Appendix B Adsl Router terms, What is a firewall?

Appendix B: ADSL Router terms

What is a firewall?

A ﬁrewall is protection between the Internet and your local network. It acts similarly to the ﬁrewall in your car, 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 ADSL Router is very similar. Only the desired connections that you allow are passed through the ﬁrewall. These connections are normally originating from the local network; such as web browsing, checking your email, downloading a ﬁle, and playing a game. However, in some cases, you can allow incoming connections so that you can run programs like a web server.

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 for you to access the Internet through. However, you may have several machines on your local network that want to access the Internet at the same time. The ADSL 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 some applications have a bit of trouble. The ADSL 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 though. When running a server, please see the DMZ section below.

What is a DMZ?

DMZ really stands for Demilitarized Zone. It is a way of separating out 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 com- puter look like it is directly on the Internet, and others can access this machine.

Your machine isn’t really directly connected to the Internet, and it really has an internal local network address. When you provide the servers network address to others, you must provide the address of the ADSL Router. The ADSL Router “fakes” the connection to your machine.

You should use the DMZ when you want to run a server that others will access from the Internet. Internal programs and servers (like print servers, etc) should NOT be connected to the DMZ

NB5 Quick Start Guide	YML763Rev220
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