The procedure for opening ports in the Linux firewall "iptables" is relatively simple.
First, open a command-line terminal. In most systems, you can usually find this in your 'Applications' menu under the 'System Tools' section.
Once you have a terminal open, you have to obtain root access to change firewall settings. Do this by typing:
You will be prompted for your root password.
In the following examples, substitute the port # you want to open for the 12345 in the command.
If you want to open an incoming TCP port, type the following:
iptables -I INPUT -p tcp --dport 12345 --syn -j ACCEPT
If you want to open a UDP port (perhaps for DHT in Tixati), type the following:
iptables -I INPUT -p udp --dport 12345 -j ACCEPT
After you are done opening ports in your firewall, you can save your changes so they will be applied when you restart your computer by typing the following command:
If you also have a broadband NAT router for your internet connection and want to configure it to forward incoming TCP connections or UDP packets, read the Forwarding Ports In A Broadband Router