isp's dhcp does not function properly

@XfinityAaron Unfortunately not.  It just no longer works in bridge mode.  I can't find anybody at Xfinity with the technical skills to investigate the problem.

I would like to get your account pulled up so we can take a deeper dive into what is going on. Please send me a direct message with your first and last name, along with your complete service address to “Xfinity Support”. To do so, click on the chat icon located at the top right of this forums page.   

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@XfinityAaron I found something rather interesting. 

When the X1 was added back to my account, I had a single old computer connected to it for testing the connection.  When the X1 was operational again, I unplugged the old computer and plugged in my Asus router.  That also worked, while the X1 was in router mode.  As soon as I put it back in bridge mode, the Asus gave the error message again that the DHCP server isn't functioning.  So I went in to the Asus, and cloned the MAC address from the old computer that I had been testing with when the X1 was re-added.  As soon as I cloned that MAC and rebooted, everything started working.

That's why I'm convinced the DHCP server is locking the MAC address.  Is that something you can check?  Seems rather an odd coincidence if that's all it is.

@Bgood2 Thanks for that information, just to be sure, do you mean the xfi Xb6 modem? The X1 is our TV box. You mentioned this started a couple weeks ago. Was it working properly before that?

Well, I thought the modem was called X1.  Sorry.  It's the black monolithic tower with the single light on the top surface and the right-hand side.  Looks like it's an Arris TG3482G.  It had been working fine in bridge mode most of the time in the past 3 or so years.  I believe I had one or two other occasions where it broke suddenly, but Asus added a DHCP mode called "Continuous" that resolved it for ages.  Then suddenly about 10 days ago, the DHCP problem returned.  It turns out that by having my Asus router impersonate the MAC of the computer I had previously directly connected to the Arris TG3482G modem, the Asus was finally able to get an IP address.  This is what leads me to believe there is something "locking" the MAC address within the DHCP server.

@andyross Putting in a bogus MAC seems to have worked just fine! :)

I have been told that is not a good idea as it can possibly conflict with another. A week or so from now, you can try restoring the original address and see if it now works.

@Bgood2

FWIW, always try using MAC addresses from devices that you actually own, not made up ones. As was stated, it's not good practice. 

I'll pull a MAC from something I own then.  I don't think a collision is likely, but it's not impossible.  For what it's worth, there was a maintenance in my area today "to improve service" that knocked my modem offline this afternoon.  Nearly two hours on the phone with Comcast and they wanted *again* to send someone to check the signal strength on my cable outlet (that was checked by a Tech just two days ago and found to be fine).  Arrrrrggggghh.  So I went back to the Comcast rental modem which, magically, works.  So if you're keeping score at home, *4* modems I've bought (from the Comcast-approved list) have either failed to work from the start or failed to work more than a week, while *2* Comcast rental modems work/worked just fine.  It's almost as if Comcast has a financial incentive to make sure I pay them $14 every month forever, rather than letting me use my own modem.  Hmmmm.

Frankly, I think Comcast should be forced to let me use their modem free of charge unless and until they can find a model that I can buy to replace it.  I'll be calling the Comcast regulator in my city this week to discuss the whole situation.  I've bought the Comcast modem many times over with my rental fees and I'm tired of how this always plays out the same way.

@user_40776f idk exactly who in this building that has done this but this is wrong