Asus AAM6030BI Manuel de l'utilisateur - Page 38

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AAM6030BI User Manual

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.