This one comes in very handy at times.
Log onto the server and
su – to become root.
To see what IPs are blocked type the following:
iptables -L -n
This will output the iptables list and at the bottom you will see the Chain fail2ban-SSH
Chain fail2ban-SSH (1 references) target prot opt source destination RETURN all -- 0.0.0.0/0 0.0.0.0/0
To remove the customer's IP from the block list type the following:
iptables -D fail2ban-SSH -s IP -j DROP
Switch the IP with the customer's public IP address.
This will remove the user from the block list and they should be able to access the dedicated server.