Terminology
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What is a Firewall?
A firewall is protection between the Internet and your local network. It acts as the firewall in your car does, protecting the interior of the car from the engine. Your car's firewall has very small opening that allow desired connections from the engine into the cabin (gas pedal connection, etc), but if something happens to your engine, you are protected.
The firewall in the router is very similar. Only the connections that you allow are passed through the firewall. These connections normally originate from the local network, such as users web browsing, checking
What is NAT?
NAT stands for Network Address Translation. Another name for it is Connection Sharing. What does this mean? Your ISP provides you with a single network address to access the Internet with. However, you may have several machines on your local network that want to access the Internet at the same time. The router provides NAT functionality that converts your local network addresses to the single network address provided by your ISP. It keeps track of all these connections and makes sure that the correct information gets to the correct local machine.
Occasionally, there are certain programs that don't work well through NAT. Some games and other specialty applications have a bit of trouble. The router contains special functionality to handle the vast majority of these troublesome programs and games. NAT does cause problems when you want to run a server. See the DMZ section below.
What is a DMZ?
DMZ really stands for Demilitarized Zone. It is a way of separating part of your local network so that is more open to the Internet. Suppose that you want to run a web server, or a game server. Normal servers like these are blocked from working by the NAT functionality. The solution is to isolate the single local computer into a DMZ. This makes the single computer look like it is directly on the Internet, and others can access this machine.
January 2005 |