How old is that article? (not that it's bad but it feels a bit old)

It references very old Linux kernels, Slackware 10 (released in 2004), old hardware with little RAM, it talks about iptables (it still exists and the syntax is fine, but it's just now mostly an abstraction/compatibility layer on top of nftables) and there's no mention of IPv6 (if I'm not mistaken on most stacks now DNS queries are made for both IPv4 and IPv6).