This document shows how Open Shortest Path First (OSPF) injects a default route into a normal area. Default routes injected into a normal area can be originated by any OSPF router. The OSPF router does not, by default, generate a default route into the OSPF domain. In order for OSPF to generate a default route, you must use the default-information originate command.
There are two ways to advertise a default route into a normal area. The first is to advertise 0.0.0.0 into the OSPF domain, provided the advertising router already has a default route. The second is to advertise 0.0.0.0 regardless of whether the advertising router already has a default route. The second method can be accomplished by adding the keyword always to the default-information originate command.
There are no specific requirements for this document.
This document is not restricted to specific software and hardware versions.
For more information on document conventions, see the Cisco Technical Tips Conventions.
In this section, you are presented with the information to configure the features described in this document.
This document uses the network setup shown in this diagram.
This document uses the configurations shown here.
Current configuration: hostname r188.8.131.52 interface Loopback0 ip address 184.108.40.206 255.0.0.0 interface Serial2/1/0 ip address 220.127.116.11 255.0.0.0 router ospf 2 network 18.104.22.168 0.255.255.255 area 1 end
Current configuration: hostname r22.214.171.124 interface Loopback0 ip address 126.96.36.199 255.0.0.0 interface Serial0/1/0 ip address 188.8.131.52 255.0.0.0 interface ATM1/0.20 ip address 184.108.40.206 255.0.0.0 router ospf 2 network 220.127.116.11 0.255.255.255 area 1 network 18.104.22.168 0.255.255.255 area 0 default-information originate ip route 0.0.0.0 0.0.0.0 22.214.171.124 end
This section provides information you can use to confirm your configuration is working properly.
show ip ospf database —Displays a list of the Link State Advertisements (LSAs) and types them into a link state database. This list shows only the information in the LSA header.
show ip ospf database external —Displays information only about the external LSAs.
show ip route —Displays the current status of the routing table.
This output displays how the OSPF database looks given this network environment, using the show ip ospf database command.
r126.96.36.199#show ip ospf database OSPF Router with ID (188.8.131.52) (Process ID 2) Router Link States (Area 0) Link ID ADV Router Age Seq# Checksum Link count 184.108.40.206 220.127.116.11 600 0x80000001 0x9583 1 Summary Net Link States (Area 0) Link ID ADV Router Age Seq# Checksum 18.104.22.168 22.214.171.124 600 0x80000001 0x8E61 Router Link States (Area 1) Link ID ADV Router Age Seq# Checksum Link count 126.96.36.199 188.8.131.52 864 0x8000005E 0xD350 2 184.108.40.206 220.127.116.11 584 0x8000001E 0xF667 2 Summary Net Link States (Area 1) Link ID ADV Router Age Seq# Checksum 18.104.22.168 22.214.171.124 585 0x80000004 0xA87C Type-5 AS External Link States Link ID ADV Router Age Seq# Checksum Tag 0.0.0.0 126.96.36.199 601 0x80000001 0xD0D8 0
Because it has a default route, Router 188.8.131.52 originates a type 5 LSA with a link ID of 0.0.0.0. This is the result of the default-information originate command in its OSPF configuration.
r184.108.40.206#show ip ospf database external 0.0.0.0 OSPF Router with ID (220.127.116.11) (Process ID 2) Type-5 AS External Link States LS age: 650 Options: (No TOS-capability, DC) LS Type: AS External Link Link State ID: 0.0.0.0 (External Network Number ) Advertising Router: 18.104.22.168 LS Seq Number: 80000001 Checksum: 0xD0D8 Length: 36 Network Mask: /0 Metric Type: 2 (Larger than any link state path) TOS: 0 Metric: 1 Forward Address: 0.0.0.0 External Route Tag: 0 r22.214.171.124#show ip route 0.0.0.0 S* 0.0.0.0/0 [1/0] via 126.96.36.199, 00:28:00, ATM1/0.20 r188.8.131.52#show ip route ospf O IA 184.108.40.206/8 [110/65] via 220.127.116.11, 00:00:18, Serial2/1/0 O*E2 0.0.0.0/0 [110/1] via 18.104.22.168, 00:00:18, Serial2/1/0
You can also add the always keyword to the default-information originate command to make a router originate a 0.0.0.0 type 5 LSA even if the router does not have a default route in its routing table.
There is currently no specific troubleshooting information available for this configuration.
The Cisco Support Community is a forum for you to ask and answer questions, share suggestions, and collaborate with your peers.
Refer to Cisco Technical Tips Conventions for information on conventions used in this document.