Firewall

A hardware device or software program that monitors and filters incoming and outgoing network traffic depending on rules.

Features

• traffic type detection
• source & destination address-port logging
• usage of an ACL
• packet filtering (based on destination or type of data contained in the packet)
• transmission protocol filtering (deny or allow TCP/UDP connections) - called circuit-layer gateways
• pseudoproxy => all outgoing packets allowed by the firewall look like they're from the firewall itself
• stateful inspection (session layer) => peek into the packet content when session starts, keep relevant information. if it passes firewall settings, let it through for the rest of the session freely, else DIE