Troubleshooting guide

Troubleshooting OSPF
7-115
ABR Configured Without Area 0 Interface
If there are two or more OSPF networks, both should be configured with a different
area ID, and at least one OSPF network must have an area ID of 0.
Follow these steps to configure an OSPF Area Border Router (ABR) with an Area 0
interface:
1. To verify that at least one ABR exists for the area, use the show running-config
command in Privileged EXEC mode on OSPF routers. ABRs must belong to area
0, which is the OSPF backbone and one other area. Look for network statements
that indicate that the router is part of area 0.
2. To define the interfaces on which OSPF runs and to define the area ID for those
interfaces, use the network area command in Router Configuration mode, as
shown in the following example:
RDN(config)#router ospf
RDN(config-ospf)#router ospf network <address><wildcard-mask> area
<area-id>
Table 7-1 describes the command options that are available for the network area
command:
Note: Ensure that at least one OSPF network is defined as area 0.
Table 7-1 router ospf network area Command Options
Command Option Description
address IP address of the OSPF interface.
wildcard-mask IP-address-type mask that includes don’t care bits.
area-id Area that is associated with the OSPF address range. It can
be specified as either a decimal value or as an IP address. If
you intend to associate areas with IP subnets, you can specify
a subnet address as the area-id.