Packet Filtering Routers are a type of firewalls that are invented first. These are designed with a main aim of filtering the IP packets, and this filtering is done based on four fields and they are given below:

  • TCP source port/ UDP source port
  • TCP destination port/ UDP destination port
  • Source IP address
  • Destination IP address

The IP packets are filtered by these firewalls for the following reasons:

  • To block connections to certain ports
  • To block connections to certain hosts or certain networks
  • To block connections from certain ports
  • To block connection from certain hosts or certain networks.

                    Generally all the ports or the hosts can be specified while the routers are configuring in specific situations. The performance of the packet filtering routers will be fast because the content in the IP packets is not inspected before it is dropped or forwarded that means there port fields are also not checked before transferring the content. For the IP packets these packet filtering routers are the guards who may ask certain questions like “who are you”, “where are you going” etc. In this case the guard of a building allows a person enter in to the build when once he answered all his questions and in similar way these firewalls will also behave.