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Versions: 00 01 draft-ietf-pce-association-diversity

PCE Working Group                                           S. Litkowski
Internet-Draft                                                    Orange
Intended status: Standards Track                            S. Sivabalan
Expires: May 27, 2017                                Cisco Systems, Inc.
                                                                C. Barth
                                                        Juniper Networks
                                                       November 23, 2016


Path Computation Element communication Protocol extension for signaling
                        LSP diversity constraint
              draft-litkowski-pce-association-diversity-01

Abstract

   This document introduces a simple mechanism to signal path diversity
   for a group of Label Switched Paths (LSPs) via an extension to the
   Path Computation Element Communication Protocol (PCEP).

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on May 27, 2017.

Copyright Notice

   Copyright (c) 2016 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



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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Motivation  . . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Protocol extension  . . . . . . . . . . . . . . . . . . . . .   6
     4.1.  Association group . . . . . . . . . . . . . . . . . . . .   6
     4.2.  Optional TLVs . . . . . . . . . . . . . . . . . . . . . .   6
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
     6.1.  Association object Type Indicators  . . . . . . . . . . .   8
   7.  Manageability Considerations  . . . . . . . . . . . . . . . .   9
     7.1.  Control of Function and Policy  . . . . . . . . . . . . .   9
     7.2.  Information and Data Models . . . . . . . . . . . . . . .   9
     7.3.  Liveness Detection and Monitoring . . . . . . . . . . . .   9
     7.4.  Verify Correct Operations . . . . . . . . . . . . . . . .   9
     7.5.  Requirements On Other Protocols . . . . . . . . . . . . .   9
     7.6.  Impact On Network Operations  . . . . . . . . . . . . . .   9
   8.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   9
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   9
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   [I-D.ietf-pce-association-group] introduces a generic mechanism to
   create a grouping of LSPs which can then be used to define
   associations between a set of LSPs and a set of attributes (such as
   configuration parameters or behaviours) and is equally applicable to
   the active and passive modes of a stateful PCE
   [I-D.ietf-pce-stateful-pce] or a stateless PCE [RFC5440].

   This document specifies a PCEP extension to signal that a particular
   group of LSPs should use diverse paths including the requested type
   of diversity.

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].





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2.  Terminology

   The following terminology is used in this document.

   LSR:  Label Switch Router.

   MPLS:  Multiprotocol Label Switching.

   PCC:  Path Computation Client.  Any client application requesting a
      path computation to be performed by a Path Computation Element.

   PCE:  Path Computation Element.  An entity (component, application,
      or network node) that is capable of computing a network path or
      route based on a network graph and applying computational
      constraints.

   PCEP:  Path Computation Element Communication Protocol.

   SRLG:  Shared Risk Link Group.

3.  Motivation

   Path diversity is a very common use case today in IP/MPLS networks
   especially for layer 2 transport over MPLS.  A customer may request
   that the operator provide two end-to-end disjoint paths across the
   IP/MPLS core.  The customer may use those paths as primary/backup or
   active/active.

   Different level of disjointness may be offered:

   o  Link disjointness: the paths of the associated LSPs should transit
      different links (but may use common nodes or different links that
      may have some shared fate).

   o  Node disjointness: the paths of the associated LSPs should transit
      different nodes (but may use different links that may have some
      shared fate).

   o  SRLG disjointness: the paths of the associated LSPs should transit
      different links that do not share fate (but may use common transit
      nodes).

   o  Node+SRLG disjointness: the paths of the associated LSPs should
      transit different links that do not have any common shared fate
      and should transit different nodes.

   The associated LSPs may originate from the same or from different
   head-end(s) and may terminate at the same or different tail-end(s).



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            _________________________________________
           /                                         \
          /        +------+                           \
         |         | PCE  |                            |
         |         +------+                            |
         |                                             |
         |          ***********************>           |
         | +------+           10             +------+  |
   CE1 ****| PE 1 | ----- R1 ---- R2 ------- | PE 2 |**** CE2
         | +------+       |        |         +------+  |
         |                |        |                   |
         |                |        |                   |
         | +------+       |        |         +------+  |
   CE3 ****| PE 3 | ----- R3 ---- R4 ------- | PE 4 |**** CE4
         | +------+ ***********************> +------+  |
         |                                             |
          \                                           /
           \_________________________________________/


            Figure 1 - Disjoint paths with different head-ends

   In the figure above, the customer wants to have two disjoint paths
   between CE1/CE2 and CE3/CE4.  From an IP/MPLS network point view, in
   this example, the CEs are connected to different PEs to maximize
   their disjointness.  When LSPs originate from different head-ends,
   distributed computation of diverse paths can be difficult.  Whereas,
   computation via a centralized PCE ensures path disjointness
   correctness and simplicity.

   Using PCEP, the PCC MUST indicate that disjoint path computation is
   required, such indication SHOULD include disjointness parameters such
   as the type of disjointness, the disjoint group-id, and any
   customization parameters according to local policy.

   The PCC can use the generic mechanism as per
   [I-D.ietf-pce-association-group] to associate a set of LSPs with a
   particular disjoint-group.

