Strange cable modem problem

I’ve been a Comcast customer for about 5 months, and throughout that time my family has had 2 to 4 computers hooked up to the cable modem through a hub. There’s no router; we get IP addresses from Comcast’s DHCP, and they tend to be on separate subnets.

For about the past 10 days, my computer has had a problem. I’ll be sitting on the internet, browsing the web, chatting on IRC/AIM or whatever, and the connection will suddenly die. I can’t access the internet at all, though I can still access the other computers on my LAN. It happens at least once a day, often three or four times, but there doesn’t seem to be anything specific that triggers the problem. When the connection on my own computer is dead, I can still use the internet from the other computers - I’ve never seen the connection die on the other computers.

If I click the “repair” button in Windows XP, the problem is solved. Windows renews the 4-day lease on my IP address (the same one I’ve had for weeks) and the connection is fine again, at least for a while. Sometimes, it seems to fix itself after 20 or 30 minutes, if I’m not there to fix it by hand.

Comcast claims that nothing on their end would cause this problem. They mentioned that they might start “purging” multiple IP addresses from customers who haven’t paid for extra addresses, but only once a week and they haven’t even started doing it yet.

Their first suggestion was to uninstall my NIC from Device Manager and let Windows reinstall the driver. Didn’t help.

I did some Googling and found out that some cable providers send a “heartbeat” packet to see if you’re still using the address, and that firewalls can block it. I turned off XP’s firewall. Didn’t help.

Comcast has blamed my hardware and suggested changing my network cable, which I haven’t done (I’d have to swipe one from somewhere). I don’t see how the NIC or cable could be causing the problem, since (1) I can fix it just by clicking Repair, so obviously I can still contact the DHCP server, and (2) I can access the other computers on my LAN with NetBEUI (but not with TCP/IP).

I haven’t been able to solve the problem, and neither have Comcast or my techie friends, so I’m posing the question to the SDMB. Is there anything I could test to narrow down the problem? What could be causing these periodic dropouts?

bump

I used to have the same exact problem… but when I called Time Warner they asked me what modem I had and then said that they stopped using that modem 6 months ago and they needed to bring me a new one.

My connection just started doing the same thing this past week.My modem is fairly new so I know that’s not the problem.Maybe it’s a Comcast thing… I sure am tired of having to go into network places to repair the connection.If anybody has a clue I’d also appreciate it.

I have a similar problem, and usually just fix it by unplugging the modem and rebooting the computer. I asked this question to the Straight Dope a few months ago - maybe you can find useful info in that thread: http://boards.straightdope.com/sdmb/showthread.php?s=&threadid=155869&highlight=bob55+cable+modem