In Cisco switches, when there is an OSPF Router ID Conflict and routers have duplicate Router IDs in the OSPF domain, you may receive the following type of log message:

%OSPF-5-ADJCHG: Process <Process_ID>, Nbr <Neighbor_IP>, Loopback interface is down, OSPF Neighbor down: Dead timer expired

Explanation of the log message:

  • %OSPF-5-ADJCHG: This log message indicates an OSPF adjacency change.
  • Process <Process_ID>: The log message includes the OSPF process ID for the specific OSPF instance running on the Cisco switch.
  • Nbr <Neighbor_IP>: This part shows the IP address of the OSPF neighbor with whom the adjacency has changed.
  • Loopback interface is down: This section indicates that the OSPF adjacency issue is related to the loopback interface being down.
  • OSPF Neighbor down: Dead timer expired: The last part of the log message highlights that the OSPF neighbor adjacency has gone down due to the expiration of the dead timer, indicating a possible Router ID conflict.

The log message serves as a notification to network administrators that a Router ID Conflict may be causing OSPF neighbor adjacency problems. Duplicate Router IDs in the OSPF domain can lead to neighbor adjacency issues and disrupt OSPF routing operations. Network administrators should promptly address the Router ID Conflict to ensure the stability and proper functioning of OSPF in the network.

Solution:

Open Shortest Path First (OSPF) is a widely used dynamic routing protocol that plays a crucial role in efficient data exchange and routing decisions within a network. However, when routers in the OSPF domain have duplicate Router IDs, it can lead to neighbor adjacency problems, disrupt OSPF routing, and impact network performance. Resolving OSPF Router ID Conflict is vital to ensure stable neighbor adjacencies and the smooth functioning of OSPF. In this article, we will explore the common challenges related to OSPF Router ID Conflict and provide a step-by-step solution using proper commands to address and resolve this issue on Cisco devices.

Understanding OSPF Router ID Conflict: The OSPF Router ID is a unique identifier assigned to each router in the OSPF domain. The Router ID serves as an important parameter in OSPF operations, and duplicate Router IDs can cause severe neighbor adjacency problems. OSPF Router ID Conflict may arise due to misconfigurations, duplicate loopback addresses, or conflicting OSPF process ID configurations.

Solution for Resolving OSPF Router ID Conflict:

Step 1: Verify OSPF Router IDs: Check the OSPF Router IDs of all routers in the OSPF domain to identify any duplicates. Use the following command on each router:

show ip ospf

Step 2: Identify the Duplicate Router IDs: Identify the routers with duplicate Router IDs from the output of the previous command. Make a note of the conflicting Router IDs and the corresponding router interfaces.

Step 3: Modify the Router IDs: Change the Router IDs of the routers with duplicate IDs to unique values. You can modify the OSPF Router ID using one of the following methods:

Method 1: Using the Router ID Configuration Command:

router ospf <Process_ID>
router-id <New_Router_ID>

Replace <Process_ID> with the OSPF process ID and <New_Router_ID> with the new unique Router ID for the router.

 

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