iptables is a utility which I was fairly familiar with around the time it was displacing ipchains but have tended to deal with it rarely since that time. It is now apparently also deprecated in favor of nftables, but end-of-life'ing will likely take a bit of time.

Given that I don't deal with firewall related concerns directly too often (though I do have some related projects in the wings), iptables is primarily relevant to me within the context of containerized execution environments and routing across the resulting network namespaces, and a larger scale handling some intra-cluster routing within environments such as kubernetes.