Avaya Configuring IP, ARP, RIP, and OSPF Services Uživatelský manuál stáhnout pdf (Strana 223)

Customizing OSPF Services

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By definition, a border router has an interface to the backbone and interfaces to

one or more other areas. To configure OSPF as a border router:

Assign the backbone ID (0.0.0.0) to an OSPF interface.

Assign an area ID to another OSPF interface.

Configuring a Virtual Backbone Link Through a Transit Area

Every border router must have a connection to the backbone. This connection can

be physical or virtual.

If the border router has an interface to a backbone network, that router is

considered to be physically connected to the backbone. In Figure 6-5

, border

router 1 and border router 2 are both physically connected to the backbone.

In some cases, it may not be possible to configure a border router with an interface

to a backbone network. If the router has an OSPF neighbor that is physically

connected to the backbone, the router can use that neighbor to establish a virtual

link to the backbone.

In Figure 6-6

, for example, border router 1 has lost its interface to the backbone

network. In its place, the network administrator has configured an interface to a

network in area B. Through this network, border router 1 now has a neighbor --

border router 2 -- that is connected physically to the backbone. The network

administrator can use border router 2 to configure a virtual link between border

router 1 and the backbone.

An area that provides a virtual link between a border router and the backbone is

called a transit area. In Figure 6-6

, area B functions as a transit area.

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Avaya Configuring IP, ARP, RIP, and OSPF Services Uživatelský manuál Strana 223