> How many linux books got out of date covering linux firewalling? what is the firewall cli/rules language du jour at the moment? There's one for every finger o

> How many linux books got out of date covering linux firewalling? what is the firewall cli/rules language du jour at the moment? There's one for every finger on my hand... I'd argue that it's iptables, and has been for the last 20 years. In Linux 1.1 (1994) there was a port of FreeBSD's ipfw. ipfw was replaced by ipchains in Linux 2.2 (1999). However, ipchains was quickly replaced by iptables in Linux 2.4 (2001). And now since Linux 3.13 (2014) iptables is slowly being replaced by nftables, but most of its use is the iptables userland being ported to use the nftables kernel interface; the nftables native userland (`nft`) only just hit 1.0.0 this month. Other higher level "more user friendly" wrappers have come and gone; Ubuntu's ufw (which wraps iptables), RedHat's firewalld (which wraps nftables), and uh one for each finger of my hand. But at the end of the day, they're iptables/nftables under the hood, and when you want to configure things they way you would with pf, you skip those layers and go straight for iptables.