Using Firewall Linux has a tool called iptables, which is essentially a firewall. It has a nice front end program called ufw, which provides easy user interface. In this task, the objective is to use ufw to set up some firewall policies, and observe the behaviors of your system after the policies become effective. You need to set up at least two VMs, one called Machine A, and other called Machine B. Please check Appendix A in the manual for how to set up two VMs. You run the firewall on your Machine A. Basically, we use ufw as a personal firewall. Optionally, if you have more VMs, you can set up a firewall at your router, so it can protect a network, instead of just one single computer. After you set up the two VMs, you should perform the following tasks:
• Prevent A from doing telnet to Machine B.
• Prevent B from doing telnet to Machine A.
Before starting the task, go to the default policy file /etc/default/ufw. find the following entry, and change the rule from DROP to ACCEPT; otherwise, all the incoming traffic will be dropped by default. # Set the default input policy to ACCEPT, DROP, or REJECT. Please note that if # you change this you will most likely want to adjust your rules. DEFAULT_INPUT