We have a Ubuntu 14.04 server which is running Plesk 12.5. I have an issue where SSH connections appear to get blocked, and I can't figure out why.
If we do a dozen connections over a short time period (less than a minute) (all with correct details, login and work fine) then they start to be refused. It appears to be limited to the ip address since I can ssh in fine from a different location.
This happens with different users of the system, and once that ip has hit the limit (if that is what it is) no user on that same ip can login.
When it's blocked, I have checked IPTables, and there is no entry in there. I have grepped the whole of /var/log/ for the ip, and nothing found there either.
Where on earth could it be getting limited?
Edit Fail2Ban is on the server, but nothing in the logs (or IPTables), and all the the connections are with correct details, so shouldn't trigger an error.
This is on a VPS, I would doubt there is a firewall in front of it.