    Internet Engineering Task Force (IETF)                       C. Dearlove
    Request for Comments: 7187                               BAE Systems ATC
    Updates: 7181                                                 T. Clausen
    Category: Standards Track                       LIX, Ecole Polytechnique
    ISSN: 2070-1721                                               April 2014

                   Routing Multipoint Relay Optimization for
          the Optimized Link State Routing Protocol Version 2 (OLSRv2)

    Abstract

       This specification updates the Optimized Link State Routing Protocol
       version 2 (OLSRv2) with an optimization to improve the selection of
       routing multipoint relays.  The optimization retains full
       interoperability between implementations of OLSRv2 with and without
       this optimization.

    Status of This Memo

       This is an Internet Standards Track document.

       This document is a product of the Internet Engineering Task Force
       (IETF).  It represents the consensus of the IETF community.  It has
       received public review and has been approved for publication by the
       Internet Engineering Steering Group (IESG).  Further information on
       Internet Standards is available in Section 2 of RFC 5741.

       Information about the current status of this document, any errata,
       and how to provide feedback on it may be obtained at
       http://www.rfc-editor.org/info/rfc7187.

    Copyright Notice

       Copyright (c) 2014 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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       publication of this document.  Please review these documents
       carefully, as they describe your rights and restrictions with respect
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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.

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    RFC 7187             OLSRv2 Routing MPR Optimization          April 2014

    Table of Contents

       1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
       2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   2
       3.  Applicability Statement . . . . . . . . . . . . . . . . . . .   2
       4.  Routing MPR Selection . . . . . . . . . . . . . . . . . . . .   3
       5.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
       6.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   4
       7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   4
         7.1.  Normative References  . . . . . . . . . . . . . . . . . .   4
         7.2.  Informative References  . . . . . . . . . . . . . . . . .   4

    1.  Introduction

       The Optimized Link State Routing Protocol version 2 [RFC7181] is a
       proactive link state routing protocol designed for use in mobile ad
       hoc networks (MANETs) [RFC2501].  This document improves one area of
       the OLSRv2 specification.

       One improvement included in OLSRv2, compared to its predecessor
       described in [RFC3626], is the use of link metrics, rather than
       minimum-hop routing.  A rationale for how link metrics were included
       in OLSRv2 is documented in [RFC7185].  However, one aspect of the use
       of link metrics described in [RFC7185], the removal of some
       unnecessarily selected routing multipoint relays (MPRs), was not
       included in [RFC7181].  This specification updates OLSRv2 to include
       this optimization.

       Note that this optimization does not impact interoperability:
       implementations that do and do not implement this optimization will
       interoperate seamlessly.

    2.  Terminology

       The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
       "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
       "OPTIONAL" in this document are to be interpreted as described in
       [RFC2119].

       Additionally, this document uses the terminology of [RFC7181].

    3.  Applicability Statement

       This specification updates [RFC7181].  As such, it is applicable to
       all implementations of this protocol.  The optimization presented in
       this specification is simply permissive; it allows an additional
       optimization, and there is no requirement for any implementation to

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    RFC 7187             OLSRv2 Routing MPR Optimization          April 2014

       include it.  However, inclusion of this optimization is advised; it
       can, in some cases, create smaller and fewer messages, without ever
       having the opposite effect.

       [RFC7181] defines the properties for the selection of routing MPRs
       from among a router's symmetric 1-hop neighbors.  The properties are

       o  the selected MPRs must consist of a set of symmetric 1-hop
          neighbors that cover all the symmetric 2-hop neighbors, and

       o  the selected MPRs must do so retaining a minimum distance route
          (1-hop, if present, or 2-hop) to each symmetric 2-hop neighbor.

       The discussion in the latter part of Section 6.2 of [RFC7185]
       indicates that this requirement is overly prescriptive for routing
       MPR selection.  The update to [RFC7181] described in this
       specification permits a router to use the described optimization,
       while still being considered compliant with OLSRv2.

       Note that whether or not a router is considered compliant, a router
       that implements the optimization described in this specification will
       interoperate successfully with routers that are not implementing this
       optimization.

    4.  Routing MPR Selection

       A set of routing MPRs created as specified in [RFC7181] MAY be
       optimized in the following manner.  Note that this uses the notation
       of Section 18.2 of [RFC7181]:

       1.  If there is a sequence x_0, ..., x_n of elements of N1 such that:

           *  x_0 is a routing MPR,

           *  x_1, ... , x_n have corresponding elements y_1, ..., y_n of
              N2, and

           *  d1(x_0) + d2(x_0,y_1) + ... + d2(x_m-1,y_m) < d1(x_m) for m =
              1, ... , n,

           then x_1 to x_n may be removed from the set of routing MPRs, if
           selected.

       Note that "corresponding elements" in N1 and N2 means that these
       elements represent the same router.  All of this information is
       available from information gathered by NHDP [RFC6130].

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    5.  Security Considerations

       The update to OLSRv2 [RFC7181] does not introduce any new protocol
       signals, nor does it change the processing of any received protocol
       signals.

       This update to OLSRv2 [RFC7181] permits an implementation that is
       compliant with OLSRv2 to (potentially) eliminate some unneeded
       routers from the routing MPR sets generated as described in
       [RFC7181], which also eliminates the need to include the
       corresponding information in generated Topology Control (TC)
       messages.  Because this information is not used when included, this
       update to OLSRv2 [RFC7181] does not present any additional security
       considerations, beyond those described in [RFC7181].

    6.  Acknowledgments

       The authors would like to gratefully acknowledge Philippe Jacquet
       (Alcatel-Lucent) for intense technical discussions and comments.

    7.  References

    7.1.  Normative References

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

       [RFC6130]  Clausen, T., Dean, J., and C. Dearlove, "Mobile Ad Hoc
                  Network (MANET) Neighborhood Discovery Protocol (NHDP)",
                  RFC 6130, April 2011.

       [RFC7181]  Clausen, T., Dearlove, C., Jacquet, P., and U. Herberg,
                  "The Optimized Link State Routing Protocol Version 2", RFC
                  7181, April 2014.

    7.2.  Informative References

       [RFC2501]  Macker, J. and S. Corson, "Mobile Ad hoc Networking
                  (MANET): Routing Protocol Performance Issues and
                  Evaluation Considerations", RFC 2501, January 1999.

       [RFC3626]  Clausen, T. and P. Jacquet, "The Optimized Link State
                  Routing Protocol", RFC 3626, October 2003.

       [RFC7185]  Clausen, T., Dearlove, C., and P. Jacquet, "Rationale for
                  the Use of Link Metrics in the Optimized Link State
                  Routing Protocol Version 2 (OLSRv2)", RFC 7185, April
                  2014.

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    RFC 7187             OLSRv2 Routing MPR Optimization          April 2014

    Authors' Addresses

       Christopher Dearlove
       BAE Systems Advanced Technology Centre
       West Hanningfield Road
       Great Baddow, Chelmsford
       United Kingdom

       Phone: +44 1245 242194
       EMail: chris.dearlove@baesystems.com
       URI:   http://www.baesystems.com/

       Thomas Heide Clausen
       LIX, Ecole Polytechnique

       Phone: +33 6 6058 9349
       EMail: T.Clausen@computer.org
       URI:   http://www.ThomasClausen.org/

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