Packet Filter Devices

Currently, it is rare for a packet filter to be a stand-alone device. Most packet filtering occurs as an extra function on routers. A router is a special purpose computer dedicated to determining the correct place a packet should be sent and then forwarding it to the next appropriate network or computer along the way toward its final destination.

Most routers come with extra software built-in which allows them to filter packets. The router is programmed (configured) by the end user as to which addresses and services it should filter.

The filtering usually occurs in the network card of the router. This allows for the fastest filtering. The filtering can also occur within the operating system of the router, instead of in the network card, but it is slower.

Sometimes regular computers such as PCs, are also used as packet filtering devices. When they are used, filtering occurs in the operating system of the computer. This type of packet filter device is rare today, because it is slower and because a router is already required to connect a network to the Internet, with or without a firewall.