Appendix b: adsl router terms, What is a firewall, What is nat – NetComm NB5 User Manual
Page 20: What is a dmz
NB5 Quick Start Guide
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 func tion ality 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
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