Lab 17: Linux Firewall Exploration

Lab Overview

The learning objective of this lab is for students to gain insights on how firewalls work by playing with firewall software and implement a simplified packet filtering firewall. Firewalls have several types; in this lab, we focus on two types, the packet filter, and application firewall.

Packet filters act by inspecting the packets; if a packet matches the packet filter's set of rules, the packet filter will either drop the packet or forward it, depending on what the rules say. Packet filters are usually stateless; they filter each packet based only on the information contained in that packet, without paying attention to whether a packet is part of an existing stream of traffic. Packet filters often use a combination of the packet's source and destination address, its protocol, and, for TCP and UDP traffic, port numbers.

The application firewall works at the application layer. A widely used application firewall is web proxy, which is primarily used for egress filtering of web traffic. In this lab, students will play with both types of firewalls, and also through the implementation of some of the key functionalities, they can understand how firewalls work.

Lab Description

Please find the lab description here.

Handin

Please write your lab report according to the description. Please also list the important code snippets followed by your explanation. You will not receive credit if you simply attach code without any explanation. Upload your answers as a PDF to blackboard.

Suggested Reading

• SEED Book Chapter 17
• A Mini-Firewall Program (the code has been tested on SEEDUbuntu 16.04 VM)
• Creating a simple "hello world" Netfilter module
• Creating a Netfilter kernel module which filters UDP packets
• Parsing program options using getopt
  

Acknowledgements

Most content taken from Wenliang Du.

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