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Chapter 3. Sharing a Connection > Choosing a Configuration

Choosing a Configuration

There are several ways to configure your network to share a broadband Internet connection. Which configuration you choose is dependant on how much work you want to take on, what kind of connections you want for each PC, and the type of service offered by your broadband ISP.

The Bridge Configuration

The most common type of network configuration for sharing an Internet connection is called a bridge. In this configuration, the broadband connection is routed first to the broadband modem, and then to your network hub. Each PC on your network is also connected to the hub, and assigned a separate IP address by your ISP. A bridge connection is illustrated in Figure 3.2.

Figure 3.2. A bridge configuration for sharing an Internet connection.


Some broadband ISPs provide multiple IP addresses as part of their basic service; others charge extra for additional addresses. Still others won’t provide additional IP addresses at all. (If this latter description fits your ISP, you’ll have to choose a different type of configuration.)

The chief advantage of the bridge configuration is that it’s easy to set up and configure. It’s dependent, however, on your ISP providing additional IP addresses, which could add a few dollars onto your monthly ISP bill.

PPPoE Sharing

If you’re stuck with a PPPoE broadband connection (see Chapter 2, “Making the Broadband Connection,” for details), you’ll use a modified version of the bridge configuration. In this variation, the connections are all as described; the difference is that you’ll need to install PPPoE software on your PCs.

With a shared PPPoE connection, none of your PCs are assigned permanent IP addresses. Instead, the PPPoE software assigns a temporary IP address to each computer each time it logs on to the Internet.

The Combination Modem/Hub Bridge Configuration

If you have a DSL connection, some DSL modems also function as network hubs. To use a DSL modem/hub to connect multiple PCs, you create a modified bridge configuration. The broadband connection is routed directly to the modem/hub, and then each PC is connected to the modem/hub. This type of configuration is illustrated in Figure 3.3.

Figure 3.3. A bridge configuration using a combination modem/hub.

Using a modem/hub is a nice option, if offered by your DSL supplier. It’s probably the easiest configuration possible, and it eliminates the need to purchase and install a separate network hub.

The Gateway Configuration

This configuration uses a lead computer as a “gateway” to the Internet. This gateway computer is the only computer on your network that is visible to the Internet, and it manages the connections for all the other PCs.

Part of this connection management involves the assignment of private IP addresses and name resolution services for all the other computers on your network. When one of the other PCs on your network accesses the Internet, that computer’s private IP address is transmitted to the gateway computer; the gateway computer translates the private IP address to its own address, and sends the information out to the Internet. Translation back to the initiating PC is made when information is downloaded from the Internet to the gateway PC.

As you can see in Figure 3.4, you set up a gateway configuration by routing the broadband connection first to the broadband modem, and then to the gateway PC. The gateway PC then connects to your network hub; all your other PCs are also connected to the hub.

Figure 3.4. In the gateway configuration, a lead computer serves as a gateway to the Internet for all your other PCs.


For a gateway configuration to work, the gateway computer has to have two network cards installed—one connected to the modem, and one connected to the network hub.

To manage a gateway configuration, special Network Address Translation (NAT) software has to be installed on your lead computer. If you have a recent version of Windows, you have that software already built into your operating system. (See “Using Internet Connection Sharing,” next.) If you have an older version of Windows or a non-Windows operating system, you’ll need to install a third-party NAT program, such as Sygate Home Network (www.sygate.com) or NAT32 (www.nat32.com) .


Before you attempt to set up a gateway configuration, check with your ISP to make sure that your broadband modem is NAT-compatible.

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