Netgear N600 and DOCSIS 3.0

I've been in IT Infrastructure and Operations world for more 15 years now, helping companies and folks to resolve all sorts of performance issues. Here is my horrible experience with internet connection @ home :)

I have been using ATT for almost a decade and finally decided to go to Comcast.
I upgraded to a DOCSIS 3.0 Motorola modem SB6120 router and also bought a Netgear N600 wireless dual band router for Comcast internet to avoid any monthly charges at all.

Configured and customized router to whatever I wanted, internet all good. By the way I have CAT 6 structured wiring at my home covers almost all the rooms.

The problem I was having was that when connecting to the internet through the wifi,
there was a lag and websites would load way slower.

Symptoms:
Frankly I didn't notice any lags, however my wife started complaining that her vpn drops connection after we switched to Comcast. And its horribly slow compared to AT&T. We were ATT Pro which was 3mbps and Comcast promised at least 10 mbps. Speedtest confirm its double the speed, it never resulted in less than 22mbps. Now, mathematically there is no way internet will be slow. So, I ignore the problem. The complain continues so finally I decided to spend some time with issue.

I still cannot see the difference visually with google.com or yahoo.com

But, yes it can be better there is some lag of 3-5 seconds while pulling the site which may be annoying to some.
The problem became very obvious when I started a download, it was 70KB/s, that means my internet speed is only 560kbps


Troubleshooting steps:
#Packet loss:
The first thing i noticed was the packet loss. While pinging the router after every 25 packets of 1ms latency there are 4 packets which is 100ms. Called Netgear, spend couple of hrs. with tech support, they tried lots of combination with no security, changing to different channels, (I believe 6 and 11 are reliable :-)), I had already downloaded inSSIDer to see if there is any interference with channels neighbors are using, recycle the modem, re flash the modem etc. finally changed default fragmentation length from 2346 to 2345 and there was some improvement in packet loss. But ultimately gave up.

#Wireless speed test
Tried a speedtest using wireless, it says 22Mbps however download sucks (50-100 KB/s)

#Wired speedtest
Tried a speedtest directly connecting to router, it says 22Mbps however download still sucks (50-100 KB/s)

#Connected directly to modem
Now connected directly to modem, speedtest is good 27mbps and so is the download speed (2.4 MB/s)
so now the problem boils down to router.

I google'd the Netgear problem with Comcast and found that we have disable WWM for Netgear. It was already disabled when I had initially configured it. Again played with few things no change. There were lot of suggestion to change the router and go with Comcast router.

However, I decided to reset the router again. used all the default option to connect wirelessly.

What's the download speed 4MB/s !!

Now I have backup of N600 old config and new config which works with expected speed. The problem is the netgear.cfg is encrypted and so do we want to solve this problem now. May be .. whenever time permits next time..

I took me more than a month to solve my home internet speed :(