A Guide to Networking an NTL Cable Modem Service

One of the MFAQs (Most Frequently Asked Questions) seen on Cable Modem or Broadband Newsgroups is "How do I share my Cable Modem?"

This site hopefully answers this particular question for users of the NTL Cable Network service although certain portions of the information held here could apply to other ISP Cable Modem Services and ADSL.

Whoever your ISP happens to be and whether you are networking a Cable Modem or ADSL connection, or even a dial-up connection, there remains only a couple of ways of actually providing Internet services to machines on your network through your Internet Connection:

1. Via a PC acting as a Network Router or Gateway, or;

2. Via a device that is designed to be a Network Router or Gateway.

Both of these alternatives are very easy to define but the options available to implement either solution make the whole process of networking seem extremely complicated. While it seems that way, in reality, connecting any network to any other network is really quite a simple affair. All it requires is a basic understanding of the way the networks operate and then the application of the necessary tools to allow the networks to communicate. This applies to either public or private networks and also applies to your own network when connected to your Cable Modem, and thence to the Internet.

Before the discussion turns to the Cable Modem sharing options it is worth just making a couple of definitions clear. In networking terms a router and a gateway have two distinctly different functions, but the usage of the terms tends to get muddled when describing the operation of devices used to connect one network to another:

Definition of a router: A router is a network device that takes data from one network in order to deliver it to it's destination network.

Definition of a gateway: a gateway is a network device that provides connectivity from one network to one or more other networks.

For the purposes of the following pages I have used these definitions to mean the same thing as it is very easy to confuse the two. It is not helped by the fact that most Un*xes have their default designated as a router, and Microsoft call theirs a gateway. In a network purists' view, the first is correct - we are defining our default TCP/IP router, but the machine is also our gateway to other networks, so in that case, the second is correct. However, in most cases, I tend to follow the following rules; 1) a PC acting as a router is a gateway, and 2) A router is a router, never a gateway;-)

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