Packet Filtering Rules

A packet filter firewall is configured with a set of rules that define when to accept a packet or deny. When the firewall receives a packet, the filter checks the rules defined against IP address, port number, protocol, and so on. In particular, if a rule says 'accept,' then the packet is accepted in the network, otherwise it is dropped (= the packet isn't sent to the destination.)

The following table contains an example set of rules that tell a firewall what do to with packets: