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Configuring OSPFv3 OSPFv3 Overview
OmniSwitch 6800/6850/9000 Advanced Routing Configuration Guide December 2007 page 2-9
OSPFv3 Areas
OSPFv3 allows collections of contiguous networks and hosts to be grouped together as an area. Each area
runs a separate copy of the basic link-state routing algorithm (usually called SPF). This means that each
area has its own topological database, as explained in the previous section.
OSPFv3 Intra-Area and Inter-Area Routing
An area’s topology is visible only to the members of the area. Conversely, routers internal to a given area
know nothing of the detailed topology external to the area. This isolation of knowledge enables the proto-
col to reduce routing traffic by concentrating on small areas of an AS, as compared to treating the entire
AS as a single link-state domain.
Each router that participates in a specific area maintains an LSDB containing topological information for
that area. If the router participates in multiple areas, then it will maintain a separate database for each area
to which the router belongs. LSAs are flooded throughout an area to ensure that all participating routers
have an identical LSDB for that area.
A router connected to multiple areas is identified as an area border router (ABR). All ABRs must also
belong to a backbone area (also known as area 0). The backbone is responsible for distributing routing
information between areas. Although the backbone is an area itself, it consists of area border routers and
must also have links to all areas to which it will transfer information.The topology of the backbone area is
invisible to each of the areas, while the backbone itself knows nothing of the topology of the areas.
All routers in an area must agree on that area’s parameters. Since a separate copy of the link-state algo-
rithm is run in each area, most configuration parameters are defined on a per-router basis. All routers
belonging to an area must agree on that area’s configuration. Misconfiguration will keep neighbors from
forming adjacencies between themselves, and OSPFv3 will not function.
Inter-Area Routing
Backbone
Intra-Area
Routing
Intra-Area
Routing
Router 1
Router 2
Router 3
Router 4
Link State
Messages
Link State
Messages
Area 1
Area 2