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Chapter 4
OSPF Areas
F I G U R E 4 . 6
OSPF area topology
Only two of the five configurations are shown--otherwise you would just
see a lot of redundant information. Notice the very specific wildcard masks
in the network statements. These facilitate the removal or addition of spe-
cific links when troubleshooting. If you have a link that is flapping, you can
easily remove it so that it does not cause LSA flooding within the area. After
the link has stabilized, it will be very easy to add the interface back in.
For example, if all of the router's interfaces could be summarized by a net-
work statement of, then you would need only one
network statement to add all interfaces to the OSPF process. However, if one
out of the many interfaces was flapping, you could not easily isolate that
interface so that it would not cause unnecessary LSA flooding. Let's examine
the IOS configuration for this topology:
RouterA#show running-config
Building configuration...
Current configuration:
version 11.2
no service password-encryption
no service udp-small-servers
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