From Wikitech

Runbook for 'SSH unreachable' alerts

  1. Try logging in via the mgmt interface. Can you get a console from there? What is the output?
  2. sshd can be overwhelmed by rapid attempts to connect; if you can get on the host and things seem normal, check /var/log/auth.log for errors
  3. If you can get on the host, run 'ip link show' to check if there is physical network connection
  4. If 3) fails, escalate the issue to the dcops team.