Firewall Technologies

A firewall is a concept that can be implemented by a single device, a group of devices, or even simply software running on a device such as a host or a server. As mentioned in the introduction to this chapter, the function of a firewall primarily is to deny unwanted traffic from crossing the boundary of the firewall. For network traffic, this means that a firewall, in its basic form, could be implemented by the following:

Image A router or other Layer 3 forwarding device that has an access list or some other method used to filter traffic that is trying to go between two of its interfaces. This is the primary method that is implemented ...

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