6.4. Firewalls

Contributed by Gary Palmer <gpalmer@FreeBSD.org> .
4th of October 1995

Firewalls are an area of increasing interest for people who are connected to the Internet, and are even finding applications on private networks to provide enhanced security. This section will hopefully explain what firewalls are, how to use them, and how to use the facilities provided in the FreeBSD kernel to impliment them.

Note: People often think that having a firewall between your companies internal network and the ``Big Bad Internet'' will solve all your security problems. It may help, but a poorly setup firewall system is more of a security risk than not having one at all. A firewall can only add another layer of security to your systems, but they will not be able to stop a really determined hacker from penetrating your internal network. If you let internal security lapse because you believe your firewall to be impenetrable, you have just made the hackers job that bit easier.

6.4.1. What is a firewall?

6.4.1.1. Packet filtering routers

6.4.1.2. Proxy servers

6.4.2. What does IPFW allow me to do?

6.4.3. Enabling IPFW on FreeBSD

6.4.4. Configuring IPFW

6.4.4.1. Altering the IPFW rules

6.4.4.2. Listing/flushing the IPFW rules

6.4.5. Example commands for ipfw

6.4.6. Building a packet filtering firewall