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, 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.

Software Routers

If you have more PCs than money, you might choose to use one of them as a software router or, as it is sometimes also called, a proxy server. If you use a PC in this way, it must stay on for as long as you want to use any of the others. It is generally slower than hardware routers.

Remember that all your clients should have their own firewall and virus protection software installed. Usually, the host computer that runs routing software will have two network cards: one for the DSL/cable modem and the other for your local area network (LAN). You can buy several software packages for this job:

• Wingate
• Sygate

For Macs:

• IPNetRouter
• SurfDoubler

Prices for the others can range from $35 to $700, depending on the number of users and other add-ons, such as parental controls. But you may already have a software router.

Windows 98SE and Windows 2000/XP include Internet Connection Sharing (ICS) as a bundled function. If your PC does not already have it, you can’t download it from the Microsoft web page, although those pages are a good source of advice and software updates.

ICS provides for sharing a single Internet connection to a small peer-to-peer network such as with Wi- Fi’s ad hoc mode. ICS requires a host computer as a Dynamic Host Configuration Protocol (DHCP) Server that dynamically hands out IP addresses to as many as 10 other network PCs as they boot up and ask for them.

It also includes the functions of a domain name server (DNS) proxy. When one of your clients refers to a web site by its alphabetic name, the Internet must first translate it to an IP address, as you might do with a telephone directory.

These requests must be shuttled back and forth through the server PC along with other traffic. The ICS server also uses application programming interfaces (APIs) to aid configuration, report status, and manage the dial-up. (Yes, you can use it with a telephone modem if you must.)

Hardware Connection Sharing

One of the killer applications for home Wi-Fi is sharing connections to a broadband Internet link. To do this, you will have to set up your wireless workstations in infrastructure mode. This means that in order to communicate to each other, they will all first go through a wireless hub.

This connects them to each other, and the built-in router will in turn connect them all to your cable or DSL modem. Thanks to a hungry mass market and economies of scale, the cost of hardware routers has dropped, often to a price lower than software-based equivalents. These intelligent devices do everything that the software routers can do.

What’s more, modern hardware routers usually have other functions built in that otherwise would require you to make several purchases and to integrate several pieces of hardware afterwards. Most Wi-Fi routers usually include four or more RJ-45 sockets to accept and interconnect traffic from your wired PCs or your existing LAN hubs.

These ports are switched, meaning that traffic is selectively channeled between them so that any one port sees only the data destined for it. The older hubs acted like a party line, with heavy traffic on one echoed onto all, thus sapping their capacity.

The built-in switched ports auto-sense speeds of 10 or 100 Mbps and interface between computers or networks running at different speeds. Some routers include ports for printers, enabling you to share one printer among several home-office PCs, wired or otherwise.

Some have built-in telephone modems that will dial and share a connection to your ISP when the DSL line fails. Home routers come in different flavors, some having specialized built-in interfaces that connect directly to existing “no new wires” media, such as phone- or power-line home networks.

It is possible to combine interfaces, thereby adding a Wi-Fi cell to a phone-line network that includes a shared Internet link. For this task, you will need an access point, which is a simplified version of a Wi-Fi router. Access points have only one wired port. Their purpose is to provide a pathway from a Wi-Fi cell, making it appear as a wired PC to a preexisting wired network.