AAM6030BI User Manual
6.
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 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 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
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 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 computer 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
router. The 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
What is a CPE?
The Internet is so large that a single network cannot handle all of the traffic and still deliver a reasonable
level of service. To overcome this limitation, the network is broken down into smaller segments or subnets
that can deliver good performance for the stations attached to that segment. This segmentation solves the
problem of supporting a large number of stations, but introduces the problem of getting traffic from one
subnet to another.
To accomplish this, devices called routers or CPEs are placed between segments. If a machine wishes to
contact another device on the same segment, it transmits to that station directly using a simple discovery
technique. If the target station does not exist on the same segment as the source station, then the source
actually has no idea how to get to the target.
One of the configuration parameters transmitted to each network device is its default CPE. This address is
configured by the network administrators and it informs each personal computer or other network device
where to send data if the target station does not reside on the same subnet as the source. If your machine
can reach all stations on the same subnet (usually a building or a sector within a building), but cannot
communicate outside of this area, it is usually because of an incorrectly configured default CPE.
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