Disable SSH password authentication
Any system administrator that checks the system logs often will find that the most common of things when it comes to ssh is brute-forcing.
To fix this issue permanently we must disable password authentication.
You do this by firs setting up login by certificate. Copy the contents of your ~/.ssh/id_rsa.pub into the ~/.ssh/authorized_keys file on the server, or run ssh-copy-id [server IP address]
After that open /etc/ssh/sshd_config, find the line that says #PasswordAuthentication yes, and change it to PasswordAuthentication no.
Restart the SSH server daemon to apply the change
sudo service ssh restart
Now, the only possible way to SSH into the server is to use a key that matches a line in ~/.ssh/authorized_keys. Using this method, brute force attacks drop because even if they guess any password, it will be rejected.
Brute-forcing a public/private key pair is impossible with today's technology.