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Versions: 00 01 02 03 04 05 06 07 draft-ietf-pce-association-diversity

PCE Working Group                                               D. Dhody
Internet-Draft                                                     Q. Wu
Intended status: Standards Track                     Huawei Technologies
Expires: November 18, 2017                                  May 17, 2017


                  PCE support for Maximizing Diversity
                     draft-dhody-pce-of-diverse-07

Abstract

   The computation of one or a set of Traffic Engineering Label Switched
   Paths (TE LSPs) in MultiProtocol Label Switching (MPLS) and
   Generalized MPLS (GMPLS) networks is subject to a set of one or more
   specific optimization criteria, referred to as objective functions.

   In the Path Computation Element (PCE) architecture, a Path
   Computation Client (PCC) may want a set of services that are required
   to be diverse (disjointed) from each other.  In case when full
   diversity could not be achieved, it is helpful to maximize diversity
   as much as possible (or in other words, minimize the common shared
   resources).

   This document defines objective function code types for three new
   objective functions for this purpose to be applied to a set of
   synchronized path computation requests.

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
   Task Force (IETF).  Note that other groups may also distribute
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   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on November 18, 2017.








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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
   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
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   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  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Extension to PCEP . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Other Considerations  . . . . . . . . . . . . . . . . . . . .   4
     4.1.  Relationship between SVEC Diversity Flags and OF  . . . .   4
     4.2.  Inter-Domain Considerations . . . . . . . . . . . . . . .   5
     4.3.  Domain Diversity  . . . . . . . . . . . . . . . . . . . .   5
     4.4.  Diversity v/s Optimality  . . . . . . . . . . . . . . . .   5
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   6.  Manageability Considerations  . . . . . . . . . . . . . . . .   6
     6.1.  Control of Function and Policy  . . . . . . . . . . . . .   6
     6.2.  Information and Data Models . . . . . . . . . . . . . . .   6
     6.3.  Liveness Detection and Monitoring . . . . . . . . . . . .   6
     6.4.  Verify Correct Operations . . . . . . . . . . . . . . . .   6
     6.5.  Requirements On Other Protocols . . . . . . . . . . . . .   6
     6.6.  Impact On Network Operations  . . . . . . . . . . . . . .   7
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   8.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   7
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   7
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   7
   Appendix A.  Contributor Addresses  . . . . . . . . . . . . . . .   9
   Appendix B.  Example  . . . . . . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   [RFC5440] describes the specifications for the Path Computation
   Element Communication Protocol (PCEP).  PCEP specifies the
   communication between a Path Computation Client (PCC) and a Path



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   Computation Element (PCE), or between two PCEs based on the PCE
   architecture [RFC4655].

   Further [RFC5440] describes dependent path computation requests in
   which case computations cannot be performed independently of each
   other, and usually used for diverse path computation.  [RFC5440] and
   [RFC6006] describe the use of Synchronization VECtor (SVEC)
   dependency flags (i.e., Node, Link, or Shared Risk Link Group (SRLG)
   diverse flags).

   In some scenario it may be noted that full diversity cannot be
   achieved because of topology considerations, deployment
   considerations, transient network issues etc.  In this case it would
   be helpful to maximize diversity as much as possible (or in other
   words minimize the common shared resources (Node, Link or SRLG)
   between a set of paths during path computation).

   It is interesting to note that for non synchronized diverse path
   computation the X bit in Exclude Route Object (XRO) or Explicit
   Exclusion Route subobject (EXRS) [RFC5521] can be used, where X bit
   set as 1 indicates that the resource specified SHOULD be excluded
   from the path computed by the PCE, but MAY be included subject to PCE
   policy and the absence of a viable path that meets the other
   constraints and excludes the resource.  Thus X bit can be used in a
   way to maximize diversity (or minimize common shared resources) when
   full diversity cannot be achieved.

   This document defines objective function code types for three new
   objective functions for this purpose to be applied to a set of
   synchronized path computation requests.

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 terminology is as per [RFC5440].

3.  Extension to PCEP

   [RFC5541] describes and define Objective function (OF) used in PCEP
   protocol.






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   To minimize the common shared resources (Node, Link or SRLG) between
   a set of paths during path computation three new OF codes are
   proposed:

   MSL

   *  Name:  Minimize the number of shared (common) Links.

