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Comcast cable internet disconnecting for unknown reasons

by scrubbynubby / June 25, 2006 3:32 PM PDT

I have had Comcast cable internet for about 3 years now and have always used the same RCA cable modem and have had no problems. Two months ago I first starting having a problem where the internet randomly disconnects but the modem is blinking exactly as it does when it's connected. I'd have to wait several hours before the internet would work again and had no clue why. This only happened about once a week so I figured it was comcast fixing something each time.

About a week ago it did this and did not come back on for over 24 hours. I called Comcast and asked them how to fix this and they told me to open up my Network Connections folder and disable Local Area Connection 2. After that I need to unplug my cable modem and plug it back in until the lights are all blinking as normal. I then have to enable Local Area Connection 2 and the internet works again.

I was glad to find a solution to the problem, but now this happens every several minutes! The problem seems to happen a lot more often when I am downloading torrents or other p2p files but this never used to happen. I've had to fix the problem four times while typing this message, can anybody help me? I'd like to rid myself of this problem or at least minimize it.

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The fact that you are using.....
by Michael Geist / June 25, 2006 9:10 PM PDT

a P2P sharing program points to some form of malware infestation. If this is the only PC on the LAN, try another. This will tell if the disconnects are related to your original PC, a faulty modem or an ISP issue.

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Old modem. . .
by Coryphaeus / June 25, 2006 9:29 PM PDT

Comcast has upgraded their system to a newer protocol. Some of the older modems are not compatible. The list of modems is at the Comcast site. And the new protocol enables faster speeds. I replaced my D-link DCM-200 to a new DCM-202 and my speed went from 3 Mb/s to over 6. And Comcast is in the process of upgrading again to an advertised 11 Mb/s.

Replace the modem.

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by scrubbynubby / June 25, 2006 11:44 PM PDT
In reply to: Old modem. . .

I'm not sure if I found the right list but my modem model(DCM305) was on the list of cable modems approved for use with the Comcast High-Speed Internet Service at

This list might not be up-to-date so could you please check if mine is on the list you were referring to or send me a link?

Also, I've tested my download speed and it's maxing out at only 1.5mbps when it was maxing out at 6.2mbps only a few months ago.

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What I found. . .
by Coryphaeus / June 26, 2006 12:47 AM PDT
In reply to: DCM305

Your modem is DOCSIS is 1.0/1.1 (the older cable protocol). The newer protocol is DOCSIS 2.0. Your modem is indeed approved for Comcast, but the newer protocol is needed to get the higher speeds. The D-link DCM-202 is DOCSIS 2.0 protocol.

I'd buy the D-link, try it, and if it works you're set. If it doesn't work, return it and we'll try another route.

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Why do you have 2 LAN connections?
by pratapan / June 25, 2006 11:36 PM PDT

Are they both DHCP? Does this mean you have 2 default gateways as well? Windows typically uses 1 gateway and never resorts to the second gateway until packet loss is detected.

My guess is that your P2P software is opening bunches of tcp sessions and you router can not handle it. Your $50 router can only track a certaing number of sessions. It seems many consumer routers stop functioning when the NAT limit is exceeded. Try turning it off or stop sharing your directory with others to cut down on sessions. Trace Route to yahoo or the DNS server when the problem happens to see if traffic even gets past your router. You should do this while the network is healthy and keep a copy handy for future reference.


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by scrubbynubby / June 26, 2006 12:15 AM PDT

I've always used Local Area Connection 2 as far back as I can remember. Local Area Connection is disabled and if I enable it I get an error saying "A network cable is unplugged". I don't worry about that because my internet has always worked fine with it disabled.

The internet disconnects often even when I'm not using P2P file sharing software but it only happens every 30 minutes or so instead of every 2 to 20 minutes while running P2P file sharing software. I've only been downloading 2 large files and used to download 10+ at a time without a problem. I'm basically downloading files I wont be able to download when I relocate in 3 weeks and cancel my comcast subscription. I really see no benefit in buying a new modem, if that is the cause of the problem, just to use it for 3 weeks.

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when was the last time you scanned for Virus?
by pratapan / June 26, 2006 11:35 AM PDT
In reply to: Dunno

Some Virus do port scans looking for a new target to infect. This can have the same effect as P2P software opening many TCP connections and crashing the router.
When in doubt, download the free Ethereal scanner and capture everything in/out of your PC ethernet card.
Shut down all browsers and mail and just scann your ethernet and see what traffic generates on its own. This will give you a hint of what is going on. I seriously doubt the problem is Comcast.

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