep
      message.  Otherwise, when cleared, this indicates that the SRLG
      information should not be included in the PCRep message.  In a
      PCRep message, when the S bit is set this indicates that the
      returned path in ERO also carry the SRLG information; otherwise
      (when the S bit is cleared), the returned path does not carry SRLG
      information.

5.2.  SRLG Subobject in ERO

   As per [RFC5440], ERO is used to encode the path and is carried
   within a PCRep message to provide the computed path when computation
   was successful.

   The SRLG of a path is the union of the SRLGs of the links in the path
   [RFC4202].  The SRLG subobject is defined in
   [I-D.ietf-ccamp-rsvp-te-srlg-collect] for ROUTE_RECORD object (RRO).
   The same subobject format (as shown below) can be encoded inside the
   ERO object in the PCRep message.

      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |      Type     |     Length    |            Reserved           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                 SRLG ID 1 (4 bytes)                           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     ~                           ......                              ~
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                 SRLG ID n (4 bytes)                           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The meaning and description of Type, Length and SRLG ID can be found
   in [I-D.ietf-ccamp-rsvp-te-srlg-collect].  Reserved field SHOULD be
   set to zero on transmission and MUST be ignored on receipt.

   The SRLG subobject should be encoded inside the ERO object in the
   PCRep message when the S-Bit (SRLG) is set in the PCReq message.

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6.  Other Considerations

6.1.  Backward Compatibility

   If a PCE receives a request and the PCE does not understand the new
   SRLG flag in the RP object, then the PCE SHOULD reject the request.

   If PCEP speaker receives a PCRep message with SRLG subobject that it
   does not support or recognize, it must act according to the existing
   processing rules of ERO.

6.2.  Confidentiality via PathKey

   [RFC5520] defines a mechanism to hide the contents of a segment of a
   path, called the Confidential Path Segment (CPS).  The CPS may be
   replaced by a path-key that can be conveyed in the PCEP and signaled
   within in a RSVP-TE ERO.

   When path-key confidentiality is used, encoding SRLG information in
   PCRep along with the path-key could be useful to compute a SRLG
   disjoint backup path at the later instance.

   The path segment that needs to be hidden (that is, CPS) MAY be
   replaced in the ERO with a PKS.  The PCE MAY use the SRLG Sub-objects
   in the ERO along with the PKS sub-object.

6.3.  Coherent SRLG IDs

   In a multi-layer multi-domain scenario, SRLG ids may be configured by
   different management entities in each layer/domain.  In such
   scenarios, maintaining a coherent set of SRLG IDs is a key
   requirement in order to be able to use the SRLG information properly.
   Thus, SRLG IDs must be unique.  Note that current procedure is
   targeted towards a scenario where the different layers and domains
   belong to the same operator, or to several coordinated administrative
   groups.  Ensuring the aforementioned coherence of SRLG IDs is beyond
   the scope of this document.  Further scenarios, where coherence in
   the SRLG IDs cannot be guaranteed are out of the scope of the present
   document and are left for further study.

7.  Security Considerations

   This document does not add any new security concerns beyond those
   discussed in [RFC5440].

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8.  Manageability Considerations

8.1.  Control of Function and Policy

   A PCE involved in inter-domain or inter-layer path computation should
   be capable of being configured with a SRLG processing policy to
   specify if the SRLG IDs of the domain or specific layer network can
   be exposed to the PCC outside the domain or layer network, or whether
   they should be summarized, mapped to values that are comprehensible
   to PCC outside the domain or layer network, or removed entirely.

8.2.  Information and Data Models

   [I-D.ietf-pce-pcep-mib] describes the PCEP MIB, there are no new MIB
   Objects for this document.

8.3.  Liveness Detection and Monitoring

   Mechanisms defined in this document do not imply any new liveness
   detection and monitoring requirements in addition to those already
   listed in [RFC5440].

8.4.  Verify Correct Operations

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

8.5.  Requirements On Other Protocols

   Mechanisms defined in this document do not imply any new requirements
   on other protocols.

8.6.  Impact On Network Operations

   Mechanisms defined in this document do not have any impact on network
   operations in addition to those already listed in [RFC5440].

9.  IANA Considerations

   IANA assigns values to PCEP parameters in registries defined in
   [RFC5440].  IANA is requested to make the following additional
   assignments.

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9.1.  New Subobjects for the ERO Object

   IANA has previously assigned an Object-Class and Object-Type to the
   ERO carried in PCEP messages [RFC5440].  IANA also maintains a list
   of subobject types valid for inclusion in the ERO.

