Network Security Hacks, 2nd Edition

Chapter 4. Firewalling

When designing a network, it’s often desirable to define policies governing how and where certain vital network services can be accessed. The firewall is a key technology that is instrumental in enforcing these policies and can allow network administrators to delineate trust relationships between networks and hosts with a fine grain of detail.

By instituting a firewall, you can prevent unauthorized access to services at the network level before an attacker is given the chance to attempt to exploit them. You can use a firewall not only to limit what information flows into a network, but also to prevent the egress of information. Doing so aids in preventing worm propagation and helps stop important confidential information from leaving an enterprise. Additionally, firewall logs can be excellent tools to help you understand where the threats to your network originate.

A variety of firewalls are available today. In addition to the many firewall appliances that are available, Linux, BSD, and Windows all include some form of firewalling support. This chapter shows how to set up firewalls with Linux, FreeBSD, OpenBSD, and Windows, as well as how to test your firewall rulesets. You’ll also see how to perform MAC address filtering and how to create a gateway that will authenticate machines based on login credentials. Finally, you’ll learn a few additional tricks to keep certain types of traffic from exiting your network.

Firewall with Netfilter

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