Packet filter firewall

A packet filter firewall is a routing device that include access control functionality for system addresses and communication sessions. The access control functionality of a packet filter firewall is governed by a set of rules that allows or blocks network packets based on a number of their characteristics, including the source and destination addresses, the network protocol, and the source and destination port numbers.

Packet filter firewalls are usually placed at the outermost boundary with an untrusted network, and they form the first line of defense. An example of a packet filter firewall is a network router that employs filter rules to screen network traffic.