Router problems
February 2, 2007 8:08 PM   Subscribe

I need help figuring out why I cannot share a cable connection with my router.

Ok, here's the situation, my friend has a cable modem which he uses to connect to the internet. We want to share the connection to a second computer so we bought a router and connected both computers to the router and the router to the cable modem.

The router is a Linksys BEFSR41 v4 and when a single computer is connected to it the internet works perfectly. However the instant we connect the second computer to the router, the connection on both goes haywire, disconnecting every 4 seconds or so. After spending 2 hours with technical support they suggested returning the router, saying that it was probably a hardware problem with the router itself.

However, this is the second router to give me this problem; the first one I tried was a D-Link EBR-2310 and after 2 hours on the phone with their tech support they also told me to return it. Therefore I'm thinking that the problem may not be the router but perhaps the modem itself, is it possible that the modem for the cable connection has compatibility issues with my router?

If anyone has any suggestions, or can point me in the direction of a good techie forum, I'd love to hear it. I've tried everything I can think of, and I am getting very frustrated.
posted by Vindaloo to Computers & Internet (9 answers total)
Have you made sure that the router is cloning the same MAC (physical) address of the computer that was originally directly connected to the cable modem?

Many cable companies require that the MAC address be registered with their router on their end, and won't give you an IP (or won't keep your connection live for long) if you're connecting with a device with a different MAC address.

My linksys has a simply MAC cloning feature in its little web-admin tool.
posted by chimaera at 8:43 PM on February 2, 2007

Both computers are set to obtain IPs automatically? (i.e., to use DHCP?) Cable connection going to the right (uplink) port on the router? Is the router able to get an IP from your ISP? Are you sure it's a proper internet IP? (i.e. no 192.168.x.x). Can you tell us what all three IPs (i.e., each computer's and the router's) are?
posted by limon at 9:22 PM on February 2, 2007

If either or both the client computers are Windows 2000 or XP machines, from a command prompt, do ipconfig /all, then copy and paste the results to this thread. You can find a combination file/edit menu in the top left corner of a WinXP command prompt window that will allow you to Edit-->Select All and then Edit-->Copy to get this on your clipboard. With this information, we can give you specific configuration advice, or further suggestions. Without information from you regarding O/S and TCP/IP settings on your client computers, we're just shooting in the dark.
posted by paulsc at 9:48 PM on February 2, 2007

Two things: One, searching on Google for the router name (Linksys BEFSR41 v4) suggests that others are having connection issues as well. It very well could be the router, though no idea about the other ones you tried.

Two: you probably have a "WAN" or "Internet" jack in the back. Don't use it. In almost every internect configuration that involves home connects, it won't work properly, if it works at all. Plug the modem into a normal computer jack - I've seen similar problems fixed after days of trouble shooting by switching the jack. (Yes, computers are weird like this).

Hope you get it working!
posted by niles at 10:31 PM on February 2, 2007

back = back of router
connects = connections

posted by niles at 10:32 PM on February 2, 2007

Many cable modems are, in fact, routers in their own right, but only have a single physical Ethernet port on the LAN side. If your friend's cable modem is like this, then it would most likely connect to your friend's PC via an Ethernet cable, and your friend wouldn't need any cable-company-specific configuration stuff on his PC to get connected - all the required configuration information would be held inside the modem/router, and you'd typically be able to get at it via a little administrative web server built into the modem. On the PC, all you'd see is a normal LAN connection.

If this is in fact what he has, then you don't need another router in order to share the connection - a simple Ethernet switch will do the job, and have far less stuff to go wrong. So you should take tech support's advice, return the router, and replace it with a switch. Something like a D-Link DES-1008D desktop switch is fine.

This is basically equivalent to the LAN-port-only configuration that niles recommends, except that instead of using an expensive router to act as a cheap switch, you're using a cheap switch. It will also be more reliable, because there is no chance that your PC's will end up acquiring their LAN IP addresses from the wrong router.

OTOH if it really is just a modem, you'll find a PPPoE connection configured on the PC to make it work; that connection will have cable-company-specific info in it like a username and password and whatnot. If you simply duplicate those connection settings on the second computer, your computers will be fighting each other to establish an exclusive point-to-point link to your ISP's head-end router, and you'll see the behaviour you describe.

In this case you do need a router to share the connection, and you need to change the way your PC's are configured.

First, you need to disconnect the cable modem from the cable.

Then, you need to plug the first PC into a LAN port on the router, and connect the router's WAN port to the cable modem.

Next, open the router's admin webpage with a web browser on the PC, and find where the PPPoE settings are at.

Next, open the property sheet of the PPPoE connection on the PC, and use the information there to configure the router's PPPoE settings appropriately. One of the required settings may well be the original PC's MAC address, as chimaera observed.

Next, disable the PPPoE connection on the PC; establishing the PPPoE connection is now the router's job.

Plug the cable modem back onto the cable and see if the PC can now get to the internet via the same LAN connection you've been using to talk to the admin webserver.

Next, disable any PPPoE connections on the second PC, plug it into another LAN port on the router, and you should be good to go.
posted by flabdablet at 11:27 PM on February 2, 2007

Response by poster: The connection does not require a user name/password or a MAC address, as both computers can access the internet fine through the modem alone, or through the router and modem. However the problem occurs when both computers are connected to the router.

And trust me, every single option of configuration on the PCs and/or router has been tried numerous times to no effect. That is why I was thinking it was a modem problem now.

I will try Niles idea tonight, hopefully that will do the trick.
posted by Vindaloo at 9:10 AM on February 3, 2007

If you continue to have trouble, and would like more help fixing it, then as well as the information that limon and paulsc asked for, it would be helpful to see the routing tables in use on each PC, both when it's working and when it's having trouble - four tables in all.

To capture the routing table, type

route print >routes.txt

into a cmd window, then paste the contents of routes.txt here.
posted by flabdablet at 2:27 PM on February 3, 2007

you actually may just have a weak signal. i once had a situation where i couldn't use my modem and my cable box at the same time, and the problem was that our house wasn't getting enough signal. it eventually resolved itself when the cable company upgraded its equipment, so i'm not sure what you can do if that's the problem.

it can be hard to diagnose until you try to split it too many times.
posted by thinkingwoman at 8:40 PM on February 3, 2007

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