4-2 default-information originate always

Syntax Description:

This form of the command has no arguments.

Purpose: To enable OSPF to advertise the default route 0.0.0.0 into the OSPF domain. This form of the command will advertise the default route even if the route does not exist in the local IP routing table. If the always keyword is not used and the default route is flapping, then OSPF needs to send an update into the OSPF domain every time the route flaps. Using the always keyword will minimize OSPF database activity if the default route is flapping.

Initial Cisco IOS Software Release: 10.0

Configuration Example: Unconditionally Advertising a Default Route into the OSPF Domain

Configure the routers in Figure 4-2 as shown in the following code.

Figure 4-2. When OSPF Advertises a Default Route, the Advertising Router Becomes an ASBR. The default-information-originate always Command Will Unconditionally Advertise a Default Route

 Router A  interface Loopback0   ip address 1.1.1.1 255.255.255.255   !   interface Ethernet0/0   ip address 172.16.1.1 255.255.255.0   !   router ospf 1   network 1.1.1.1 0.0.0.0 area 0   network 172.16.1.0 0.0.0.255 area 0  ______________________________________________________________________________________ Router B  interface Loopback0   ip address 2.2.2.2 255.255.255.255   !   interface Ethernet0   ip address 172.16.1.2 255.255.255.0   !   interface Serial1   bandwidth 64   ip address 10.1.1.5 255.255.255.252   clockrate 64000   !   router ospf 1   network 2.2.2.2 0.0.0.0 area 0   network 172.16.1.0 0.0.0.255 area 0  

Verify that Routers A and B have established an OSPF neighbor relationship, as shown here.

 rtrA#  show ip ospf neighbor  Neighbor ID     Pri   State           Dead Time   Address         Interface 2.2.2.2           1   FULL/BDR        00:00:30    172.16.1.2      Ethernet0/0 ________________________________________________________________________________ rtrB#  show ip ospf neighbor  Neighbor ID     Pri   State           Dead Time   Address         Interface 1.1.1.1           1   FULL/DR         00:00:38    172.16.1.1      Ethernet0 

Modify the configuration on Router B so that OSPF will unconditionally advertise a default route into the OSPF domain.

 Router B  router ospf 1   network 2.2.2.2 0.0.0.0 area 0   network 172.16.1.0 0.0.0.255 area 0    default-information originate always   

Verification

Verify that the default route is in the IP routing table on Router B.

 rtrB#  show ip route  Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP        D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area        N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2        E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP        i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default        U - per-user static route, o - ODR Gateway of last resort is not set      1.0.0.0/32 is subnetted, 1 subnets O       1.1.1.1 [110/11] via 172.16.1.1, 16:23:59, Ethernet0      2.0.0.0/32 is subnetted, 1 subnets C       2.2.2.2 is directly connected, Loopback0      172.16.0.0/24 is subnetted, 1 subnets C       172.16.1.0 is directly connected, Ethernet0      10.0.0.0/30 is subnetted, 1 subnets C       10.1.1.4 is directly connected, Serial1 

Router B does not have a default route in the IP routing table. Verify that a default route is being advertised to Router A.

 rtrA#  show ip route  Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP        D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area        N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2        E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP        i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default        U - per-user static route, o - ODR  Gateway of last resort is 172.16.1.2 to network 0.0.0.0  1.0.0.0/32 is subnetted, 1 subnets C       1.1.1.1 is directly connected, Loopback0      2.0.0.0/32 is subnetted, 1 subnets O       2.2.2.2 [110/11] via 172.16.1.2, 00:10:27, Ethernet0/0      172.16.0.0/24 is subnetted, 1 subnets C       172.16.1.0 is directly connected, Ethernet0/0  O*E2 0.0.0.0/0 [110/1] via 172.16.1.2, 00:01:17, Ethernet0/0  

Troubleshooting

If there is an OSPF relationship between the OSPF routers, then this command should work as expected.