The network Command

The first command to consider is one that was dealt with in Chapter 5. The network command was explained in terms of identifying the interfaces that participated in the OSPF routing process. The command will now be used to identify not only the interfaces that are sending and receiving OSPF updates, but also the area in which they reside. This configuration is used on an ABR.

The following is the syntax for the OSPF network command:

network network number wildcard mask area area number

NOTE The area requested in the preceding syntax is the area in which the interface or interfaces configured with the network address reside.

Care must be taken now in the use of the wildcard mask. In a single-area configuration, all the interfaces are in the same area. The network commands just identify the network numbers in use. Therefore, they may be configured to the Internet number, as they are in IGRP and RIP. The only reason to be more specific would be to exclude some interfaces from the OSPF domain.

Figure 6-6 illustrates the example configuration that follows. Figure 6-6 The network Command

Figure 6-6 illustrates the example configuration that follows. Figure 6-6 The network Command

Example 6-1 shows two interfaces, each with a subnet of the same major network where the interfaces are placed into different areas. The network number has been subnetted into the last octet so that you can truly see the power and granularity of the wildcard mask at work.

Example 6-1 The network Command network 172.16.20.128 0.0.0.7 area 0 network 172.16.20.8 0.0.0.7 area 1

The need now to identify areas on an interface basis brings into use the other part of the command. Although the command itself is very simple, it adds complexity to the use of the mask. It is to be remembered that the network command follows the rule of a linked list. The order of the statements is important: The most specific should be stated first because the OSPF process will act on the first match that is found.

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