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Cable Modems

Networking and Broadband

With broadband Internet connections becoming more common daily, and home networking also on the increase, the same question keeps popping up in discussion groups - I've got a cable modem and a network, how do I connect all my computers to the Internet?

There are several possible answers, each with its own advantages and disadvantages. But first, the problem. With broadband connection you are allocated an IP address, which gets associated with your cable modem and your network interface card (NIC). The NIC has a MAC address which is stored by the ISP as an accepted PC (i.e. it knows who is allowed to access the system, who has paid their connection fee). Many ISPs only allow you to have two registered MAC addresses.

If you try to connect your home network to the cable modem via a hub, the cable modem sees all the MAC addresses of the computers on the network and gets confused. It thinks it should only be seeing one, and you can't get Internet access. This is true of all modems, not just cable modems.

The 56K Modem Solution

If you run some special software, you can fool a 56K modem into only seeing one computer. Windows includes an Internet sharing package, called Microsoft Internet Connection Sharing, or ICS for short. This works by making one of the computers a gateway, your primary connection to the Internet, and the networked computers talk to the Internet through this computer, which must always be on when the rest of the network wishes to go on-line.

Normally what you do is set up the gateway computer independently to access the Internet via your ISP. Then install and connect up you home network, normally via a hub if you have more than two computers, or via a crossover cable if you only have two. Set up the network to communicate using TCP/IP protocol (same protocol as the Internet uses). Then you run the ICS wizard to enable sharing. To do this go to Start, Control Panel, Add/Remove Programs, Windows Setup tab, Internet Tools, and check Internet Connection Sharing and OK. Then follow the on-screen instructions, and everything works fine

The Cable Modem Problem

But it's not as easy with a cable modem as when using one of the older 56K modems. Because the cable modem connects to the Internet via an NIC. There are various ways round this.

If you only have two computers with NICs, you can register each one's MAC seperately with the broadband ISP. Then you have to go through a silly proceedure to swap computers every time you wish to put the other one on to the Internet. You have to discard the current allocated IP using winipcfg (Start, Run, winipcfg, click on More, and then Release). Then disconnect the current computer, connect the other one, boot up. and wait for the cable modem to realise that you've swapped things over and acquire a new temporary IP connection for you. This can take quite some time the first time you do it - they say allow several hours for it to work! Not exactly practical, is it?

So the recommended ways are as follows: -

Solution One

Set up your primary computer as the one connected to the Internet. Install a second NIC in this computer, and use this NIC to make you home network connection. Then run the ICS wizard. This works well, if the primary computer is connected directly to the cable modem via its first NIC (the normal way to use broadband). It will not work through a hub connected to the cable modem, but you can use a hub to network the computers themselves. This is ideal for occasional connection of, say, a laptop to the Internet, or two computers in the same room.

The big disadvantage to some people is that the primary computer, the gateway, must be on before any of the others can go on the Internet. If you only want to connect your laptop occasionally, this isn't a big deal. But if you have a home network with several computers in different rooms, typically one for each of the kids and one for the adults, then there are continual calls of "Are you online", "Don't switch off yet!", "Who pulled the plug on the gateway?!" And if the gateway computer is locked in a room, switched off, and the room owner isn't around, no-one gets online. The bigger your home network, the more of a problem it becomes, and you should then consider the next solution.

Solution Two

The alternative is to use a router, such as the Netwear R114 at about £80, instead of a hub. This is just a bit over the top for a two-computer network where a simple crossover cable would network the two machines. But for three or more computers, you will be going out to buy a hub anyway to wire up the network. Okay, the price has just trebled compared to a basic hub, but there are advantages.

The router can be used as a firewall to keep out unwanted intruders - you do have a firewall of some sort for your broadband connection, don't you? There is no need for a gateway computer to be switched on first to make the Internet connection. Your home network will run a bit faster as traffic will be directed to the correct computer, not broadcast over the entire network.

Solution Three

If you have a USB port, some cable modems can be connected directly to the gateway computer using this port, and then the network computers connected to each other via the NIC. This has the same problems as the first method, in that the gateway has to be on for the others to access the Internet. However, like solution one, it is very cheap, very simple and handy for occasional connections or simple two-computer networks. The gateway ccomputer will run a little bit slower, as it now has to do some of the processing that was done by the NIC.

Solution Four

A final alternative, suitable for those who only occassionally want to connect a second computer to the Internet, is if you have a USB port on each computer, and an NIC in the main one. There are special cables that allow you to connect two computers together making a small, slow network via the USB ports, You MUST use the correct type of cable to do this, as the USB port on each computer sends out a power supply to make the USB port drive some devices, the cable has the same plug on each end (A to A connectors), and of course the equivalent of a crossover connection is made as well. This is NOT a data transfer cable, the commonest, cheapest USB connecting cable. The EZ-Link USB connector is the sort of cable you need. These cables have a small electronic device in the middle which does all the clever technical stuff to make it work. This is most suitable for a laptop connected to the main computer to upgrade the laptop's software perhaps. As a network, it is a bit slow (1 Mb compared to the typical 100 Mb NIC).

One thing you must not try with a USB cable is try to connect several computers to a USB hub and the cable modem. It's not that sort of hub, it's designed so that one computer can talk to several periferal devices (scanner, printer, digital camera and so on).

Cable Modem Links

The Cable Modem Centre

Rod's SURFboard Pages

HowStuffWorks - Cable Modems

Cable Modem Help

Speed Guide

Cable Modems Dropping Offline

Cable Modem Troubleshooting Tips