   *  Objective Function Code:  TBD1

   *  Description:  Find a set of paths such that it passes through the
      least number of shared (common) links.

   MSN

   *  Name:  Minimize the number of shared (common) Nodes.

   *  Objective Function Code:  TBD2

   *  Description:  Find a set of paths such that it passes through the
      least number of shared (common) nodes.

   MSS

   *  Name:  Minimize the number of shared (common) SRLG.

   *  Objective Function Code:  TBD3

   *  Description:  Find a set of paths such that it share least number
      of common SRLGs.

4.  Other Considerations

4.1.  Relationship between SVEC Diversity Flags and OF

   [RFC5440] uses SVEC diversity flag for node, link or SRLG to describe
   the potential disjointness between the set of path computation
   requests used in PCEP protocol.  [I-D.dwpz-pce-domain-diverse]
   further extends by adding domain-diverse O-bit in SVEC object and a
   new OF Code for minimizing the number of shared transit domain.

   This document defines three new OF codes to maximize diversity as
   much as possible, in other words, minimize the common shared
   resources (Node,Link or SRLG) between a set of paths.

   It may be interesting to note that the diversity flags in the SVEC
   object and OF for diversity can be used together.  Some example of
   usage are listed below -



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   o  SVEC object with node-diverse bit=1 - ensure full node-diversity.

   o  SVEC object with node-diverse bit=1 and OF=MSS - full node diverse
      with as much as SRLG-diversity as possible.

   o  SVEC object with domain-diverse bit=1;link diverse bit=1 and
      OF=MSS - full domain and node diverse path with as much as SRLG-
      diversity as possible.

   o  SVEC object with node-diverse bit=1 and OF=MSN - ensure full node-
      diversity.

4.2.  Inter-Domain Considerations

   The mechanics for synchronous end to end path computations using
   Backward-Recursive PCE-Based Computation (BRPC) procedure [RFC5441]
   described in [RFC6006].

   In H-PCE [RFC6805] architecture, the parent PCE is used to compute a
   multi-domain path based on the domain connectivity information.  The
   parent PCE may be requested to provide a end to end path or only the
   sequence of domains.  Child PCE should be able to request
   synchronized diverse end to end paths from its parent PCE.

   The new objective function described in this document can be used to
   maximize diversity when full diverse paths cannot be found.

4.3.  Domain Diversity

   As per [I-D.dwpz-pce-domain-diverse].

4.4.  Diversity v/s Optimality

   In case of non-synchronized path computation, PCE may be requested to
   provide an optimal primary path first and then PCC requests for a
   backup path with exclusion.  Note that this approach does not
   guarantee diversity comparing to disjoint path computations for
   primary and backup path in a synchronized manner.

   A synchronized path computation with diversity flags and/or objective
   function is used to make sure that both the primary path and the
   backup path can be computed simultaneously with full diversity or
   optimized to be as diverse as possible.  In the latter case we may
   sacrifice optimal path for diversity, thus there is a trade-off
   between the two.

   An implementation may further choose to analyze the trade-off i.e. it
   may send multiple request to PCE asking to optimize based on



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   diversity as well as say, cost and make an intelligent choice between
   them.

5.  Security Considerations

   PCEP security mechanisms are described in [RFC5440] and are used to
   secure entire PCEP messages.  Nothing in this document changes the
   message flows or introduces any new messages, so the security
   mechanisms set out in [RFC5440] continue to be applicable.

   This document add new OF codes that may optionally be carried on PCEP
   messages with OF object [RFC5541] and will be automatically secured
   using the mechanisms described in [RFC5440].

   If a PCEP message is vulnerable to attack (for example, because the
   security mechanisms are not used), then the OF object could be used
   as part of an attack; however, it is likely that other objects will
   provide far more significant ways of attacking a PCE or PCC in this
   case.

6.  Manageability Considerations

6.1.  Control of Function and Policy

   In addition to [RFC5440], the PCC should construct the SVECs to
   identify and associate diverse SVEC relationships.  Considerations
   for use of objective functions are mentioned in [RFC5541].

6.2.  Information and Data Models

   The PCEP MIB Module defined in [RFC7420], there are no additional
   parameters identified in this document.

6.3.  Liveness Detection and Monitoring

   [RFC5440] provides a sufficient description for this document.  There
   are no additional considerations.

6.4.  Verify Correct Operations

   [RFC5440] provides a sufficient description for this document.  There
   are no additional considerations.

