What aspects should I diagnose? CSF disabled via csf -x doesn't help. I can only connect to this server via our backup server on BackupSy which I luckily setup password less ssh via Public Key Authentication . Other machine I tried to access via SSH doesn't work and all timeouts. Website/Forums on that server works fine. I can also access the main IP via browser/port 80. Even if I manually added my desktop public key on the server, still can't connect, maybe because I'm not yet registered as known host?