Figure 14-7 Firewall
The primary function of all firewalls is to screen network
traffic and prevent unauthorized access between two
network entities. There are several types of firewalls:
Packet filtering firewalls: Individual packets are examined,
although the firewall does not know the contents of a packet. These
firewalls provide this security by filtering the packets of incoming traffic
and distinguishing between TCP/UDP traffic and port numbers. The
packets are either allowed entry onto the network or denied access,
based on either their source or destination address or some other static
information, such as the traffic type. Figure 14-8 shows an example of a
stateless firewall that has a very simple rules engine and shows which
traffic is allowed and which is denied.