Fail2Ban is a tool used on web servers for protecting unauthorised access through bruit force attempts.
This works by allowing a small amount of login attempts before it drops the remote IP into the iptables and blocking them untill fail2ban unblocks. Occasionally this can catch out genuine login attempts.
To Unblock an IP
1. Check the IP Tables for the IP
iptables -L -n
2. Check Active Jails
3. Unban using Fail2Ban
fail2ban-client set JAIL unbanip IPADDRESS
fail2ban-client set ssh unbanip 184.108.40.206