Two QFX5100s were having issues with TACACS authentication. Logs show they were unable to connect to the TACSCS server. Server was known to be working as other switches are able to connect to it. This issue arose after a storm-related power outage.

From the logs messages only seeing tacplus failing on sending the authentication:

Aug 16 22:27:03.235 2024 switch-name sshd: %USER-TEST_TACPLUS_SEND_AUTHEN_FAIL: Failed in sending authentication with error connect: timed out.Aug 16 22:59:52.398 2024 switch-name  sshd: %USER-TEST_TACPLUS_SEND_AUTHEN_FAIL: Failed in sending authentication with error connect: timed out.
Aug 16 23:00:19.934 2024 switch-name  sshd: %USER-TEST_TACPLUS_SEND_AUTHEN_FAIL: Failed in sending authentication with error connect: timed out.

A simple reboot of the affected QFX5100 switches resolved the TACACS authentication issue. The reboot process allowed the system to recover from any corruption and re-establish normal operations.

To mitigate the risk of future issues caused by power outages, consider implementing the following preventive measures:
 

• Uninterruptible Power Supply (UPS): Connect the switches to a UPS to provide a buffer of power during brief outages.

This can reduce the likelihood of system corruption and improve the overall reliability of your network infrastructure.