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




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.

本文档为互联网社区定义了一个实验协议。本文件是互联网工程任务组(IETF)的产品。它代表了IETF社区的共识。它已经接受了公众审查,并已被互联网工程指导小组(IESG)批准出版。并非IESG批准的所有文件都适用于任何级别的互联网标准;见RFC 5741第2节。

Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at


Copyright Notice


Copyright (c) 2013 IETF Trust and the persons identified as the document authors. All rights reserved.

版权所有(c)2013 IETF信托基金和确定为文件作者的人员。版权所有。

This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents ( 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.

本文件受BCP 78和IETF信托有关IETF文件的法律规定的约束(自本文件出版之日起生效。请仔细阅读这些文件,因为它们描述了您对本文件的权利和限制。从本文件中提取的代码组件必须包括信托法律条款第4.e节中所述的简化BSD许可证文本,并提供简化BSD许可证中所述的无担保。

1. Introduction
1. 介绍

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 MDR的主要责任是使链接状态广告(LSA)泛滥。备份MDR在MDR暂时失败时提供备份泛洪。

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.

o MDR允许通过要求仅在MDR/BMDR路由器及其邻居之间形成邻接来显著减少邻接的数量。

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 MDR和BMDR是根据从邻居收到的修改过的Hello数据包中获得的信息来选择的。

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 如果使用邻接减少(默认),则在MDR之间形成邻接,以形成连通子图。选项(AdjConnectivity=2)允许在MDR/BMDR之间形成额外的邻接,以生成双连通子图。

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.

o 每个非MDR路由器与称为其父级的MDR相邻,并且可选地(如果AdjConnectivity=2)与另一个称为其备份父级的MDR或BMDR相邻。

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

o 每个路由器在其路由器LSA中以点对点链路的形式播发到其相邻路由器的连接。不使用网络LSA。

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 除了全拓扑LSA之外,部分拓扑LSA还可用于减小路由器LSA的大小。这样的LSA被格式化为标准LSA,但只向邻居的子集发布链接。

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

o 或者,可以使用差分hello,它通过只报告相邻状态中的更改来减少开销。

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 (one-hop) neighbor of each other router. An understanding of [RFC5614] is assumed. Unlike an OSPF broadcast interface, such an interface can have a different cost associated with each neighbor. An example use case is when the underlying radio system performs layer-2 routing but has a different number of (layer-2) hops to (layer-3) neighbors.


The rationale for using this interface type for single-hop broadcast networks, instead of a broadcast interface type, is to represent the underlying network in a point-to-multipoint manner, allowing each router to advertise different costs to different neighbors in its router-LSA. In this sense, this document shows how the OSPF-MDR interface type can be configured (and simplified if desired) to achieve the same goals as the OSPF Hybrid Broadcast and Point-to-Multipoint interface type [RFC6845].


Section 2 describes the operation of OSPF-MDR in a single-hop broadcast network with recommended parameter settings. Section 3 describes an alternative procedure that may be used to decide which neighbors on a single-hop broadcast network to advertise in the router-LSA. Section 4 describes a simplified version of the MDR selection algorithm for single-hop networks.


The alternative procedure of Section 3 and the simplified algorithm of Section 4 are optional and MUST NOT be used if it is possible for two routers in the network to be more than one hop from each other.


1.1. Terminology
1.1. 术语

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. Operation in a Single-Hop Broadcast Network
2. 单跳广播网络中的操作

When OSPF-MDR is used in a single-hop broadcast network, the following parameter settings and options (defined in [RFC5614]) should be used:


o AdjConnectivity SHOULD be equal to 2 (biconnected); this provides the smoothest transition when one router replaces another as MDR, since the set of adjacencies forms a biconnected network that remains connected during the transition.

o AdjConnectivity应等于2(双连接);当一个路由器替换另一个作为MDR时,这提供了最平滑的过渡,因为邻接集形成了一个在过渡期间保持连接的双连接网络。

o AdjConnectivity MAY be equal to 1 (uniconnected), resulting in a slightly less smooth transition, since adjacencies must be formed between the new MDR and all of its neighbors.

o 邻接连通性可能等于1(单连通),导致稍微不太平滑的过渡,因为必须在新MDR与其所有相邻MDR之间形成邻接。

o AdjConnectivity SHOULD NOT be equal to 0 (full topology), since this requires adjacencies to be formed between all pairs of routers, adding unnecessary message overhead.

o AdjConnectivity不应等于0(完整拓扑),因为这需要在所有路由器对之间形成邻接,从而增加不必要的消息开销。

o An adjacency SHOULD be eliminated if neither the router nor the neighbor is an MDR or BMDR (see Section 7.3 of [RFC5614]).

