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Totally Stubby Area Configuration

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networks. By using these summary routes where possible, we can reduce the
size of a router's routing tables, thus lowering memory and processor overhead.

We will also use the 10.0.0.0/8 summary when we configure RouterC and

RouterD. Remember that it is critical that all routers that are members of a
stub area be configured as stubby for that area. Therefore, RouterC and
RouterD will have identical OSPF configurations:

RouterC(config)#router ospf 10

RouterC(config-router)#network 10.0.0.0 0.255.255.255 area

RouterC(config-router)#area 25 stub

RouterD(config)#router ospf 10

RouterD(config-router)#network 10.0.0.0 0.255.255.255 area

RouterD(config-router)#area 25 stub

Let's review some key elements of our stub area configuration example:

The syntax to make a router stubby is area area-id stub.

All routers that are part of Area 25 are configured as stubby.

Area 25 has only one ABR (i.e., only one path out of the area).

The ABR used the area area-id stub command only for Area 25,
not for Area 0, which is not stubby.

Totally Stubby Area Configuration

sing the same network topology as we had for the stub area config-

uration, let's examine how to make Area 25 a totally stubby area. Remem-
bering that the difference between a stub area and a totally stubby area is
that a totally stubby area doesn't have summary routes injected into it, we
only need to change the configuration of RouterB. Since RouterB is the ABR,
it is the router that will have the responsibility for blocking summary routes
from entering the stub area. So, again consider our network, as illustrated in
Figure 5.5.

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