OSPF over an NBMA Network

Another design consideration is the design of the NBMA network as part of the OSPF domain.

There are two main ways to approach the inclusion of an NBMA network:

• The NBMA network can be created as Area 0. The reasoning is that if the NBMA is used to connect all remote sites, all traffic will have to traverse this network. If the remote sites are made satellite areas, then all traffic will have to traverse the NBMA, so it makes sense to make it the backbone area. This works well in a full-mesh environment, although it will result in a large number of LSAs being flooded into the WAN and puts extra demands on the routers connecting to the NBMA network.

• In a hub-and-spoke NBMA network, it makes sense to assign the hub network as Area 0 with the other remote sites and the NBMA network as other areas. This is a good design if the satellite areas are stub areas because it means that the routing information—and, thus, network overhead—is kept to a minimum over the NBMA cloud. Depending on the design, the rest of the network may constitute one other area or multiple areas. This will depend on the size and growth expectations of the OSPF domain.

After the design of the network is in place, it is time to configure the routers. The configuration of a basic OSPF network is demonstrated in Chapter 5, "Using OSPF in a Single Area".

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