In Cisco switches, when there is an OSPF Authentication Key Mismatch and OSPF routers have different authentication keys configured, you may receive the following type of log message:

%OSPF-5-ADJCHG: Process <Process_ID>, Nbr <Neighbor_IP> on <Interface> from FULL to DOWN, OSPF Authentication Key Mismatch

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.
  • on <Interface>: The log message specifies the name of the interface where the OSPF adjacency change occurred.
  • from FULL to DOWN: This section indicates that the OSPF adjacency transitioned from the FULL state (active adjacency) to the DOWN state (inactive adjacency).
  • OSPF Authentication Key Mismatch: The last part of the log message highlights that the issue is related to different OSPF authentication keys being configured, causing the adjacency problem.

The log message serves as a notification to network administrators that an OSPF Authentication Key Mismatch may be preventing OSPF routers from forming neighbor adjacencies. Incorrect or mismatched authentication keys can lead to failed authentication between OSPF routers, disrupting OSPF routing operations and impacting network connectivity. Network administrators should address the OSPF Authentication Key Mismatch to ensure proper authentication key configurations and stable OSPF routing within the network.


when OSPF routers have different authentication keys configured, an OSPF Authentication Key Mismatch occurs, leading to the inability to form neighbor adjacencies. This can result in disrupted OSPF routing operations and compromised network security. In this article, we will explore the challenges of OSPF Authentication Key Mismatch and provide a step-by-step solution using commands to resolve the issue on Cisco devices, ensuring secure neighbor adjacencies.

Understanding OSPF Authentication Key Mismatch: Authentication keys are used in OSPF to ensure secure communication between OSPF routers. When OSPF routers have different authentication keys configured on the same interface, the authentication process fails, and neighbor adjacencies cannot be established.

Solution for Resolving OSPF Authentication Key Mismatch:

Step 1: Verify OSPF Authentication Keys: Check the configured authentication keys on each OSPF router within the network. Use the following command on each router:

show running-config | include authentication-key

Step 2: Identify the Mismatched Keys: Identify the routers with mismatched authentication keys from the output of the previous command. Make a note of the conflicting keys and the corresponding router interfaces.

Step 3: Synchronize Authentication Keys: Choose a common authentication key that will be shared among all OSPF routers within the network. Use the following command on each router to synchronize the authentication keys:

interface <Interface>
ip ospf authentication-key <Common_Key>

Replace <Interface> with the name of the OSPF interface, and <Common_Key> with the desired authentication key.

Step 4: Clear OSPF Process: Clear the OSPF process on each router to apply the changes and ensure synchronization of authentication keys:

clear ip ospf process

Conclusion: Resolving OSPF Authentication Key Mismatch is essential for secure and efficient neighbor adjacencies within the network. By following the step-by-step solution provided in this article and using the correct commands on Cisco devices, network administrators can quickly identify and rectify authentication key discrepancies. Establishing a common authentication key ensures successful authentication between OSPF routers, promoting secure communication and stable OSPF routing operations. Regular monitoring and proactive management of OSPF authentication key configurations will contribute to a robust and well-protected OSPF network infrastructure, ensuring optimal network performance and data security.

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