SSH: short for Secure Shell, SSH (developed by SSH Communications Security Ltd.) is a secure protocol for remote logins. Using an SSH client, a user can connect to a server to transfer information in a more secure manner than other methods, such as telnet. Below is an example of how an SSH session, which uses a command line interface, may look. SSH defaults to port 22.
Modify the SSH remote login port to 9999
Add a port to the firewall
The default iptables only open port 22 for ssh service, the use of additional ports such as 9999 need to add this port to a white list in iptables. If you don’t add this port, you will not connect to the SSH server.
You need to save the command to the iptables configuration file