Sharing a Broadband Internet Connection

Raymond J. Smith, WiFi Home Networking, McGrawHill Companies


If you have an existing network, and you’ve just installed a broadband link to the Internet, you can make that link work for all your existing computers, whether the link is via satellite, cable modem, or Telco digital subscriber line (DSL). You should check with your Internet service provider (ISP) before you do so, however, because their policies vary. Most don’t mind customers sharing access among their own PCs. Most do mind customers sharing with friends or neighbors. Some don’t care, and some flatly forbid it and actively seek out users who share in any way. As mentioned in the previous chapter, you should base your choice of ISP on this policy question as well as on other factors.

The simplest way to share an Internet line is to purchase additional Internet Protocol (IP) addresses from your ISP. No providers complain about this method, because they make a profit on the exchange. Prices may vary from $3 to $10 per month, assuming that your ISP is willing or able to sell extras.You will need one for each PC you plan to connect. Afterward, all the PCs will have to be interconnected through a hub or switch, which will also have a line to your broadband modem.

It is possible to achieve the same end by using a clever device that selectively channels traffic between the broadband link and your client PCs. It is called a router. This function can be carried out by a dedicated PC running special software or by a piece of special-purpose hardware. Many hardware routers are made more cost effective by including built-in firewalls
and high-speed switches, which makes them an increasingly popular solution for broadband sharing. Software and hardware routers are Network Address Translation (NAT) devices. They emulate a single PC when they connect to your ISP. They will even perform an auto-logon if they have to. Afterward, any traffic destined for a PC in your home is directed (routed) to it as though it were the only PC, even though you may have several. Similarly, any traffic from any PC to the Internet gets funneled into one DSL line. This provides an extra measure of security for your PCs because to someone on the outside it appears as though only one IP address is active. In this way, a NAT router acts as a firewall.

Another measure of security is gained from the range of IP addresses distributed to the clients, because they belong to a special class:
- 10.0.0.0 to 10.255.255.255
- 172.16.0.0 to 172.31.255.255
- 192.168.0.0 to 192.168.255.255 (the most common)

Addresses in this range function like any others, with the exception that Internet routers won’t pass them along. This means that your PCs are more isolated and therefore more protected. A hacker trying to access any of your addresses within these limits will have no luck, as his or her packets will hit an immediate dead end. DSL and cable are full-time Internet connections.

They make your PCs easier to find and more vulnerable to attacks from malevolent hackers than they were on your old dial-up connection. This is especially true if you have a static IP address since a hacker can automatically “bookmark” your home network and return to it at leisure.


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