Paradyne 6218 A

6218-A2-GB20-00 February 2005 A-1

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 e-mail, downloading files, and

playing games. However, you can allow incoming connections so that you can run

programs like a web server.

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 sever al machines o n

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.

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.