In Cisco routers, when a BGP authentication mismatch occurs, you might encounter log messages that provide information about the authentication failure. These messages can help you diagnose and address the issue. Here’s an example of a log message you might see in this scenario:

% BGP-3-NOTIFICATION: received from <neighbor-IP> 2/6 (authentication failure) 0 bytes

Explanation of the log message components:

  • % BGP-3-NOTIFICATION: This part indicates that the log message is related to BGP and specifically a BGP notification message.
  • received from <neighbor-IP>: This portion specifies the IP address of the BGP neighbor from which the notification was received.
  • 2/6 (authentication failure): Here, 2 represents the BGP notification code for an authentication failure, and 6 is the subcode that provides additional details about the type of failure.
  • 0 bytes: This part indicates the length of the data associated with the notification message. In the case of an authentication failure, the length might be minimal or zero.

In the log message example provided, the notification code 2 and subcode 6 specifically point to an authentication failure. This log message suggests that the BGP session between the local router and the specified neighbor failed due to authentication mismatch.

To troubleshoot this issue, you would need to review the BGP configuration on both routers, ensuring that the authentication keys, algorithms, and passwords match. Additionally, comparing the logs and configurations of both routers can help pinpoint the exact cause of the authentication failure and guide you in resolving the mismatch.

Troubleshooting steps:

BGP (Border Gateway Protocol) is a critical protocol used for routing between autonomous systems. Ensuring secure communication between BGP neighbors is essential for maintaining network integrity. Authentication mismatch is a common issue that can disrupt BGP peering. In this article, we will guide you through troubleshooting and resolving BGP authentication mismatch on Cisco routers using relevant commands.

Step 1: Identifying the Issue:

  1. Check the router logs for authentication-related errors:

show logging | include BGP-3-NOTIFICATION

Step 2: Verify BGP Configuration:

  1. Verify authentication settings for the BGP neighbor:

show run | section router bgp

Step 3: Verify BGP Peering State:

  1. Check the BGP status and peering state:

show ip bgp summary

Step 4: Resolve Authentication Mismatch:

  1. Ensure both routers use the same authentication algorithm and password:
    • Go to BGP configuration mode:

router bgp <AS-number>

Configure the authentication settings:

neighbor <neighbor-IP> password <password>
neighbor <neighbor-IP> password <password> md5

2.Clear the BGP session to apply changes:

clear ip bgp <neighbor-IP>

3.Monitor the BGP session re-establishment:

show ip bgp summary

Conclusion: BGP authentication mismatch can disrupt network connectivity and compromise security. By following the troubleshooting steps outlined in this article and using the provided Cisco commands, you can identify, resolve, and prevent authentication mismatch issues on Cisco routers. Remember that maintaining consistent authentication settings and monitoring BGP peering status are crucial for ensuring a stable and secure BGP network