Mastering Linux Security and Hardening

Hands-on lab for basic iptables usage

You'll do this lab on your Ubuntu virtual machine.

1. Shut down your Ubuntu virtual machine, and create a snapshot. 

You'll roll back to this snapshot for the lab in the next section.

2. Look at your iptables rules, or lack thereof, with:

        sudo iptables -L

3. Create the rules that you need for a basic firewall, allowing for Secure Shell access but denying everything else:

        sudo iptables -A INPUT -m conntrack                                       --ctstate ESTABLISHED,RELATED                      -j ACCEPT        sudo iptables -A INPUT -p tcp --dport ssh -j ACCEPT        sudo iptables -A INPUT -j DROP

4. View the results with:

        sudo iptables -L

5. Oops, it looks like you forgot about that loopback interface. Add a rule for it at the top of the list:

 sudo iptables -I INPUT 1 -i ...