Which of the following can be thought of as the simplest and almost cheapest type of firewall?

A.
stateful firewall

B.
hardware firewall

C.
PIX firewall

D.
packet filter

E.
None of the choices.

Explanation:

The simplest and almost cheapest type of firewall is a packet filter that stops messages with
inappropriate network addresses. It usually consists of a screening router and a set of rules that
accept or reject a message based on information in the message header.