State about the Packet filter firewalls

They remain the most common type of firewall in use as of today. They were the earliest firewalls developed and were capable of permitting or denying traffic based on certain simple field-level filters which could determine such things as source or destination packet address, or the protocol being used. The greatest advantage is that they are fast since they have minimum processor overheads, and are transparent as well as inexpensive. On the downside, they are not strong enough at the application level. This is because these firewalls work purely at the level of network layer, making them difficult to configure and manage effectively.

Most of the present day routers include capabilities of such firewalls as a standard feature in their system. This kind of packet filtering can be found in almost every major firewall available today.