Understanding Firewalls

Chapter 3 introduced firewalls when describing differences between the Internet, an intranet, an extranet, and a demilitarized zone (DMZ). Firewalls filter the traffic that is allowed into or out of a network. They can be dedicated physical devices primarily filtering traffic, and they can also be software running on a system such as a desktop computer.

Basic packet filtering firewalls filter the traffic by examining each individual packet. More advanced firewalls filter the traffic by examining the overall session or actual protocol commands embedded in the packets. Additionally, firewalls can be network-based, providing protection for an entire network of systems, or host-based, providing protection for a single operating ...

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