A packet filter is a type of a firewall that examines network traffic based on the informaion recorded in the packet headers and performs some action with that traffic. Usually a packet filter would be installed on a router that separates a LAN from the internet or other untrusted network. A packet filter can also be installed on a personal workstation. Most packet filters that I know have the following elements:

  • a language allowing to describe traffic patterns
  • a set of actions (deny, accept, drop, log) to be performed on identified traffic

Some well known packet filters are Berkeley Packet Filter and Netfilter