What is Iptables?

Iptables controls network traffic by processing packets through chains of rules in the filter, nat, mangle, and raw tables. The filter table (INPUT, FORWARD, OUTPUT chains) handles packet filtering. The nat table manages Network Address Translation for routing. Rules specify match criteria (source/destination IP, port, protocol) and targets (ACCEPT, DROP, REJECT, LOG). Iptables processes rules sequentially — the first matching rule wins. While being replaced by nftables on modern systems, iptables remains widely used and is the foundation for Docker networking and Kubernetes kube-proxy. The ip6tables variant handles IPv6 traffic.