Configuring OSPF
135
OSPF: Elect DR 172.16.240.1
DR: 172.16.240.1 (Id) BDR: none
OSPF: Build router LSA for area 0, router ID 172.16.240.1
We end the output here, because we know that once adjacencies have
been established, the link-state databases must synchronize during the
Exchange state and the transfer of DBD packets containing LSA updates.
Of interest in this output is the election of the DR and BDR. Initially, the
value for the BDR was 0.0.0.0. This was the first router on the network to
become active. Therefore, the first election to take place is that of BDR,
because Ethernet 0 is the only active OSPF interface at the moment, and the
Router ID of 172.16.240.1 (the loopback 0 IP address) is chosen to be the BDR.
When the process goes on to elect the DR, the only router capable is itself.
The role of DR is taken by 172.16.240.1, and the BDR is reset to 0.0.0.0
because there are no other routers active on this multi-access network.
No new commands were used to create this output. The only difference
was that the network 172.16.230.0 was configured on a broadcast multi-
access network.
Configuring OSPF--Single Area
The easiest (and least scalable) way to configure OSPF is to simply use Area 0.
If all you want to configure is one area, it must be Area 0. Creating a single
backbone area makes it easy to understand what OSPF is doing, but once
you get a number of routers in the area with all the interfaces assigned to
Area 0, processing time is going to be much greater and convergence slower.
To start learning, however, a single area is the perfect place to start. You
have already seen the command that is used for assigning an interface to an
area. Let's look at the configuration of a few routers to get a good feeling for
how it is done. Figure 4.6 depicts the physical layout of a test network.
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