   IANA is requested to assign one new subobject types for inclusion in
   the ERO as follows:

              Subobject        Meaning                Reference
               xx (TBA)        SRLG sub-object        This document

10.  Acknowledgments

   Special thanks to the authors of
   [I-D.ietf-ccamp-rsvp-te-srlg-collect].  This document borrows some of
   text from it.

11.  References

11.1.  Normative References

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

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

11.2.  Informative References

   [RFC4202]  Kompella, K. and Y. Rekhter, "Routing Extensions in
              Support of Generalized Multi-Protocol Label Switching
              (GMPLS)", RFC 4202, October 2005.

   [RFC4206]  Kompella, K. and Y. Rekhter, "Label Switched Paths (LSP)
              Hierarchy with Generalized Multi-Protocol Label Switching
              (GMPLS) Traffic Engineering (TE)", RFC 4206, October 2005.

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

   [RFC5441]  Vasseur, JP., 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.

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   [RFC5520]  Bradford, R., Vasseur, JP., and A. Farrel, "Preserving
              Topology Confidentiality in Inter-Domain Path Computation
              Using a Path-Key-Based Mechanism", RFC 5520, 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.

   [RFC5623]  Oki, E., Takeda, T., Le Roux, JL., and A. Farrel,
              "Framework for PCE-Based Inter-Layer MPLS and GMPLS
              Traffic Engineering", RFC 5623, September 2009.

   [RFC6107]  Shiomoto, K. and A. Farrel, "Procedures for Dynamically
              Signaled Hierarchical Label Switched Paths", RFC 6107,
              February 2011.

   [RFC6805]  King, D. and A. Farrel, "The Application of the Path
              Computation Element Architecture to the Determination of a
              Sequence of Domains in MPLS and GMPLS", RFC 6805, November
              2012.

   [I-D.ietf-ccamp-rsvp-te-srlg-collect]
              Zhang, F., Dios, O., Li, D., Margaria, C., Hartley, M.,
              and Z. Ali, "RSVP-TE Extensions for Collecting SRLG
              Information", draft-ietf-ccamp-rsvp-te-srlg-collect-06
              (work in progress), July 2014.

   [I-D.ietf-pce-pcep-mib]
              Koushik, K., Emile, S., Zhao, Q., King, D., and J.
              Hardwick, "Path Computation Element Protocol (PCEP)
              Management Information Base", draft-ietf-pce-pcep-mib-09
              (work in progress), July 2014.

   [I-D.farrel-interconnected-te-info-exchange]
              Farrel, A., Drake, J., Bitar, N., Swallow, G., Ceccarelli,
              D., and X. Zhang, "Problem Statement and Architecture for
              Information Exchange Between Interconnected Traffic
              Engineered Networks", draft-farrel-interconnected-te-info-
              exchange-06 (work in progress), July 2014.

   [I-D.zhang-ccamp-gmpls-uni-app]
              Zhang, F., Dios, O., Farrel, A., Zhang, X., and D.
              Ceccarelli, "Applicability of Generalized Multiprotocol
              Label Switching (GMPLS) User-Network Interface (UNI)",
              draft-zhang-ccamp-gmpls-uni-app-05 (work in progress),
              February 2014.

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Appendix A.  Contributor Addresses

   Udayasree Palle
   Huawei Technologies
   Leela Palace
   Bangalore, Karnataka  560008
   India

   EMail: udayasree.palle@huawei.com

   Avantika
   Huawei Technologies
   Leela Palace
   Bangalore, Karnataka  560008
   India

   EMail: avantika.sushilkumar@huawei.com

Authors' Addresses

   Dhruv Dhody
   Huawei Technologies
   Leela Palace
   Bangalore, Karnataka  560008
   India

   EMail: dhruv.ietf@gmail.com

   Fatai Zhang
   Huawei Technologies
   Bantian, Longgang District
   Shenzhen, Guangdong  518129
   P.R.China

   EMail: zhangfatai@huawei.com

   Xian Zhang
   Huawei Technologies
   Bantian, Longgang District
   Shenzhen, Guangdong  518129
   P.R.China

   EMail: zhang.xian@huawei.com

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   Victor Lopez
   Telefonica I+D
   Distrito Telefonica
   Edificio Sur 3, 3rd floor
   Madrid  28050
   Spain

   EMail: victor.lopezalvarez@telefonica.com

   Oscar Gonzalez de Dios
   Telefonica I+D
   Distrito Telefonica
   Edificio Sur 3, 3rd floor
   Madrid    28050
   Spain

   EMail: oscar.gonzalezdedios@telefonica.com

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