Firewall

A firewall is a security barrier between a trusted network (like your server) and an untrusted one (like the internet). It examines every incoming and outgoing network connection and decides whether to allow or block it based on a set of rules. Firewalls can be software running on your server (iptables, ufw, Windows Firewall), hardware appliances, or cloud-based services (Cloudflare WAF, AWS Security Groups). A properly configured firewall is your first line of defense against unauthorized access.