How to protect against attacks like brute force on your beautiful dedicated.

In this configuration, flange port 12345 which has been changed to SSH. we drop all frames except for some IP.
for approval on several IP address
sudo iptables-A INPUT-i eth1-p tcp-dport 12345-s 10.10.210.210-j ACCEPT
sudo iptables-A INPUT-i eth1-p tcp-dport 12345-s 10.10.2.120-j ACCEPT
sudo iptables-A INPUT-i eth1-p tcp-dport 12345-j DROP

Save definitely Iptables configuration and load at startup:

S

With that you are safe for SSH, be careful not to cut your legs.