Networking 101 - TvTechnology

Networking 101

Brad Gilmer answers a reader's question about his Computer Networking for Beginners article in this month's Reader Feedback column.
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Networking 101

Hello Brad,

I've just finished reading your January article, “Computer Networking for Beginners — Part 1,” and I have a couple of questions.

First, take the company who is assigned an IP address by the ISP. Why would anyone choose a subnet mask other than 255.255.255.0?

What would be the purpose of choosing, for example, 255.255.255.252, which allows only two IP addresses?

Second, my company uses NetBEUI protocol on its NT4.0 network and, as far as I know, TCP/IP is not installed. Does every device on the network still have an IP address?

Also, a related issue that you haven't discussed so far in your series is how to handle firewalls on a network. Does the firewall need to be installed on every computer on the network or only the one that serves as the gateway to the Internet? (We have DSL through one computer, which is then distributed over the LAN with an Alcatel router.)
Art Wagner

Brad Gilmer responds:

Hi Art,

First, thanks for your interest in the article. Now on to your questions: First, regarding subnets, almost everyone I know uses a subnet of 255.255.255.0. This is easy to remember and makes sure that all addresses on the network are usable. However, you might consider using a different subnet if for some reason you wanted to set a limit on the number of computer addresses on the network. This might be desirable if, for instance, you were setting up a network to be used only by a set number of computers in, say, the accounting department, and didn't want someone else to come in and grab another address on this network.

Perhaps others would disagree, but I would say keep it simple and use 255.255.255.0 unless you have a specific reason to limit the address range on your network.

On your second question, NetBEUI and TCP/IP can co-exist, but they are separate networking technologies. In the old days, NetBEUI/NetBIOS comprised Windows Networking. But as TCP/IP became the dominant networking technology, Microsoft modified NetBIOS to run on top of TCP/IP. This greatly reduced the everyday usage of NetBEUI in medium- to large-scale networks. If you enable TCP/IP on your network, each computer will need its own IP address, but you can run NetBEUI by itself. If you do that, all you need is to assign each computer to a workgroup (usually Workgroup), and assign each computer a computer name. If you would like to run NetBEUI alongside TCP/IP, you can do that too. All you need to do is enable TCP/IP in the “Properties” of the particular network card you are using. If you want to replace NetBEUI with TCP/IP, you can do this and still run NetBIOS. So it all depends on how you would like to configure your network.

On your firewall question, whether or not you need to install a firewall on every computer on the network depends on how the gateway is configured. If the gateway is configured to do network address translation (NAT) to conceal the addresses of computers on your internal network, and if the gateway is running a firewall to block things like the ports that enable Windows for Workgroups, then you only need one firewall. If the gateway is not running a firewall, then I strongly recommend running a firewall on each computer. Also, if some of the computers in your company are laptops, they should be running firewalls in case their owners dial into the Internet while traveling. People have their own preferences, but I have been very happy with the Zone Alarm firewall. If you want to check to see if your computer is exposed, you can go to www.grc.com and run the tests under the “Shields Up!” section of the site. This great site run by Steve Gibson provides a quick test to see how vulnerable your computer is to hacking over the Internet.

To Brad Gilmer:

Well… you've done it again!

You've said in two short pages what an entire networking for dummies book took two chapters to do.

Good article and good job!

Best,
Tony

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