Functions of Packet Filtering

Packet filtering is often integrated into routers or bridges to restrict the flow of information. Packet filters allow administrators to control protocol-specific packets so that they can only be delivered locally on the network; to quarantine email domains; and to perform other packet transmission control functions.

Packet filters are an important feature used in firewalls, which examine the headers of IP packets to determine the packet's source address, destination address, and the network transport service utilized by the packet. Traditional packet filters are static, allowing or denying packets to pass based only on the contents of the packet header and a combination of rules. Intrusion detection systems utilize packet filtering techniques and analyze packets by matching them to pre-defined characteristics, and then warn of possible network hackers and intruders.

Packet filters are also a key tool in network sniffing, protocol analyzers, or packet analyzers. Many network sniffing tools have multiple filter types, thus enabling users to filter packets and see how they are transmitted.