Firewall
A network security system that monitors and controls incoming and outgoing traffic based on defined rules.
A firewall in Linux is a network security system that monitors and filters incoming and outgoing network traffic based on a set of predefined rules. It acts as a barrier between a trusted internal network and untrusted external networks such as the internet. The Linux kernel includes a built-in firewall framework called Netfilter, which is configured through user-space tools. The traditional tool is iptables, which provides fine-grained control over packet filtering, network address translation (NAT), and port forwarding. Modern Linux distributions have moved toward nftables as the successor to iptables, offering improved performance and a cleaner syntax. Many distributions also provide simplified frontend tools such as UFW (Uncomplicated Firewall) on Ubuntu and firewalld on Fedora and RHEL. Properly configuring a firewall is essential for securing Linux servers and workstations, controlling which services are accessible from the network, and preventing unauthorized access.