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Chapter 20. A Network Security Primer > Understanding Firewalls

Understanding Firewalls

Firewalls are designed to sit between your network and the Internet and protect the internal network from outside attack. A firewall will examine data leaving and entering the internal network and can actually filter the data traveling in both directions. If data packets do not meet a particular rule that has been configured, the data is not allowed to enter the internal network or leave the internal network. This means that firewalls not only protect a network from outside attack, but they can also control the type of connections made by users on the internal network to the outside (meaning that employees can be restricted from connecting to certain Web sites).

Firewalls are typically a combination of hardware and software, and they really don’t look that much different from other connectivity hardware, such as hubs and routers. Firewalls are manufactured by a number of companies, including Cisco, 3Com, and Ascend Communications. Firewalls come in a variety of models that have been designed to protect different size networks. For example, 3Com manufactures the OfficeConnect firewall line as a security tool for small companies. For larger enterprise networks, 3Com offers the SuperStack 3 firewall. The SuperStack 3 firewall is designed to control large numbers of VPN connections (we discuss VPN, or Virtual Private Networking, in Chapter 17). This firewall also provides support for IPSec.


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