Firewalls are a network response to a software engineering problem.

—Steve Bellovin

Firewalls are a key part of any security infrastructure. Once viewed as a choke point at the very front end of a network, they are now liberally sprinkled around enterprises allowing for security administrators to enforce fine-grained access control to any asset. They are viewed as an enabling technology assisting businesses and individuals in performing activities in a secure and reliable fashion.

FreeBSD and OpenBSD make great platforms for firewall deployments. Through their stable development process, the BSDs can be configured in a very secure fashion. This is key, as a firewall is the nexus for many network-borne attacks and an insecure firewall makes for an insecure network. Further, the BSDs provide high performance networking that is fundamental to the scalability of a firewall. Firewalls can control access to many different networks at once, so it is critically important for a firewall to maintain low latency even under heavy load.

This chapter discusses configuration, deployment, and administration of FreeBSD and OpenBSD-based firewalls. It compares and contrasts the features available under each operating system as well as provides example configurations for common firewall scenarios. Finally, this chapter provides a solution for high availability architectures with these open source solutions.