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Configuring Multiarea Adjacency in OSPFv2

By default, a single interface can belong to only one OSPF area. However, in some situations, you might want to configure an interface to belong to more than one area. Doing so allows the corresponding link to be considered an intra-area link in multiple areas and to be preferred over other higher-cost intra-area paths. For example, you configure an interface to belong to multiple areas with a high-speed backbone link between two area border routers to enable you to create multiarea adjacencies that belong to different areas.

Beginning with JUNOS Release 9.2, you can configure a logical interface to belong to more than one OSPF area. As defined in RFC 5185, OSPF Multi-Area Adjacency, the area border routers establish multiple adjacencies belonging to different areas over the same logical interface. Each multiarea adjacency is announced as a point-to-point unnumbered link in the configured area by the routers connected to the link. For each area, one of the logical interfaces is treated as primary, and the remaining interfaces that are configured for the area are designated as secondary.

To configure a secondary logical interface for an OSPF area, include the secondary statement:




area  area-id {



interface interface-name {

secondary;
}


}

Any logical interface not configured as a secondary interface for an area is treated as a primary interface for that area. A logical interface can be configured as primary interface only for one area. For any other area for which you configure the interface, you must configure it as a secondary interface.

Note: You cannot configure the secondary statement with the interface all statement. You also cannot configure as secondary an interface by its IP address.

For a list of hierarchy levels at which you can include the statement, see the statement summary section for this statement.

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