Configuring OSPF
139
no fair-queue
!
interface Serial1
ip address 172.16.20.1 255.255.255.0
no ip directed-broadcast
clockrate 2000000
dce-terminal-timing-enable
!
interface Serial2
no ip address
no ip directed-broadcast
shutdown
!
interface Serial3
no ip address
no ip directed-broadcast
shutdown
!
interface BRI0
no ip address
no ip directed-broadcast
shutdown
!
router ospf 1
network 172.16.10.6 0.0.0.0 area 0
network 172.16.20.0 0.0.0.255 area 0
!
As you can see, these are very simple, straightforward configurations. All
interfaces are assigned to Area 0. Another interesting fact about creating a
single area is that there are no ABRs or ASBRs. It is possible to have an ASBR
without having an ABR. If external routes are injected into the area, the
router injecting them will be considered an ASBR. In order to activate an
ABR, any interface on the router must be assigned to a different area.
It is also important to recognize that the neighbor discovery was auto-
matic in this single-area configuration. Now let's move on to an environment
where sometimes neighbors must be configured manually.
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