Definition and purpose
iptables is a traditional Linux utility for managing IPv4 packet-filtering rules through the Netfilter subsystem.
Technical operation
Rules are evaluated in chains such as INPUT, OUTPUT and FORWARD, in tables including filter and nat. Depending on the distribution, the iptables command may use an nftables compatibility backend or legacy infrastructure.
Practical example
An administrator can restrict service access to a trusted subnet, permit established connections and reject other traffic. Rule ordering matters because packets follow the configured chain logic.
Operational considerations
Check which backend is active, persist rules appropriately, account for IPv6 separately and maintain out-of-band recovery access when editing remote firewall policies.