Opening and closing ports in Linux…

I have recently shifted to Ubuntu 24/7, when I am not in office and was setting it up for Bittorrent to work. Linux is awesome because it’s closed most of the time. Consequently to set up and run Bittorrent files, you need to have the torrent ports – [6881-6999] open.

So, what do you do to make sure that they are open when you require them to be and closed when you don’t want them to be. Of course, you don’t need to open all the ports as well.

You need to go to IPTABLES and give this particular command

sudo iptables -A INPUT -p tcp --dport 6881 -j ACCEPT

This means – Append a line for the option INPUT, for the protocol [-p] tc for the destination port [--dport] 6881. Accept the packet that is coming from there.

And to close the port -

sudo iptables -A INPUT -p tcp --dport 6881 -j DROP

Now, if you wanna download a couple of torrent files, you need to keep at least 5-10 ports open as torrent clients check for the ports 6881-6999 in the increasing order.

I typically keep 6881-6999 open when I wanna download torrents.

So, that would mean typing the aforementioned code 10 times and to close the ports when not needed [i.e.] another 10 times.

Here in comes the beauty of shell script and attached here – are 2 shell scripts that I use to open and close the ports when I wanna download the torrents and then block them!

Accept_Torrent_Ports

# Shell script to accept Torrent Ports from 6881 to 6889
# Author: Guru Panguji
# Date: 03-June-2007
clear
echo "Will open Torrent Ports from 6881-6889"
echo "Use ./Drop_Torrent_Ports to close the Ports"
sudo iptables -A INPUT -p tcp --dport 6881 -j ACCEPT
sudo iptables -A INPUT -p tcp --dport 6882 -j ACCEPT
sudo iptables -A INPUT -p tcp --dport 6883 -j ACCEPT
sudo iptables -A INPUT -p tcp --dport 6884 -j ACCEPT
sudo iptables -A INPUT -p tcp --dport 6885 -j ACCEPT
sudo iptables -A INPUT -p tcp --dport 6886 -j ACCEPT
sudo iptables -A INPUT -p tcp --dport 6887 -j ACCEPT
sudo iptables -A INPUT -p tcp --dport 6888 -j ACCEPT
sudo iptables -A INPUT -p tcp --dport 6889 -j ACCEPT

Drop Torrent Ports

# Shell script to accept Torrent Ports from 6881 to 6889
# Author: Guru Panguji
# Date: 03-June-2007
#
clear
echo "Will close Torrent Ports from 6881-6889"
echo "Use ./Accept_Torrent_Ports to open the Ports"
sudo iptables -A INPUT -p tcp --dport 6881 -j DROP
sudo iptables -A INPUT -p tcp --dport 6882 -j DROP
sudo iptables -A INPUT -p tcp --dport 6883 -j DROP
sudo iptables -A INPUT -p tcp --dport 6884 -j DROP
sudo iptables -A INPUT -p tcp --dport 6885 -j DROP
sudo iptables -A INPUT -p tcp --dport 6886 -j DROP
sudo iptables -A INPUT -p tcp --dport 6887 -j DROP
sudo iptables -A INPUT -p tcp --dport 6888 -j DROP
sudo iptables -A INPUT -p tcp --dport 6889 -j DROP