I have a router modem and no firewall.
If the firewall on your router is not active, than you will have to open port 22 (sshd) using the above mentioned command.
But first take a look at your iptables rules. It may already be open.
To do that, open a terminal window (console... command line).
To create, modify or remove rules, you have to be root.
Type the following command and enter the root password:
To view your iptables rules, type: