Use of OSPF-MDR in Single-Hop Broadcast Networks
RFC 7038

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Internet Engineering Task Force (IETF)                          R. Ogier
Request for Comments: 7038                             SRI International
Updates: 5614                                               October 2013
Category: Experimental
ISSN: 2070-1721

            Use of OSPF-MDR in Single-Hop Broadcast Networks

Abstract

   RFC 5614 (OSPF-MDR) extends OSPF to support mobile ad hoc networks
   (MANETs) by specifying its operation on the new OSPF interface of
   type MANET.  This document describes the use of OSPF-MDR (MANET
   Designated Router) in a single-hop broadcast network, which is a
   special case of a MANET in which each router is a (one-hop) neighbor
   of each other router.  Unlike an OSPF broadcast interface, such an
   interface can have a different cost associated with each neighbor.
   The document includes configuration recommendations and simplified
   mechanisms that can be used in single-hop broadcast networks.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for examination, experimental implementation, and
   evaluation.

   This document defines an Experimental Protocol for the Internet
   community.  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).  Not
   all documents approved by the IESG are a candidate for any level of
   Internet Standard; see 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/rfc7038.

Ogier                         Experimental                      [Page 1]
RFC 7038        OSPF-MDR in Single-Hop Broadcast Networks   October 2013

Copyright Notice

   Copyright (c) 2013 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
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

1.  Introduction

   OSPF-MDR [RFC5614] specifies an extension of OSPF [RFC2328, RFC5340]
   to support mobile ad hoc networks (MANETs) by specifying its
   operation on the new OSPF interface of type MANET.  OSPF-MDR
   generalizes the Designated Router (DR) to a connected dominating set
   (CDS) consisting of a typically small subset of routers called MANET
   Designated Routers (MDRs).  Similarly, the Backup Designated Router
   (BDR) is generalized to a subset of routers called Backup MDRs
   (BMDRs).  MDRs achieve scalability in MANETs similar to the way DRs
   achieve scalability in broadcast networks:

   o  MDRs have primary responsibility for flooding the Link State
      Advertisements (LSAs). Backup MDRs provide backup flooding when
      MDRs temporarily fail.

   o  MDRs allow the number of adjacencies to be dramatically reduced by
      requiring adjacencies to be formed only between MDR/BMDR routers
      and their neighbors.

   In addition, OSPF-MDR has the following features:

   o  MDRs and BMDRs are elected based on information obtained from
      modified Hello packets received from neighbors.

   o  If adjacency reduction is used (the default), adjacencies are
      formed between MDRs so as to form a connected subgraph.  An option
      (AdjConnectivity = 2) allows for additional adjacencies to be
      formed between MDRs/BMDRs to produce a biconnected subgraph.

   o  Each non-MDR router becomes adjacent with an MDR called its
      Parent, and optionally (if AdjConnectivity = 2) becomes adjacent
      with another MDR or BMDR called its Backup Parent.

Ogier                         Experimental                      [Page 2]
RFC 7038        OSPF-MDR in Single-Hop Broadcast Networks   October 2013

   o  Each router advertises connections to its neighbor routers as
      point-to-point links in its router-LSA.  Network-LSAs are not
      used.

   o  In addition to full-topology LSAs, partial-topology LSAs may be
      used to reduce the size of router-LSAs.  Such LSAs are formatted
      as standard LSAs, but advertise links to only a subset of
      neighbors.

   o  Optionally, differential Hellos can be used, which reduce overhead
      by reporting only changes in neighbor states.

   This document describes the use of OSPF-MDR in a single-hop broadcast
   network, which is a special case of a MANET in which each router is a