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New Visitor
Posts: 3
Registered: ‎07-25-2009

SOLVED - router/laptop works from one cable modem not another

[ Edited ]

The initial problem

A friend of mine (also on Comcast) was having trouble with a netgear router being flakey and getting knocked off wireless periodically.  Since she lived in an apartment complex and I saw many other wireless routers on the same channel I aimed to change the wireless channel.  Dell laptop running Windows XP was slow but otherwise functional on a wireless connection.

 

Couldn't Get into admin on router

Password unknown.  Since this was going to take a reset and she also had some problems with the laptop, I took the router aand laptop back to my place.

 

Setup the Router again and plugged into my Comcast modem. 

Everything works now, wireless, wired etc.  After a little work on the laptop things are working nicely.  Power cycled and everything is still good.

 

Brought everything back, plugged into her Comcast modem - Problems!!!

Laptop connects wirelessly, or via ethernet, however no internet access.  Browser acted as if there was no DNS however an ipconfig /all showed dns assignements.

Unplugged router and plugged laptop directly into the cable modem with an ethernet cable... everything works!

 

I'm stumped.  Have never seen anything like this before.  I have the feeling i'm missing something really simple and stupid here but what?  Is there some issue with the modem that makes it not want to talk to the router?

 

Ideas?

 

Rich

Connection Expert
EG
Posts: 43,708
Registered: ‎12-24-2003

Re: Geek Challenge: I'm stumped - router/laptop works from one cable modem not anothe

[ Edited ]

Are you properly powercycling the modems each and every time that you are changing the devices that are being connected directly to them ?

New Visitor
Posts: 3
Registered: ‎07-25-2009

Re: Geek Challenge: I'm stumped - router/laptop works from one cable modem not anothe

Tried removing power to the modem, but this is designed to service phones as well and removing power doesn't seem to deenergize anything.  Battery backup? 

 

The only way to reset the modem is to call comcast and ask for a modem reset over the phone.  I did try that by the way but it didn't help.  But again the modem works directly connected to the laptop.

 

Never seen a problem like this before.

Connection Expert
EG
Posts: 43,708
Registered: ‎12-24-2003

Re: Geek Challenge: I'm stumped - router/laptop works from one cable modem not anothe

Yes. If you are using a telephony type modem that has a built in backup battery then just removing the A.C. power will not powercycle it. You need to use the recessed reset button on the rear. You'll need something like a bent paper clip or the tip of a pen to do so. Alternately you can both remove the battery and the A.C. power to reset it. 

New Visitor
Posts: 3
Registered: ‎07-25-2009

Re: Geek Challenge: I'm stumped - router/laptop works from one cable modem not anothe

That did it.  Thanks. I'm surprised the modem is that sensitive.  Not sure why it wasn't needed when I plugged into mine though. 

Connection Expert
EG
Posts: 43,708
Registered: ‎12-24-2003

Re: Geek Challenge: I'm stumped - router/laptop works from one cable modem not anothe

[ Edited ]

Glad that worked for you ! It's not that it is "sensitive". The modem stores the hardware MAC (Media Access Control) address of the last device that was directly connected to it. It is deliberate that it has a MAC address cache that can only be cleared via a powercycle operation. CC supplies only a single IP address to a residential connection.