   The management of the disjoint group-ids will be a key point for the
   operator as the Association ID field is limited to 65535.  The local
   configuration of IPv4/IPv6 association source, or Global Association
   Source/Extended Association ID should allow to overcome this
   limitation.  For example, when a PCC or PCE initiates all the LSPs in
   a particular disjoint-group, it can set the IPv4/IPv6 association
   source can be set to one of its IP address.  When disjoint LSPs are
   initiated from different head-ends, a unique association identifier
   SHOULD be used for those LSPs: this can be achieved by setting the



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   IPv4/IPv6 source address to a common value (zero value can be used)
   as well as the Association ID.



          Initiate & Monitor LSP
                   |
                   |                          PCReq
                   V                  {Disjoint-group Y}
                +-----+                   ----------------> +-----+
     _ _ _ _ _ _| PCE |                  |                  | PCE |
    |           +-----+                  |      ----------> +-----+
    | PCEInitiate                        |     |    PCReq
    |{Disjoint-group X}                  |     | {Disjoint-group Y}
    |                                    |     |
    |              .-----.               |     |         .-----.
    |             (       )              |  +----+      (       )
    |         .--(         )--.          |  |PE 1|--.--(         )--.
    V        (                 )         |  +----+ (                 )
  +---+     (                   )        |        (                   )
  |PCC|----(   (G)MPLS network    )   +----+     ( (G)MPLS network     )
  +---+     (                   )     |PE 3|------(                   )
Disjoint-group X               )      +----+       (                 )
{Monitor LSP} '--(         )--'                     '--(         )--'
                  (       )                             (       )
                   '-----'                               '-----'

 Case 1: Disjointness initiated by    Case 2: Disjointness initiated by
         PCE and enforced by PCC             PCC and enforced by PCE


     Figure 2 - Sample use-cases for carrying disjoint-group over PCEP
                                  session

   Using the disjoint-group within a PCUpdate or PCInit may have two
   purposes:

   o  Information: in case the PCE is performing the path computation,
      it may communicate to the PCC the locally used configured
      parameters in the attribute-list of the LSP.

   o  Configuration: in case the PCC is performing the path computation
      but the PCE (without computation engine) is managing the LSP
      parameters, the PCE should add the disjoint-group within the
      PCUpdate message to communicate to the PCC the disjointness
      constraint.





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4.  Protocol extension

4.1.  Association group

   As per [I-D.ietf-pce-association-group], LSPs are associated with
   other LSPs with which they interact by adding them to a common
   association group.  The Association ID will be used to identify the
   disjoint group a set of LSPs belongs to.  This document defines four
   new Association types, based on the generic Association object -

   o  Association type = TBD1 ("Disjointness Association Type") for link
      disjoint group.

   o  Association type = TBD2 ("Disjointness Association Type") for node
      disjoint group.

   o  Association type = TBD3 ("Disjointness Association Type") for srlg
      disjoint group.

   o  Association type = TBD4 ("Disjointness Association Type") for
      node+srlg disjoint group.

   A disjoint group can have two or more LSPs.  But a PCE may be limited
   in how many LSPs it can take into account when computing
   disjointness: usually PCEs are able to compute a pair of disjoint
   paths.  If a PCE receives more LSPs in the group than it can handle
   in its computation algorithm, it SHOULD apply disjointness
   computation to only a subset of LSPs in the group.  The subset of
   disjoint LSPs will be decided by the implementation.

   Local polices on the PCC or PCE MAY define the computational behavior
   for the other LSPs in the group.  For example, the PCE may provide no
   path, a shortest path, or a constrained path based on relaxing
   disjointness, etc.

   Associating a particular LSP to multiple disjoint groups is
   authorized from a protocol perspective, however there is no insurance
   that the PCE will be able to compute properly the multi-disjointness
   constraint.

4.2.  Optional TLVs

   The disjoint group MAY carry some optional TLVs including but not
   limited to:

   o  VENDOR-INFORMATION-TLV: Used to communicate arbitrary vendor
      specific behavioral information, described in [RFC7150].




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   o  DISJOINTNESS-INFORMATION-TLV: Used to communicate some
      disjointness specific parameters.

   The DISJOINTNESS-INFORMATION-TLV is shown in the following figure:

        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 = [TBD5]         |            Length             |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |           Flags                                           |P|S|
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Flags:

      *  P: shortest path, this particular LSP in the group SHOULD use
         the shortest constrained path and others MAY use a non shortest
         constrained path.  The shortest constrained path is the
         shortest path (from the requested metric point of view) that
         fills all the LSP constraints without taking into account the
         disjointness constraint.  This means that an LSP with P flag
         set should be placed as if the disjointness constraint has not
         been configured, while the other LSP in the association with P
         flag unset should be placed by taking into account the
         disjointness constraint.  Setting P flag changes the
         relationship between LSPs to a unidirectional relationship (LSP
         1 with P=0 depends of LSP 2 with P=1, but LSP 2 with P=1 does
         not depend of LSP 1 with P=0).

