4-1 default-information originate

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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 only advertise the default route if the route exists in the local IP routing table.

Initial Cisco IOS Software Release: 10.0

Configuration Example: Advertising a Default Route into the OSPF Domain

Configure the routers in Figure 4-1 as shown in the following code.

Figure 4-1. When OSPF Advertises a Default Route the Advertising Router Becomes an Autonomous System Border Router (ASBR)

graphics/04fig01.gif

 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 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   

Inspect the routing table on Router A to see if the default route is being advertised.

 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 not set      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, 00:05:30, Ethernet0/0      172.16.0.0/24 is subnetted, 1 subnets C       172.16.1.0 is directly connected, Ethernet0/0 

Router B is not advertising the default route because there is not a default route in the routing table on Router B. Configure a static default route on Router B. Once the static route is configured, then Router B should advertise the default route to Router A.

 Router B  ip route 0.0.0.0 0.0.0.0 Serial1  
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 0.0.0.0 to network 0.0.0.0  1.0.0.0/32 is subnetted, 1 subnets O       1.1.1.1 [110/11] via 172.16.1.1, 00:09:15, 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  S*   0.0.0.0/0 is directly connected, Serial1  

Verify that the 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:
Step 1. Verify that there is a neighbor relationship between the OSPF routers using the show ip ospf neighbors command.

Step 2. Verify that the router that is to advertise the default route has a default route in the IP routing table.

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Cisco[r] OSPF Command and Configuration Handbook
Cisco OSPF Command and Configuration Handbook (paperback)
ISBN: 1587055406
EAN: 2147483647
Year: 2002
Pages: 236

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