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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 DomainConfigure 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)
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 VerificationVerify 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:
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