The OpenBSD packet filter, PF, is central to the OpenBSD and FreeBSD network toolbox. With more and more services placing high demands on bandwidth and an increasingly hostile Internet environment, no sysadmin can afford to be without PF expertise. The fourth edition of The Book of PF covers the most up-to-date developments in PF, including new content on IPv6, dual stack configurations, the 'queues and priorities' traffic-shaping system, NAT and redirection, wireless networking, spam fighting, failover provisioning, logging, and more. You'll also learn how to: Create rule sets for all kinds of network traffic, IPv4 and IPv6 both, whether crossing a simple LAN, hiding behind NAT, traversing DMZs, or spanning bridges or wider networks. Set up wireless networks with access points, and lock them down using authpf and special access restrictions. Maximize flexibility and service availability via CARP, relayd, and redirection. Build adaptive firewalls to proactively defend against attackers and spammers. Harness OpenBSD's latest traffic-shaping system to keep your network responsive, or use ALTQ and Dummynet configurations on FreeBSD to full effect. Stay in control of your traffic with monitoring and visualization tools (including NetFlow). The Book of PF is the essential guide to building a secure network with PF. With a little effort and this book, you'll be well prepared to unlock PF's full potential. Covers OpenBSD 7.6 and FreeBSD 14.x.