Thursday, November 20, 2008

OSPF routing part VIII - Conditional default route

In the above scenario R3 must only advertise a default route to F4 if its connection to BB2 is up.

This can be achieved by making use of conditional default route advertisement feature. This requires use of a route-map to indicate those routes that must be available in the routing table before the default route will be advertised.

In his example

Rack1R3#show ip route inc 204.12C is directly connected, FastEthernet1/0

ip prefix-list BB2 permit

route-map CONNECTED permit 10

match ip address prefix-list BB2

router ospf 1

default-information originate route-map CONNECTED

Once the config is applied on R3 the default route pops up on R4.

Rack1R4#sir inc 0.0.0

Gateway of last resort is to network*E2 [110/1] via, 00:16:22, Serial2/0

If i shut down the fa1/0 interface on R3 the default route dissapears from the routing table on R3 and subsequently the default route dissappears from R4 routing table as well.

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