Case Study Troubleshooting Neighbor Problems

When you execute a show ip ospf neighbor command and it reveals nothing or it shows nothing about the particular neighbor you are analyzing, it indicates that this router has seen no valid OSPF Hellos from that neighbor. Check the following items:

1 Is the local router or neighboring router's interface up, with line protocol up? Use the show interface command to find out.

2 Check for IP connectivity between the neighboring routers as follows: A Can you ping the neighbor?

B Does the neighbor respond if you ping 224.0.0.5? (This is the address to which OSPF Hellos are sent.)

C Check for any inbound access lists or other devices (such as a switch) that might prohibit sending/receipt of IP packets from one neighbor to the other.

3 Is OSPF enabled on the interfaces in question (that is, your router's interface and the neighboring router's interface)? Use the show ip ospf interface command to determine if OSPF is enabled.

4 Is OSPF configured as passive for the local router's or neighboring router's interface? (Use the show running-config command to check the configuration.)

150 Chapter 3: OSPF Communication

— Verify that the following Hello parameters match on the neighboring interfaces of both routers:

— Same OSPF area (use the show ip ospf interface command to determine).

— Same type of OSPF area, such as stub or NSSA (use the show ip ospf command to check).

— Same subnet and subnet mask (use the show interface command to check).

— Same OSPF Hello and dead timer values (use the show ip ospf interface command to check).

TIP OSPF adjacencies are formed only over primary networks and not secondary networks.

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