Firewalls provide administrative control over Internet Protocol (IP)-level communications amongst network-connected computers. That communication is leveraging either Transmission Control Protocol (TCP) or User Datagram Protocol (UDP).
Firewall software (or hardware) provides a way to manage the IP ports and type of traffic (TCP/UDP) that is permitted to pass through these ports. Entry-level firewalls, such as the one provided with Windows, provide nonstateful packet inspection. To put it simply, they can provide either blocked or unblocked access from network-based computers, based upon their source address or network (scope setting) to the machine that is being configured.
Stateful packet inspection firewalls provide for tracking ...