draft-ietf-ospf-manet-single-hop-mdr-03.txt   draft-ietf-ospf-manet-single-hop-mdr-04.txt 
Network Working Group R. Ogier Network Working Group R. Ogier
Internet-Draft SRI International Internet-Draft SRI International
Updates: 5614 June 3, 2013 Updates: 5614 August 7, 2013
Intended status: Experimental Intended status: Experimental
Expires: December 5, 2013 Expires: February 8, 2014
Use of OSPF-MDR in Single-Hop Broadcast Networks Use of OSPF-MDR in Single-Hop Broadcast Networks
draft-ietf-ospf-manet-single-hop-mdr-03.txt draft-ietf-ospf-manet-single-hop-mdr-04.txt
Abstract Abstract
RFC 5614 (OSPF-MDR) extends OSPF to support mobile ad hoc 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 (MANETs) by specifying its operation on the new OSPF interface of type
MANET. This document describes the use of OSPF-MDR in a single-hop MANET. 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 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 router is a (one-hop) neighbor of each other router. Unlike an OSPF
broadcast interface, such an interface can have a different cost broadcast interface, such an interface can have a different cost
associated with each neighbor. The document includes configuration associated with each neighbor. The document includes configuration
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o In addition to full-topology LSAs, partial-topology LSAs may be o In addition to full-topology LSAs, partial-topology LSAs may be
used to reduce the size of router-LSAs. Such LSAs are formatted used to reduce the size of router-LSAs. Such LSAs are formatted
as standard LSAs, but advertise links to only a subset of as standard LSAs, but advertise links to only a subset of
neighbors. neighbors.
o Optionally, differential Hellos can be used, which reduce o Optionally, differential Hellos can be used, which reduce
overhead by reporting only changes in neighbor states. overhead by reporting only changes in neighbor states.
This document describes the use of OSPF-MDR in a single-hop broadcast 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 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 (one-hop) neighbor of each other router. An understanding of
interface, such an interface can have a different cost associated [RFC5614] is assumed. Unlike an OSPF broadcast interface, such an
with each neighbor. An example use case is when the underlying radio interface can have a different cost associated with each neighbor.
system performs layer-2 routing, but has a different number of An example use case is when the underlying radio system performs
(layer-2) hops to (layer-3) neighbors. 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 The rationale for using this interface type for single-hop broadcast
networks, instead of a broadcast interface type, is to represent the networks, instead of a broadcast interface type, is to represent the
underlying network in a point-to-multipoint manner, allowing each underlying network in a point-to-multipoint manner, allowing each
router to advertise different costs to different neighbors in its router to advertise different costs to different neighbors in its
router-LSA. In this sense, this document shows how the OSPF-MDR router-LSA. In this sense, this document shows how the OSPF-MDR
interface type can be configured (and simplified if desired) to interface type can be configured (and simplified if desired) to
achieve the same goals as the OSPF Hybrid Broadcast and Point-to- achieve the same goals as the OSPF Hybrid Broadcast and Point-to-
Multipoint interface type [RFC6845]. Multipoint interface type [RFC6845].
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The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
2. Operation in a Single-Hop Broadcast Network 2. Operation in a Single-Hop Broadcast Network
When OSPF-MDR is used in a single-hop broadcast network, the When OSPF-MDR is used in a single-hop broadcast network, the
following parameter settings and options (defined in [RFC5614]) following parameter settings and options (defined in [RFC5614])
should be used: should be used:
o AdjConnectivity SHOULD be equal to 2 (biconnected), MAY be equal o AdjConnectivity SHOULD be equal to 2 (biconnected); this provides
to 1 (uniconnected), and SHOULD NOT be equal to 0 (full topology). the smoothest transition when one router replaces another as MDR,
since the set of adjacencies forms a biconnected network which
remains connected during the transition.
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 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 An adjacency SHOULD be eliminated if neither the router nor o An adjacency SHOULD be eliminated if neither the router nor
the neighbor is an MDR or BMDR (see Section 7.3 of [RFC5614]). the neighbor is an MDR or BMDR (see Section 7.3 of [RFC5614]).
o LSAFullness MUST be equal to 4 or 5 if full-topology LSAs are 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.) required. (The value 5 is defined in Section 3 of this document.)
o LSAFullness MAY be equal to 1 (min-cost LSAs) if full-topology o LSAFullness MAY be equal to 1 (min-cost LSAs) if full-topology
LSAs are not required. This option reduces the number of LSAs are not required. This option reduces the number of
advertised links while still providing shortest paths. advertised links while still providing shortest paths.
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(1) The MDR includes in its router-LSA a point-to-point (type 1) link (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 for each fully adjacent neighbor. (Note that the MDR becomes
adjacent with all of its neighbors.) adjacent with all of its neighbors.)
(2) Each non-MDR router includes in its router-LSA a point-to-point (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 link for each fully adjacent neighbor, and, if the router is
fully adjacent with the MDR, for each bidirectional neighbor j fully adjacent with the MDR, for each bidirectional neighbor j
such that the MDR's router-LSA includes a link to j. such that the MDR's router-LSA includes a link to j.
To provide rationale for the above procedure, let i and j be two To provide rationale for the above procedure, let i and j be two non-
non-MDR routers. Since the SPF calculation (Section 16.1 of MDR routers. Since the SPF calculation (Section 16.1 of [RFC2328])
[RFC2328]) allows router i to use router j as a next hop only if allows router i to use router j as a next hop only if router j
router j advertises a link back to router i, routers i and j must advertises a link back to router i, routers i and j must both
both advertise a link to each other in their router-LSAs before advertise a link to each other in their router-LSAs before either can
either can use the other as a next hop. Therefore, the above use the other as a next hop. Therefore, the above procedure for non-
procedure for non-MDR routers (Step 2) implies there must exist a MDR routers (Step 2) implies there must exist a path of fully
path of fully adjacent links between i and j (via the MDR) in adjacent links between i and j (via the MDR) in both directions
both directions before this can happen. The above procedure for before this can happen. The above procedure for non-MDR routers is
non-MDR routers is similar to one described in Section 4.6 of similar to one described in Section 4.6 of [RFC6845] for non-DR
[RFC6845] for non-DR routers. routers.
4. MDR Selection Algorithm 4. MDR Selection Algorithm
The MDR selection algorithm of [RFC5614] simplifies as follows in The MDR selection algorithm of [RFC5614] simplifies as follows in
single-hop networks. The resulting algorithm is similar to the DR single-hop networks. The resulting algorithm is similar to the DR
election algorithm of OSPF, but is slightly different (e.g., two election algorithm of OSPF, but is slightly different (e.g., two
Backup MDRs are selected). The following simplified algorithm is Backup MDRs are selected). The following simplified algorithm is
interoperable with the full MDR selection algorithm. interoperable with the full MDR selection algorithm.
Note that lexicographic order is used when comparing tuples of the Note that lexicographic order is used when comparing tuples of the
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