o 如果路由器和邻居都不是MDR或BMDR(参见[RFC5614]第7.3节),则应消除相邻关系。

o LSAFullness MUST be equal to 4 or 5 if full-topology LSAs are required. (The value 5 is defined in Section 3 of this document.)

o 如果需要全拓扑LSA,则LSAFULNESS必须等于4或5。(本文件第3节定义了值5。)

o LSAFullness MAY be equal to 1 (min-cost LSAs) if full-topology LSAs are not required. This option reduces the number of advertised links while still providing shortest paths.

o 如果不需要完整拓扑LSA,则LSAFULNESS可能等于1(最小成本LSA)。此选项可减少播发链接的数量,同时仍提供最短路径。

If AdjConnectivity equals 1 or 2 and full-topology LSAs are used, OSPF-MDR running on a single-hop broadcast network has the following properties:


o A single MDR is selected, which becomes adjacent with every other router, as in an OSPF broadcast network.

o 选择一个MDR,该MDR与其他路由器相邻,如在OSPF广播网络中。

o Two BMDRs are selected. This occurs because the MDR selection algorithm ensures that the MDR/BMDR backbone is biconnected. If AdjConnectivity = 2, every non-MDR/BMDR router becomes adjacent with one of the BMDRs in addition to the MDR.

o 选择了两个BMDR。这是因为MDR选择算法确保MDR/BMDR主干是双连接的。如果AdjConnectivity=2,则除MDR外,每个非MDR/BMDR路由器与其中一个BMDR相邻。

o When all adjacencies are fully adjacent, the router-LSA for each router includes point-to-point (type 1) links to all bidirectional neighbors (in state 2-Way or greater).

o 当所有邻接完全相邻时,每个路由器的路由器LSA包括指向所有双向邻接的点对点(类型1)链路(状态为双向或更高)。

3. Originating Router-LSAs
3. 始发路由器LSA

A router running OSPF-MDR with LSAFullness = 4 includes in its router-LSA point-to-point (type 1) links for all fully adjacent neighbors, and for all bidirectional neighbors that are routable. A neighbor is routable if the SPF calculation has produced a route to the neighbor and a flexible quality condition is satisfied.


This section describes an alternative procedure that MAY be used instead of the procedure described in Section 6 of [RFC5614], to decide which neighbors on a single-hop broadcast network to advertise in the router-LSA. The alternative procedure will correspond to LSAFullness = 5, and is interoperable with the other choices for LSAFullness. This procedure avoids the need to check whether a neighbor is routable, and thus avoids having to update the set of routable neighbors.


If LSAFullness = 5, then the Selected Advertised Neighbor Set (SANS) is the same as specified for LSAFullness = 4, and the following steps are performed instead of the first paragraph of Section 9.4 in [RFC5614].


(1) The MDR includes in its router-LSA a point-to-point (type 1) link for each fully adjacent neighbor. (Note that the MDR becomes adjacent with all of its neighbors.)

(1) MDR在其路由器LSA中为每个完全相邻的邻居提供点对点(1型)链路。(请注意,MDR将与其所有邻居相邻。)

(2) Each non-MDR router includes in its router-LSA a point-to-point link for each fully adjacent neighbor, and, if the router is fully adjacent with the MDR, for each bidirectional neighbor j such that the MDR's router-LSA includes a link to j.

(2) 每个非MDR路由器在其路由器LSA中包括针对每个完全相邻的邻居的点对点链路,并且,如果路由器与MDR完全相邻,则针对每个双向邻居j,使得MDR的路由器LSA包括到j的链路。

To provide rationale for the above procedure, let i and j be two non-MDR routers. Since the SPF calculation (Section 16.1 of [RFC2328]) allows router i to use router j as a next hop only if router j advertises a link back to router i, routers i and j must both advertise a link to each other in their router-LSAs before either can use the other as a next hop. Therefore, the above procedure for non-MDR routers (Step 2) implies there must exist a path of fully adjacent links between i and j (via the MDR) in both directions before this can happen. The above procedure for non-MDR routers is similar to one described in Section 4.6 of [RFC6845] for non-DR routers.


4. MDR Selection Algorithm
4. MDR选择算法

The MDR selection algorithm of [RFC5614] simplifies as follows in single-hop networks. The resulting algorithm is similar to the DR election algorithm of OSPF, but is slightly different (e.g., two Backup MDRs are selected). The following simplified algorithm is interoperable with the full MDR selection algorithm.


