We have already introduced the concept of firewalls in Chapter 1, Differentiating between Internets, Intranets, and Extranets. Recall that a firewall can either block or deny network traffic based upon certain criteria. In this section, we will look at the common forms of firewall.
Firewalls
Packet-filtering firewalls
Packet-filtering firewalls are the most basic of firewalls. They are able to block or allow network traffic based on source or destination IP address, ports, or protocols within the header of the traffic. Because only the header is inspected and no analysis of the actual payload of the network traffic is carried out, this is quite a fast process. The downside to this is that it is not very secure, as traffic...
