In the last post I walked you through a script to create a stateful packet inspection firewall. Which allowed out-going traffic to the internet, but which blocked in-coming traffic. In this part I’m going to explain how to open up specific ports (or holes). To allow certain types of internet traffic successfully through.

As with the earlier articles, there are a few basic parts that rules can be filtered for. These four parts are as follows:

- IP Addresses: a single address (94.76.240.128), or multiple addresses in a range (94.76.240.128-150)

- Interface: eth1,ppp0,wlan0 (these are usually names of physical network ports on your computer)

- Ports: a single port (http 80) or a range of ports

- Protocols: icmp, tcp, udp, all

(Continue Reading…)

Welcome back to this the second part of the discussion about IPtables, if you missed the first part you can find it here. As mentioned previously, I plan to get into some basic usage and hands-on practice. A few notes before we get started. Firstly: IPtables from the CLI requires root or administrative access for the majority of commands. Second: for these demonstrations, we will be erasing all current existing entries.

I highly recommend that these be practiced on a home machine where you have admin rights and aren’t using IPtables as your active firewall. Since deleting the configuration will leave the computer vulnerable to attack. Under no circumstances should this be practiced on a live production network (i.e at work). Myself nor GBServers will be held responsible for any possible damages by ignoring these suggestions. I’d go as far as suggesting: unplugging your computer from the internet. You can practice with computers on your home network. You don’t necessarily need to be connected to the internet.

Also be aware that while Linux distros are more or less the same. There can be some differences in how services are started such as IPtables. But if you have read the first article, you hopefully have gotten IPtables installed as well as learned how to turn it on and off. With that said, lets get started..

(Continue Reading…)