new router will not stay connected to Arris cable modem & modem resets

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A standard comcast answer, when you don't want to pay the ransom for their equipment.  I have been trying to get a netgear router with  builtin vpn working.  I have spent hours trouble shooting with the people that built the router, I have spent hours trouble shooting with the the  vpn provider and nothing on their end seems to be a problem.  The issue seems to be with comcast not wanting customers using vpns, so the only work around I have found at this point is to connect the vpn router thru another router.

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Yes, I know it doesn't make sense.  That is why I need help. 🙂 

I barely know anything about networking (big surprise), so this may sound absurd but...  Maybe comcast registers router MAC addresses and won't allow a new one?  I tried cloning my PCs mac address to the router but the same disconnect happened.

again, The VPN features on the D-Link DSR-250 router are off by default (so I am told by D-link support).  I have no idea why the router cannot keep a connection with the modem.  When I plug in my older, non-vpn routers to the same modem everything works fine.

*I'll check with Arris.

*Update:  Arris said I could try a factory reset on the modem.  If that doesn't work, Arris said contact D-Link.  D-Link said contact comcast.  Comcast said contact Arris.   welp...  Guess I'll try a factory reset tomorrow and if that doesn't work I'll call comcast.  LOL!

The modem reset didn't work and neither did cloning the pc MAC address to the router as suggested by product support...

After much trial and error and Xfinity sending out a tech after I purchased a new modem the problems with using new wired routers was still not resolved.  I told them it appears they are blocking me from using new hardware.  They said they do not do that.  However, long story short:  I discovered Comcast is only allowing me a single mac address from my old 2006 router and any other router I plug in will not work (I've tried 4 wired routers) unless I input the old mac address of the 2006 router into the new router.  I finally figured that out on my own and that is the only thing that allowed me to install a new router.  Resetting the modem and installing a new modem did not help, the lock out goes back to their internal systems it appears.

If you are having problems installing new routers Comcast may have locked you in to only one old mac address.   They must add your new hardware's mac address into their system.  Comcast is still in denial about it, but I will try calling them back and explaining it again.  

I don't want to be locked in to one single mac address from a 15 year old router.  In this case if I lose that number my internet will never work again...

Hello and thank you! I really appreciate you being a member of the Comcast Family! Can you please send me a PM with your first and last name so I may further assist you with the make and model number of your modem? To send a private message, please click my name "ComcastThomasF" then select "Send a Message" on the right side.

What is the exact make and model number of the cable modem ?

@bpren 

As asked, What is the exact make and model number of the cable modem ?

If it is a straight / plain vanilla cable modem, you need to power cycle/re-boot the modem each and every time that you change the device that is being directly connected to it in order for that device to be able to get an internet connection.

And please post the info here in the open forums so that all readers here may benefit from the exchange. This is in keeping with the spirit for which these public help forums were originally intended. Thank you.

The modem was power cycled several times,  (even unplugged for 24 hours) and comcast support reset it as well.  I also purchased a new modem a few days ago (Motorola MB7621).  I had tech support in my home yesterday and they would not fix the problem.  

This all happened because I was trying to replace a very old failing router.  This was tested with 4 brand new wired routers from TPLink, Ubiquiti, Apple and D-Link.  Each wired router would connect to the cable modem and get internet access for a brief moment and was then blocked and unable to connect to the internet.  I settled on keeping the 8-port D-Link DSR-250 router with the hopes I could get it to work.

Again, The cable modem was connected, receiving signal and working fine but NO routers other than my very old router (circa 2006) would stay connected.  My new dsr-250 router finally worked once I entered my old 2006 router's mac address into it.  Therefore, Comcast has only allowed me 1 mac address and has locked me out from any new routers with a different mac address number.

I repeat:  Everything is working fine now once my new router had my old router mac applied to it.