- Freecom Router User Manual

Network Address Translation

When you visit a website via your computer, your router, or more specifically

your NAT, remembers which computer on the internal network asked for the

information. When the information (in this case the website you asked for)

comes back, the router knows which computer on the internal network to send

the information to. This is Network Address Translation or NAT.

Developed by Cisco, Network Address Translation is used by a device (firewall,

router or computer) that sits between an internal network and the rest of the

world. For more information about IP address translation, refer to RFC 1631, The

IP Network Address Translator (NAT).

Hosting a server

What If I want to host a server?

For others to be able to view your pictures on your computer, you need to run

some type of service or server. A web server such as apache will allow others to

securely watch the pictures or files on your site. But how does the NAT of your

router know this time to which computer to forward the information?

Since the request comes from the internet, most routers are setup to disallow any

traffic going into the internal network. (Firewall protection) In this case, since we

want people to be able to see our pictures, we want the router to forward this

information. We have to tell the router to do this.

Someone calling from the internet asks your router for a certain "port". This is

the same as someone calling the receptionist and requesting a certain person by

name. Ports are displayed as numbers but invariably map to pre described

services. For instance, when someone requests a web page, they always ask for

the service on port 80, the web server. Through NAT, it is possible to "map" a

certain request for a service (a request for a port) to a certain PC on the internal

network.

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