ipfirewall - Wikipedia
https://en.wikipedia.org/wiki/Ipfirewall
ipfirewall or ipfw is a FreeBSD IP, stateful firewall, packet filter and traffic accounting facility. Its ruleset logic is similar to many other packet filters except IPFilter. ipfw is authored and maintained by FreeBSD volunteer staff members.
IPFW
http://www.servaris.com/docs/handbook/firewalls-ipfw.html
The IPFW stateless rule syntax is empowered with technically sophisticated selection capabilities which far surpasses the knowledge level of the customary firewall installer.
29.4. Ipfw
https://www.linuxsecrets.com/freebsd-handbook/firewalls-ipfw.html
IPFW is a stateful firewall written for FreeBSD which supports both IPv4 and IPv6. It is comprised of several components: the kernel firewall filter rule processor and its integrated packet accounting...