ADSL and network configuration

As a greater number of entry-level ADSL (Asymmetric Digital Subscriber Line) modems start to provide affordable router functionality, there is no doubt they will become a popular upgrade for users who want to get the most from their ADSL connection. This guide will show you how you can utilise these modems’ built-in routers to set up a local area network (LAN) and, in turn, distribute your broadband connection across multiple computers.The top down:

  • Specify settings. You may decide to let the ADSL modem handle the LAN functions via its DHCP (Dynamic Host Configuration Protocol) server, but if you want to specify individual settings for all the PCs in your network we will show you how to disable the server to do this. This will give you more flexibility if you wish to use advanced features such as port forwarding.

    A DHCP server is the mechanism that automatically distributes IP addresses, and other network information, as soon as it detects a PC on the network. This IP address will change every time the PC is rebooted, and in this type of setup your network cards must also be configured to obtain network addresses automatically.

    A static IP address is one which never changes. All the computers on your network will require these if the DHCP server is to be disabled.

  • LAN configuration. An Internet connection can be shared only once a LAN has been properly configured. As noted, for a PC to be recognised on the network it must have a unique IP address. This is usually in the range of to, although it will depend on your modem’s settings. Refer to your modem manual for specific information.

    In addition, for each computer to access the Internet, each one must have a gateway address as well as a DNS (Domain Name Server) address. Put simply, without a gateway address, the PC will not know where to go to access the Internet, and without a DNS address it will not be able to translate the words you type in the address bar of your Web browser into numerical IP addresses.

    These settings can be entered into your PCs manually by accessing the Control Panel as seen here. In Windows 9x, click Start-Settings-Control Panel-Network and then double-click TCP-IP. You can specify an IP address from this screen, and you will also need to enter a subnet address. All PCs in the network must be on the same subnet and the standard address of will suffice. Next, click the Gateway tab. In this space you will need to enter the IP address of your ADSL modem, which will be your gateway to the Internet. This number can be found in the product manual, and it is the same address that you use to access the Web configuration utility of your modem. Make sure you click Add and then the DNS Configuration tab. Enable the DNS setting and, once again, enter the modem’s IP address as the DNS server, and ensure that you click Add. Click Apply, then OK and restart your computer when prompted.

    In Windows XP, all these settings can be entered from one screen and without restarting. To do so, go to the Control Panel and double-click Network Connections. Right-click on your network adapter and select Properties. Then click Internet Protocol (TCP/IP) and enter the IP, Subnet, Gateway and DNS settings as required.

  • ADSL modem configuration. Once each PC has been configured with its own IP address and all DNS and gateway settings have been added, launch your Web browser and enter the IP address of your modem into the address bar. Enter your login details when prompted and navigate to the section of the interface where the DHCP server settings reside. Disable the DHCP server and save the changes. This picture illustrates this procedure using the Billion BIPAC 5100A modem.

  • Ensure all PCs can access the modem. The next step is to ensure that all the PCs in your network can access the modem. This can be done by launching a DOS prompt in Windows 9x, or a Command prompt in Windows XP, and then pinging the address of your modem, as seen here. If you receive a reply, then your computer is successfully seeing your modem. Try pinging the other machines in your network, too.

    Finally, enter your ISP user-name and pass-word into the modem to enable your ADSL con-nection. When a con-nection to your ISP has been established, you will be able to access the Internet over any computer in your network.

The top down:

Benefits: Shared broadband connection

Cost: $100-$450

Level of expertise: Intermediate

Time required: Less than an hour

Tools required: None

Vendors: Refer to Best Buys in May 2004 print edition

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Elias Plastiras
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