Note that lexicographic order is used when comparing tuples of the form (RtrPri, MDR Level, RID). Also note that each router will form adjacencies with its Parents and dependent neighbors. In the following, the term "neighbor" refers to a bidirectional neighbor (in state 2-Way or greater).


Phase 1: Creating the neighbor connectivity matrix is not required.


Phase 2: MDR Selection


(2.1) The set of Dependent Neighbors is initialized to be empty.


(2.2) If the router has a larger value of (RtrPri, MDR Level, RID) than all of its (bidirectional) neighbors, the router selects itself as an MDR; selects its BMDR neighbors as Dependent Neighbors if AdjConnectivity = 2; then proceeds to Phase 4.


(2.3) Otherwise, if the router's MDR Level is currently MDR, then it is changed to BMDR before executing Phase 3.


Phase 3: Backup MDR Selection


(3.1) Let Rmax be the neighbor with the largest value of (RtrPri, MDR Level, RID).


(3.2) Determine whether or not there exist two neighbors, other than Rmax, with a larger value of (RtrPri, MDR Level, RID) than the router itself.


(3.3) If there exist two such neighbors, then the router sets its MDR Level to MDR Other.

(3.3)如果存在两个这样的邻居,则路由器将其MDR级别设置为MDR Other。

(3.4) Else, the router sets its MDR Level to BMDR, and if AdjConnectivity = 2, adds Rmax and its MDR/BMDR neighbors as Dependent Neighbors.


(3.5) If steps 3.1 through 3.4 resulted in the MDR Level changing from MDR Other to BMDR, then execute Step 2.2 again before proceeding to Phase 4. (This is necessary because running Step 2.2 again can cause the MDR Level to change to MDR.)

(3.5)如果步骤3.1至3.4导致MDR级别从MDR Other更改为BMDR,则在进入第4阶段之前,再次执行步骤2.2。(这是必要的,因为再次运行步骤2.2可能会导致MDR级别更改为MDR。)

Phase 4: Parent Selection


Each router selects a Parent and (if AdjConnectivity = 2) a Backup Parent for the single-hop broadcast network. The Parent for a non-MDR router will be the MDR. The Backup Parent for an MDR Other, if it exists, will be a BMDR. Each non-MDR router becomes adjacent with its Parent and its Backup Parent, if it exists. The Parent selection algorithm is already simple, so a simplified version is not given here.

每个路由器为单跳广播网络选择一个父节点和一个备份父节点(如果AdjConnectivity=2)。非MDR路由器的父级将是MDR。MDR Other的备份父级(如果存在)将是BMDR。每个非MDR路由器与其父路由器及其备份父路由器(如果存在)相邻。父选择算法已经很简单,因此这里不提供简化版本。

The Parent and Backup Parent are analogous to the Designated Router and Backup Designated Router interface data items in OSPF. As in OSPF, these are advertised in the DR and Backup DR fields of each Hello sent on the interface.

父级和备份父级类似于OSPF中的指定路由器和备份指定路由器接口数据项。与在OSPF中一样,在接口上发送的每个Hello的DR和Backup DR字段中都会公布这些信息。

5. Security Considerations
5. 安全考虑

This document describes the use of OSPF-MDR in a single-hop broadcast network, and raises no security issues in addition to those already covered in [RFC5614].


6. Normative References
6. 规范性引用文件

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

[RFC2119]Bradner,S.,“RFC中用于表示需求水平的关键词”,BCP 14,RFC 2119,1997年3月。

[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998.

[RFC2328]Moy,J.,“OSPF版本2”,STD 54,RFC 2328,1998年4月。

[RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF for IPv6", RFC 5340, July 2008.

[RFC5340]Coltun,R.,Ferguson,D.,Moy,J.,和A.Lindem,“IPv6的OSPF”,RFC 53402008年7月。

[RFC5614] Ogier, R. and P. Spagnolo, "Mobile Ad Hoc Network (MANET) Extension of OSPF Using Connected Dominating Set (CDS) Flooding", RFC 5614, August 2009.

[RFC5614]Ogier,R.和P.Spagnolo,“使用连接支配集(CDS)泛洪的OSPF移动自组织网络(MANET)扩展”,RFC 5614,2009年8月。

7. Informative References
7. 资料性引用

[RFC6845] Sheth, N., Wang, L., and J. Zhang, "OSPF Hybrid Broadcast and Point-to-Multipoint Interface Type", RFC 6845, January 2013.

[RFC6845]Sheth,N.,Wang,L.,和J.Zhang,“OSPF混合广播和点对多点接口类型”,RFC 68452013年1月。

Author's Address


Richard G. Ogier EMail:

Richard G.Ogier电子邮件