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Setting Up an ADSL Router for your network

An ADSL router will enable all the machines on the network to use the internet connection through a single access point. This could mean mail to the desktops, user browsing or making the network available via VPN (Virtual Private Networking). Whatever the reasons, using a router to connect to the internet is cheaper and more efficient than multiple access lines.

Getting Started with Routers

First of all, you need to run TCP/IP on your network. You can check this by clicking network properties on your PC and should see something like this:

or if you have a Mac (don't let people get you down about this), you should see this in the control panel:

All your computers should then terminate via Cat5 cable to a hub. Sometimes there may be a patch panel in the middle, but that is not our concern.

Plugging the Router into the Hub

Next we need to plug the router into the hub. The hub should have an uplink slot in it which allows several hubs to be daisy-chained together. We need to use that port to uplink to the router. If you don't have an uplink port available, don't worry you can use a cross over cable which can be bought from any PC shop - even PC World.

This is the back of a Vigor 2600X router/hub:

As you can see, there are plenty of slots, but just pick one of the LAN slots to connect to the network. The ADSL slot plugs into the wall outlet for your ADSL line. That's it ! - Well almost.

There is an amount of configuration required which will not be discussed in detail here. This document is concerned with an overview of the network and how it works.

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The ADSL Network Overview

How it all works

The router acts as a gateway between the internal network which will be addressed in the 192.168.?.? range. But we know from previous pages that there are many instances of that IP range in the world so the router masks the internal network from the internet.

IP Addressing for the ADSL Router

The router is able to perform its function by having 2 IP addresses. One is within the range of the internal network such as 192.168.1.1 and the other is a public IP address which sites on the outside of the router. When a user on the network makes a TCP/IP request that cannot be resolved on the local network, it the uses the gateway which then resolves the request at a public dns server and the request gets passed to resource on the internet. The internet resource then passes the information back to the public IP address on the outside of the router.

How does the Router know which computer to send the request back to?

Each network card has a MAC address - nothing to do with apples, its an enormously long number which is unique to that card. When the request is passed to the router, the router makes a note of the MAC address of the requestee's computer and stores it in a register until the response is received by the router. The router then checks the MAC address in the register and sends the data to the device in question.

Who Chooses the External IP for the Router?

The external IP of your router is allocated by your ISP. This will either be the same IP number each time - we call this a fixed IP or it will be allocated from a pool of available IP numbers which the ISP has available. Because of the different billing structure of ADSL, the chances that you will have the same IP (even if you do not subscribe to the fixed IP service) are much higher than with traditional dial in services.

Finding the IP Number of your Router

If you are using one of Gconnect's ADSL Routers you can enter the gateway number into your ADSL Router and use the control panel. The external IP number is listed under the WAN heading or the status heading.

For more information on specific routers please look at the ADSL Routers and ADSL Modems page here.

Links

http://www.scit.wlv.ac.uk/~jphb/comms/iproute.html