Modem frequently disconnects/reconnects

[EdPell]

Using Win 7 SP1, LinkSys CM3008 modem, LinkSys BEFSR41 router

I replaced a Spectrum-rented Motorola SB5101 modem with a LinkSys CM3008 I purchased. Occasionally, the Motorola would disconnect, but not often enough to concern me.

However, the CM3008 disconnects every day, several times a day. When it disconnects, it immediately attempts to reconnect and does so within a minute or so. Very irritating.

Is there a diagnostic procedure to determine the problem? If it's the nature of the beast, I'll just get another modem. There have been reports that the CM3008 overheats so I placed a thermometer on the case a few times - it never gets above 100 degrees.

Any advice would be appreciated.

Thanks
EdP

 

[Snick]

Hi EdPell,

How are you connected WiFi/Router or Ethernet?
Almost sounds like your Internet provider being that it occurred on two different modems to same ISP.
Do you have more than one device with the same problem?

 

[dg1261]

I had a very similar problem almost 18 months ago, from which I learned not all modems are created equal. Even though they're supposed to be compatible, my problem was only solved when I switched to a different modem.

You may ultimately have to buy a different modem, but the occasional dropouts with the rented SB5101 suggest there might be an underlying issue with your ISP's signal level, so I would suggest your first step should be to open a troubleshooting ticket with Spectrum. When they come out, maybe the tech can bring one of their modems to test with and confirm whether the problem is with your new modem.

In my case, I swapped a rented Arris TM822G modem* for a purchased Motorola MB7621. Almost immediately I had numerous disconnects, which came in swarms -- sometimes 20-30 in an hour, but then it would work fine for a day or so before repeating the pattern. I opened three different trouble tickets with my ISP over a one month period. Each time it would seem to work for a few days, but that may have just been coincidental and the disconnects returned. I eventually bought an Arris Surfboard SB6183, and the disconnects instantly disappeared. That was over a year ago, and all has been well since then.

All three modems were on my ISP's list of approved modems, but the MB7621 simply wasn't usable. I don't know if the modem was defective because I couldn't return it. Despite being only one month old and having purchased a SquareTrade warranty with it, the SquareTrade customer service (I use that term ironically) refused to honor the warranty. I'll never make that mistake again.

SquareTrade insisted the modem was fine and that the modem logs proved the problem was with the ISP. The ISP said they checked and rechecked everything and their system was working fine, so the problem had to be the modem. Given that the problems immediately disappeared with a different modem, it's clear SquareTrade was full of BS. I even confirmed by swapping back and forth between the MB7621 and SB6183. The dropouts returned when the MB7621 was connected, but clean when the SB6183 was reconnected. SquareTrade still refused to honor the warranty.

I opened three trouble tickets with my ISP over a one month period. Even though it ultimately wasn't their problem, they did find and correct two minor issues with my signal, so that's why I suggest you involve them. They found a signal level slightly lower than spec at the pole outside my house, and found an orphaned filter trap left inside my service box from another service call years ago.** It's unlikely either issue was bad enough to have caused the MB7621 problems, but it's nice to have them confirm I now have a good, strong signal.


* (The TM822G is a special telephony modem because I had cable telephone service. I couldn't find it available for purchase anywhere, so I opted to buy a non-telephony modem, discontinued the telephone service and switched to Vonage VoIP instead.)

** (In the old days, phone and internet services were split by a filter inside the locked service entry box, on the side of the house. Separate phone and internet cables then fed into the house from there. Eventually that was replaced by a telephony modem, in which the phone service was separated out inside the modem instead of at the service entrance. In my case, though, when they made that change the service tech neglected to remove the filter trap.)

 

[Snick]

dg1261

I agree with checking with ISP by contacting them for repair ticket, being that two different modems, presumably from different manufactures, are having the same issues!

Even if it was two different models from the same manufacturer would also point to ISP issues!

 

[file3456]

If your ISP is DSL, have the tech check for ingress in the drop.

Come to think of it, this can happen in cable, too.

 

[EdPell]

I apologize for the delay in thanking all of you. I *swear* the instant email notification was set when I posted, but I never got an email.

>How are you connected WiFi/Router or Ethernet?<
Well, the cable connects to the modem, the modem connects to the router, and the router connects to the PC.

> it occurred on two different modems to same ISP.<
That does make the ISP suspect, but it happened so infrequently with the rented modem, I just chalked it up to an occasional glitch and lived with it. It happens so frequently with the new modem I began to suspect the modem itself.

dg1261 - thanks for the comprehensive response. I made a note of the modem you're happy with, just in case.

The consensus of opinion is that I contact my ISP which I will do.

Thanks to all for responding and doing it so quickly.

EdP

 

[Snick]

EdPell

Please keep us informed. Knowledge is everything.

 

[samuria]

How long is the dhcp lease as it can drop when the lease is renewed

 

[dg1261]

I made a note of the modem you're happy with, just in case.

FTR, I'm not saying the SB6183 is necessarily a better product than the MB7621, only that it works better in my environment. The MB has a pretty good rating so it must work fine for a lot of people, but it wasn't very stable with my particular ISP and service. It's also technologically newer.

It's unfortunate that there's no way of knowing for sure unless you do a trial run with both. When you run into this kind of baffling, intermittent problem, what I'm suggesting is that you try a different brand (or, at least, model) of modem. It may not be conclusive if you merely replace one unit with another of the same model.

I'm a (now retired) PC consultant, and in my years of experience the Motorola Surfboard series had proven to be solid and dependable in many, many installations. For two decades I had purchased modems for my own home, as well -- and those were always Motorola Surfboards. But when my ISP deprecated the "split-tap-at-service-entry" topology, there were no telephony modems for purchase, and because I had phone service my only choice was to rent the modem from the ISP.

When I decided to replace my rented modem (after one too many price increases), I wanted to go with something with which I had prior experience ... but by then there was no "Motorola Surfboard" anymore.

Ironically, Motorola had sold the Surfboard line to Arris and started a new, MB-series model line. Faced with the dichotomy, I initially prioritized "Motorola" before "Surfboard", when I would have been better off the other way around.

 

[file3456]

Just to make sure you don't have a double NAT situation with the router and modem, go into command prompt and enter the following then post the results.

tracert 8.8.8.8