Network Security, Firewalls, and VPNs, 3rd Edition

Types of Filtering

Filtering is the primary function of a firewall, and most devices can support many different forms of filtering. Through its filtering services, most of the other benefits and capabilities of firewalls apply. Additionally, the terms for the type of filtering and the type of firewall are often used interchangeably. For example, a firewall that supports packet filtering is known as a packet-filtering firewall.

Static Packet Filtering

The most common form of filtering is static packet filtering. Static packet filtering uses a static or fixed set of rules to filter network traffic. The rules can focus on source or destination IP address, source or destination port number, IP header protocol field value, ICMP types, fragmentation ...