How to configure OSPF Default Route

With OSPF it is no problem to configure a default route. There are a couple of options if you want to do this. Here’s an example:

R1(config)#router ospf 1  
R1(config-router)#default-information originate ?
  always       Always advertise default route
  metric       OSPF default metric
  metric-type  OSPF metric type for default routes
  route-map    Route-map reference
  <cr>

There are a number of things. We can change the metric or metric type but the most important thing most people forget is the always keyword.

If you use the default-information originate you can advertise a default route in OSPF. OSPF won’t advertise a default route if you don’t already have it in your routing table. If you add the always keyword it will advertise the default route even if you don’t have it in the routing table. Once you have advertised the default route it will look like this on other routers:

R2#show ip ospf database | begin Type-5
		Type-5 AS External Link States

Link ID         ADV Router      Age         Seq#       Checksum Tag
0.0.0.0         172.16.3.1      59          0x80000001 0x008D64 1

R2#show ip route ospf 
O*E2 0.0.0.0/0 [110/1] via 192.168.12.1, 00:00:24, FastEthernet0/0

It will show up as a LSA type 5 external route.

hostname R1
!
interface FastEthernet0/1
 ip address 192.168.12.1 255.255.255.0
!
router ospf 1
 network 192.168.12.0
 default-information originate always
!
end

hostname R2
!
interface FastEthernet0/1
 ip address 192.168.12.2 255.255.255.0
!
router ospf 1
 network 192.168.12.0
!
end