http://www.ComputerBob.com/guides/connect_multiple_pcs_to_one_dsl_connection.php .
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by ComputerBob
October 10, 2007
Last Updated January 30, 2009
Anyone who has a lot of experience with connecting more than one computer to a DSL connection may think that it's an easy thing to do, but to people who have never done it before, the task can seem very complicated, confusing and difficult. This article explains the process in a way that even beginners can understand.
For the past few years, I've very happily used a low-cost DSL Internet connection in my home office. In all that time, I never had the need to have more than one computer connected to the Internet at the same time, so the single-port Westell 6100 DSL modem that came with my Verizon DSL service served me just fine. However, now one of my part-time jobs has provided me with a new Dell laptop computer, and I find myself needing to go online with it. For a few days, I accomplished that by physically switching my DSL modem's Cat 5e cable between the two computers, but I quickly grew tired of having to disable and re-enable each computer's network to get it to "see" the network each time I did that. So, like I always do, I researched the heck out of my options, and found the best solution for me.
One of my options was to buy a new multi-port DSL modem/router to replace my existing DSL modem. That would have cost me at least $60 (USD), plus $15 for two additional Cat 5e cables. In fact, the wireless modem/router that Verizon wanted to sell me would have cost $90. Either of those options would have allowed me to connect up to four computers to the Internet simultaneously.
Through researching the Westell 6100 online, I learned that it's not just a DSL modem — it's actually a modem/router, even though it can only be used with one computer. When I learned that, it reminded me that, back when I first got it, I had configured its NAT routing capability to close several unused ports, to provide an extra layer of protection between my computer and the Internet.
Important: The Westell 6100 has 2 different ports (ethernet and USB) on its back, but only one of those ports can be used at a time. You cannot connect 2 computers to it and have both computers on the Internet at the same time.
I also learned that because my Westell 6100 is already a router, then instead of buying an expensive multi-port router to replace it, I could choose to keep using the 6100, and buy an inexpensive ethernet hub that would add multiple computer ports to it. But when I shopped around for a hub locally, the cheapest one I found one would have cost $30, plus an additional $15 for two additional Cat 5e cables, bringing the total cost of that solution to at least $45. Just like the more-expensive modem/router option, the hub would have allowed me to connect up to four computers to the Internet simultaneously, but I wasn't sure that I'd be able to configure a hub to work correctly with the Westell 6100.
Then I remembered that, for the past few years, I've had a four-port D-Link DI-704P (rev B) router that someone had given me, sitting in a box in my closet. It's a wired model, but I prefer that to using a wireless router. After all, I don't need the convenience of connecting wirelessly, and I don't want the configuration, security and speed issues that come from using wireless connections. If I had wanted a wireless router, I could have bought a new one locally for $40 — only about $10 more than the cost of a multi-port hub.
I unpacked the D-Link router, connected my computers to it, and connected it to the Westell 6100, but it didn't work. All of its LEDs indicated that it was working, but my computers wouldn't connect to the Internet. In fact, my computers couldn't even display the router's configuration screen in their browsers, even after I rebooted them.
So I reconnected my desktop computer directly to my Westell 6100, went online again, and did more research on the topic for a couple of nights. By sifting through countless forum posts and snippets of networking tips, I finally figured out that the problem was caused by using two routers at the same time — I was connecting my computers to one router (the D-Link) which was then connected to a second router (the Westell 6100). There's probably a way to make that combination of routers work together, but if there is, I couldn't find it. The best solution I found was to simply disable the Westell 6100's NAT routing capability so that it would only function as a DSL modem/bridge. That way, the Westell 6100 would send a completely un-routed Internet connection to my D-Link router, and then my D-Link router would use its own NAT capability to route that one connection to my two computers. Here are easy to follow, step-by-step instructions that I used to configure the Westell 6100 as a bridge. I'll bet that if you did a Google search, you'd find similar instructions for bridging other popular models of single-port DSL modem/routers.
After I configured my Westell 6100 as a bridge, I rebooted my Westell 6100, my D-Link router, and both of my computers. Like most desktop computers these days, both of my computers are configured to automatically obtain their IP addresses through DHCP, so they both automatically got their new IP addresses from my router and connected to the Internet perfectly. In fact, without making any changes to either computer's configuration, I could go online with both my laptop running Windows XP and my desktop PC that dual-boots Linux and Windows XP. And both computers could view my D-Link router's configuration screen in their browsers.
Due to the security concerns that I described in my dual-boot article (see link, above), I intentionally did not enable file sharing on either of my computers. That way, even though my Linux and Windows computers will both have Internet access, they will be completely isolated from — and completely unaware of — each other.
Once I confirmed that both computers were online, I went to Shield's UP! and confirmed that my D-Link router gives both computers 100% "TruStealth" protection, even when I completely disable each computer's firewall software. While that's great to know, I'm going to keep the firewall software running on both computers anyway — it provides an additional layer of protection in case something or someone ever gets through my router's protection, and it doesn't have any noticeable affect on my Internet connection speed, according to several comparative tests that I conducted at Speedtest.net.
If I hadn't already owned my D-Link router, I probably would have bought a new wireless router, disabled its wireless signal and just used it as a wired router. That way, I'd still enjoy the additional security of using a wired router instead of a hub, plus I'd have the option to re-enable its wireless signal if my needs changed in the future.
So now I finally have a true office network, set up and secured exactly the way I want. It should make it more convenient to do a lot of things. For example from now on, whenever I make any structural changes to this web site in Linux on my desktop computer, I'll be able to immediately see how the changes look in Windows on my laptop computer. Yes, it took me a lot of time to figure out how to make everything work, but since I already had my D-Link router, my new network connectivity only cost me $7.50 — the price of one Cat 5e cable to connect my laptop to my router. And since my router has four ports, I have the option to easily connect two more computers to my network at any time in the future.
Update, January 30, 2009: After using the networking setup described above for a few months, the charity that I was working for asked for its laptop back. So I disconnected my D-Link router and reset my Westell 6100 back to its factory default configuration of acting as a modem/router.
I used that one-computer Internet connection for about another year, until one day, I needed to connect three computers to my Internet connection at the same time. Remembering the lessons of this article, I reconfigured the Westell 6100 to work as a bridge again, and reconnected my D-Link router. But I lost my Internet connection. No matter what I tried, I couldn't get my D-Link router to connect to the Internet with the Westell 6100 configured as a bridge. After trying unsuccessfully for several nights, I finally gave up was about to throw away the Westell 6100 and buy a new DSL modem — in fact, I had already looked online and gone to several local stores, looking for a replacement.
But then, on a hunch, I decided to reset the Westell 6100 back to its default setting of being a modem/router. That's when I was very pleasantly surprised — or, more correctly, shocked — to see that the Westell 6100 — in its default modem/router mode — "talked" to my D-Link router, which successfully connected all 3 computers to the Internet.
My local Verizon provider must have changed something in its DSL configuration during the year that I didn't use my D-Link router. So, for the past several days, my D-Link router has been succesfully connecting 3 computers to the Internet at the same time with my Westell 6100 set to its default modem/router configuration.
I'm sure glad I didn't throw away my Westell 6100.