• Telnet, SSH and other access to the router was not working.
• Also “show log messages” commands were getting stuck.
• Ping to the lo0 IP of the router was dropping from time to time.

Step-1: Check the SSH configuration. If not there then enable ssh under [system services]

set system services ssh 

Step-2: Check the SSH connection-limit if any. If we are hitting the limit, then increase the limit.

set system services ssh connection-limit 15

set system services ssh rate-limit 60

Step-3: Check for any config changes from customer side. If the issue has been observed after config changes, then revert the changes to confirm if the config changes caused the issue.

Step-4: In this case, the issue occurred after the config changes. Checking the config changes it was found that there was ISIS-BGP-VXLAN-GRE on the same link. Suspected the issue could be with MTU as there were so many overheads involved. The root cause of the issue has been found to be the MTU size issue. After MTU issue has been addressed, the ssh and other started working fine.