Which way is your machine connected to WNDR3800 -- through wired or wireless ?

Can you try this using wired medium ?

Did you try with other router ? It may happen that the internet connection itself has some problem.

When internet is disconnected are you able to ping to WNDR3800 ? Is there any periodic interval between two consecutive disconnection ?
I am trying to find the cause of this problem.
At the time disconnection what is shown in Web UI of WNDR3800 ? Can you send us the screenshots ?

Okay. I will test it with my router and share my experience. What is the frequency of disconnection ?

Koen said: I'm having exactly the same issue! All the lights are blinking on the router as if it behaves normal, except Genie is telling me it's disconnected from the internet and Windows is telling me it's disconnected from the internet. Also I don't have any LAN connectivity (times out everything) I'm printing on a network printer, but doesn't work (only start working again after power cycle) if I power cycle the router everything is Oké. The internet modem is Oké. I tried resetting the router to factory defaults, but problem is still there.

My initial configuration was 5 Ghz only with the 2.3 Ghz completely off. On my network I had 2 Macbook Pros (MBP) at 5 GHz, using time machine over the wireless to the Seagate Goflex NAS. I also have 1 Sony Blueray running wireless 5 Ghz, and three devices wired in: another Sony blueray, the NAS, and a Tivo. The blueray and the NAS are at 1000 Mbit, the Tivo at 100 Mbit.

I enabled the 2.3 Ghz stepped the MBPs down to 2.3 Ghz and I am no longer having problems. I am unhappy with this solution and will debug further. My kids use the wireless Blueray and they are complaining about Netflix load errors, but that could be anything.

I suspect the software and might give DD-WRT a try to see if that changes the behavior.