      *  S: strict disjointness, when set if disjoint paths cannot be
         found, PCE should return no path for LSPs that could not be be
         disjoint.  When unset, PCE is allowed to relax disjointness by
         using either using a lower disjoint type (link instead of node)
         or relaxing disjointness constraint at all.

   If a PCEP speaker receives a disjoint-group without DISJOINTNESS-
   INFORMATION-TLV, it SHOULD use its locally configured parameters or
   use the following default parameters:

   o  Strict disjointness is assumed.

   o  LSP can use a non shortest-path.

   If a PCEP speaker receives two LSPs with the same disjoint-group but
   with a different S flag value, it SHOULD apply a strict disjointness
   path computation for this disjoint-group (it considers S flag set for
   all LSPs).




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5.  Security Considerations

   This document defines one new type for association, which do not add
   any new security concerns beyond those discussed in [RFC5440],
   [I-D.ietf-pce-stateful-pce] and [I-D.ietf-pce-association-group] in
   itself.

6.  IANA Considerations

6.1.  Association object Type Indicators

   This document defines the following new association type originally
   defined in [I-D.ietf-pce-association-group].

  Value                     Name                             Reference

  TBD1                      Link Disjoint-group
                            Association Type                 [This I.D.]
  TBD2                      Node Disjoint-group
                            Association Type                 [This I.D.]
  TBD3                      SRLG Disjoint-group
                            Association Type                 [This I.D.]
  TBD4                      Node+SRLG Disjoint-group
                            Association Type                 [This I.D.]

   This document defines the following new PCEP TLV:

   Value     Name                                   Reference

   TBD5      DISJOINTNESS-INFORMATION-TLV           [This I.D.]


   IANA is requested to manage the space of flags carried in the
   DISJOINTNESS-INFORMATION TLV defined in this document, numbering them
   from 0 as the least significant bit.

   New bit numbers may be allocated in future.

   IANA is requested to allocate the following bit numbers in the
   DISJOINTNESS-INFORMATION-TLV flag space:

   Bit Number     Name                                   Reference
       0          Strict disjointness                    [This I.D.]
       1          Shortest-path                          [This I.D.]







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7.  Manageability Considerations

7.1.  Control of Function and Policy

   An operator MUST be allowed to configure the disjointness
   associations and parameters at PCEP peers and associate it with the
   LSPs.

7.2.  Information and Data Models

   [RFC7420] describes the PCEP MIB, there are no new MIB Objects for
   this document.

7.3.  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].

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 new requirements
   on other protocols.

7.6.  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].

8.  Acknowledgments

   A special thanks to author of [I-D.ietf-pce-association-group], this
   document borrow some of the text from it.

9.  References

9.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.



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   [RFC4655]  Farrel, A., Vasseur, J., and J. Ash, "A Path Computation
              Element (PCE)-Based Architecture", RFC 4655,
              DOI 10.17487/RFC4655, August 2006,
              <http://www.rfc-editor.org/info/rfc4655>.

   [RFC5440]  Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
              Element (PCE) Communication Protocol (PCEP)", RFC 5440,
              DOI 10.17487/RFC5440, March 2009,
              <http://www.rfc-editor.org/info/rfc5440>.

   [I-D.ietf-pce-association-group]
              Minei, I., Crabbe, E., Sivabalan, S., Ananthakrishnan, H.,
              Zhang, X., and Y. Tanaka, "PCEP Extensions for
              Establishing Relationships Between Sets of LSPs", draft-
              ietf-pce-association-group-01 (work in progress), July
              2016.

   [I-D.ietf-pce-stateful-pce]
              Crabbe, E., Minei, I., Medved, J., and R. Varga, "PCEP
              Extensions for Stateful PCE", draft-ietf-pce-stateful-
              pce-17 (work in progress), November 2016.

9.2.  Informative References

   [RFC7150]  Zhang, F. and A. Farrel, "Conveying Vendor-Specific
              Constraints in the Path Computation Element Communication
              Protocol", RFC 7150, DOI 10.17487/RFC7150, March 2014,
              <http://www.rfc-editor.org/info/rfc7150>.

   [RFC7420]  Koushik, A., Stephan, E., Zhao, Q., King, D., and J.
              Hardwick, "Path Computation Element Communication Protocol
              (PCEP) Management Information Base (MIB) Module",
              RFC 7420, DOI 10.17487/RFC7420, December 2014,
              <http://www.rfc-editor.org/info/rfc7420>.

   [I-D.ietf-pce-pce-initiated-lsp]
              Crabbe, E., Minei, I., Sivabalan, S., and R. Varga, "PCEP
              Extensions for PCE-initiated LSP Setup in a Stateful PCE
              Model", draft-ietf-pce-pce-initiated-lsp-07 (work in
              progress), July 2016.

Authors' Addresses

   Stephane Litkowski
   Orange

   EMail: stephane.litkowski@orange.com




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   Siva Sivabalan
   Cisco Systems, Inc.
   2000 Innovation Drive
   Kanata, Ontario  K2K 3E8
   Canada

   EMail: msiva@cisco.com


   Colby Barth
   Juniper Networks

   EMail: cbarth@juniper.net






































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