Verify OSPF Interfaces
Purpose
After you have verified that the LSP is down, and the cause is not in the physical, data link, or IP layer, check the routers in your network to determine that all relevant OSPF interfaces are configured correctly.
Action
To verify OSPF interfaces, enter the following commands from the ingress, transit, and egress routers:
Sample Output 1
user@R1> show ospf interface Interface State Area DR ID BDR ID Nbrs so-0/0/0.0 PtToPt 0.0.0.0 0.0.0.0 0.0.0.0 1 so-0/0/1.0 PtToPt 0.0.0.0 0.0.0.0 0.0.0.0 1 so-0/0/2.0 PtToPt 0.0.0.0 0.0.0.0 0.0.0.0 1 user@R3> show ospf interface Interface State Area DR ID BDR ID Nbrs so-0/0/0.0 PtToPt 0.0.0.0 0.0.0.0 0.0.0.0 1 so-0/0/1.0 PtToPt 0.0.0.0 0.0.0.0 0.0.0.0 1 so-0/0/2.0 PtToPt 0.0.0.0 0.0.0.0 0.0.0.0 1 so-0/0/3.0 PtToPt 0.0.0.0 0.0.0.0 0.0.0.0 1 user@R6> show ospf interface Interface State Area DR ID BDR ID Nbrs so-0/0/0.0 PtToPt 0.0.0.0 0.0.0.0 0.0.0.0 1 so-0/0/1.0 PtToPt 0.0.0.0 0.0.0.0 0.0.0.0 1 so-0/0/2.0 PtToPt 0.0.0.0 0.0.0.0 0.0.0.0 1 so-0/0/3.0 PtToPt 0.0.0.0 0.0.0.0 0.0.0.0 1
Sample Output 2
user@R1> show ospf interface Interface State Area DR ID BDR ID Nbrs lo0.0 DR 0.0.0.0 10.0.0.1 0.0.0.0 0 so-0/0/0.0 PtToPt 0.0.0.0 0.0.0.0 0.0.0.0 1 so-0/0/1.0 PtToPt 0.0.0.0 0.0.0.0 0.0.0.0 1 so-0/0/2.0 PtToPt 0.0.0.0 0.0.0.0 0.0.0.0 1 user@R3> show ospf interface Interface State Area DR ID BDR ID Nbrs lo0.0 DR 0.0.0.0 10.0.0.3 0.0.0.0 0 so-0/0/0.0 Down 0.0.0.0 0.0.0.0 0.0.0.0 0 so-0/0/1.0 PtToPt 0.0.0.0 0.0.0.0 0.0.0.0 1 so-0/0/2.0 PtToPt 0.0.0.0 0.0.0.0 0.0.0.0 1 so-0/0/3.0 PtToPt 0.0.0.0 0.0.0.0 0.0.0.0 1 user@R6> show ospf interface Interface State Area DR ID BDR ID Nbrs lo0.0 DR 0.0.0.0 10.0.0.6 0.0.0.0 0 so-0/0/0.0 PtToPt 0.0.0.0 0.0.0.0 0.0.0.0 1 so-0/0/1.0 Down 0.0.0.0 0.0.0.0 0.0.0.0 0 so-0/0/2.0 PtToPt 0.0.0.0 0.0.0.0 0.0.0.0 1 so-0/0/3.0 PtToPt 0.0.0.0 0.0.0.0 0.0.0.0 1
Meaning
Sample Output 1 shows that all interfaces on all routers are in the correct area (0.0.0.0), and the loopback (lo0) interface is missing from the list of interfaces on all routers. The missing loopback (lo0) interface is a problem in this configuration.
In an MPLS network configured with OSPF as the IGP, when you manually configure the RID, it is important to explicitly configure the loopback interface at the [edit protocols ospf] hierarchy level. If the RID is not manually configured, OSPF automatically advertises the loopback (lo0) interface. In the configuration of all the routers in this network, the RID is configured manually, therefore, the loopback (lo0) interface must be explicitly configured at the [edit protocols ospf] hierarchy level. In addition, the loopback (lo0) interface is configured with the passive statement to ensure that the protocols are not run over the loopback (lo0) interface and it is correctly advertised throughout the network.
Sample Output 2 shows that all the relevant interfaces on the ingress, transit, and egress routers, including the loopback (lo0) interface, are in the correct area (0.0.0.0). Because the configuration of the interfaces is correct, further investigation is required to determine the reason for the LSP problem.