6.5.  Requirements On Other Protocols

   [RFC5440] provides a sufficient description for this document.  There
   are no additional considerations.




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6.6.  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] and
   [RFC5541].

7.  IANA Considerations

   As described in Section 3, three new Objective Functions have been
   defined.  IANA has made the following allocations from the PCEP
   "Objective Function" sub-registry:

   Value      Description                        Reference
   (TBD1)     MSL                                [This I.D.]
   (TBD2)     MSN                                [This I.D.]
   (TBD3)     MSS                                [This I.D.]


8.  Acknowledgments

   We would like to thank Adrian Farrel for pointing out the need for
   this document.

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>.

   [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>.

   [RFC5541]  Le Roux, JL., Vasseur, JP., and Y. Lee, "Encoding of
              Objective Functions in the Path Computation Element
              Communication Protocol (PCEP)", RFC 5541,
              DOI 10.17487/RFC5541, June 2009,
              <http://www.rfc-editor.org/info/rfc5541>.

9.2.  Informative References







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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>.

   [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,
              DOI 10.17487/RFC5441, April 2009,
              <http://www.rfc-editor.org/info/rfc5441>.

   [RFC5521]  Oki, E., Takeda, T., and A. Farrel, "Extensions to the
              Path Computation Element Communication Protocol (PCEP) for
              Route Exclusions", RFC 5521, DOI 10.17487/RFC5521, April
              2009, <http://www.rfc-editor.org/info/rfc5521>.

   [RFC6006]  Zhao, Q., Ed., King, D., Ed., Verhaeghe, F., Takeda, T.,
              Ali, Z., and J. Meuric, "Extensions to the Path
              Computation Element Communication Protocol (PCEP) for
              Point-to-Multipoint Traffic Engineering Label Switched
              Paths", RFC 6006, DOI 10.17487/RFC6006, September 2010,
              <http://www.rfc-editor.org/info/rfc6006>.

   [RFC6805]  King, D., Ed. and A. Farrel, Ed., "The Application of the
              Path Computation Element Architecture to the Determination
              of a Sequence of Domains in MPLS and GMPLS", RFC 6805,
              DOI 10.17487/RFC6805, November 2012,
              <http://www.rfc-editor.org/info/rfc6805>.

   [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.dwpz-pce-domain-diverse]
              Dhody, D., Wu, Q., Palle, U., and X. Zhang, "PCE support
              for Domain Diversity", draft-dwpz-pce-domain-diverse-06
              (work in progress), October 2016.











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Appendix A.  Contributor Addresses

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

   EMail: zhang.xian@huawei.com

   Udayasree Palle
   Huawei Technologies
   Divyashree Techno Park, Whitefield
   Bangalore, Karnataka  560066
   India

   EMail: udayasreereddy@gmail.com

   Avantika
   Huawei Technologies
   Divyashree Techno Park, Whitefield
   Bangalore, Karnataka  560066
   India

   EMail: s.avantika.avantika@gmail.com

Appendix B.  Example

   This section illustrate an example based on SRLG.


       (1)       (2)       (3)
   A---------B---------C---------D
   |         |         |         |
   |      (2)|      (5)|         |
   |         |         |         |
   +---------E---------F---------+
       (4)       (2)        (5)

   Node A is Ingress, Node D is Egress.  A synchronized path computation
   requests for SRLG disjoint path may be issued using the SVEC object
   as described in [RFC5440].  In above topology a full SRLG disjoint
   paths are not possible because of some topology considerations.

   In such scenario, an OF MSS maybe used instead to minimize the number
   of shared (common) SRLG to get maximum diversity when full diversity
   may not be possible.




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   In case of sequential non-synchronized path computation, primary path
   will be computed first, say the path is (A--B--C--D) with SRLG list
   (1,2,3).  A backup path computation using XRO and SRLG sub-object
   with X bit (loose) set as 1, can be used to achieve a similar result.

Authors' Addresses

   Dhruv Dhody
   Huawei Technologies
   Divyashree Techno Park, Whitefield
   Bangalore, Karnataka  560066
   India

   EMail: dhruv.ietf@gmail.com


   Qin Wu
   Huawei Technologies
   101 Software Avenue, Yuhua District
   Nanjing, Jiangsu  210012
   China

   EMail: bill.wu@huawei.com




























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