Motorola MB8611 modem keeps restarting - firmware issue

I do think something is going on, but it's not a universal problem. I got an MB8611 on December 8, 2022, along with Xfinity Internet service starting on the 9th. My modem firmware was at 8611-19.2.20 when I got it. On January 2, 2023, my firmware was updated to 8611-21.3.7. I had no issues with the previous version. The was up from the day of installation until the firmware update rebooted it (~ three weeks). It has been up since that update without any issues, except when I rebooted it a few times (from the MB8611 Security button to reboot). I did that because I noticed that a script on my firewall/router wasn't getting executed at the correct time, and, therefore, didn't reliably pick up the correct WAN IP address. Since I fixed the script a few days ago, the cable modem (CM) is up and solid for me.

So I'm wondering what is happening for everyone else. Especially the toggling between 8611-19.2.20 and 8611-21.3.7. If the firmware file were corrupt when the cable modem got it from the Xfinity file server, I would expect it to reject it outright. (That's assuming the file is checked by a checksum or the like.) Since the firmware gets applied, I assume it was OK. At this point, it should be stored in the CM's NAND memory (i.e., permanent memory akin to an SSD). You should be able to reboot it dozens of times without reverting back to the previous version. Since it does, maybe the firmware update had an issue (like failing a secondary checksum test). Another possibility is the CM's NAND memory is bad, the firmware is corrupted, and it can't be loaded correctly. In this case, reverting to the factory default - 8611-19.2.20 - would be a way to recover. (The latter would be covered by the warranty. I have no idea how to test that.)

I'm also starting to wonder if the new firmware version is less tolerant of issues with the coax signal than the predecessor. That could be causing the CM to reboot in an attempt to recover. Just for fun, here are the current Connection statistics for my MB8611. Compare them to what you see on yours. I'd be curious what the differences are.

I too have been experiencing the same issues with my mb8611. It has been a pretty solid modem but within the last couple months, the amounts of disconnects/reboots has gone up quite alot. I've noticed mine is constantly upgrading/downgrading the firmware as well.

I was fed up with this (thought it was an issue with Xfinity) and the data cap so I switched over to WOW. Well the modem is doing the same exact thing on WOW's network. This leads me to believe that it is 100% an issue with the modem. WOW provides a free gateway with their 1.2gb plan (and no data caps) so I'll be switching over to their free modem tomorrow to stop this annoying issue. 

My suggestion for others with this modem is to get rid of it.

I have the mb8611 with current firmware 21.3.7, performs flawlessly for me, if your convinced its the firmware reboot it with nothing attached to it for a test, or at a minimum just a firestick or similar,for some activity,  no router, computer etc, if it still reboots i would suspect firmware and or modem, if it doesn't you solved your problem....

I just called and spoke to Motorola customer support and the lady (Jillian, super friendly btw!) told me that they are well aware of the firmware issue on some mb8611 modems and asked if I had Xfinity service. They are shipping me a new modem and I have to return the old one within 30 days. She said the new modem should not be affected by the firmware issue.

@user_2edda3  It would eliminate any possibility of a conflict on your network, it might not make sense to you, but mine works…

@user_2edda3  How would you actually know if you didn’t try, yet again mine works flawlessly…. 

Absolutely not, but I did spend a couple of nights in a Holiday Inn Express….

@user_2edda3  You tried WOW, different isp, they probably downloaded to your modem there version of the firmware, yet your equipment is probably all hooked up in the exact same configuration, same issue….

Hello @user_d77dfd
Thanks for reaching out to us here on the Xfinity Forums for support with this issue. Reviewing this thread, it sounds like it may be an issue with the modem itself, but if you would like, we would be more than happy to check over everything on our end as well just to be sure nothing gets missed. :)
Feel free to send us a DM with your first/last name and service address so we can help! 

To send a Direct Message, please click on the chat icon on the top right of this page, next to the bell. Make sure to send the message to our singular handle "Xfinity Support" and we will get back to you ASAP.

Hmm, I'm having the exacts same sort of issue with my Motorola MB8611, although it is connected to a router.

How are you guys figuring out what firmware, etc it has on it?   Do I need to connect a laptop direct to the modem itself (bypassing my router)?

I did just order a 3.1 Arris modem but it hasn't shown up yet.  

@user_2edda3 please let us know how that replacement modem works out!

Add me to the growing this of people with the MB8611 and these disconnects.  Everything was fine until I upgraded the modem (which the only reason I did so was because Comcast claims my existing modem would no longer be supported).  The MB8611 is listed as a compatible modem, right??

I noticed this in my log this morning.  Any significance to this?

EDIT: whoops!  wasn't thinking about PI.

The log entry was of a "Notice" level indicating that a "DS profile assignment change".  I haven't seen such messages previously.  My connection has been stable today, but it might be a fluke.

It's a firmware incomplatibility issue with the Comcast network as configured.

Moto needs to sync with Xfinity Comcast & get the  right config code & send out to all 8611 owners an updated firmware & installation instruction.

There's nothing wrong with the hardware unless the Moto 8611 Firmware is soldered into its memory by hand indiviually (j/k) or there is no way to update the firmware via software patches due to lack of memory - only then can I understand  why people think this is a reason to throw out this expensive & up to this point bulletproof piece of hardware.

@GuyHeartCable I tend to agree, my mb8611 works perfectly with the same firmware, so it’s rather confusing…

I have an older Arris non DOCSIS 3.1 modem in-hand, and another Arris 3.1 on order.  I'm going to see if I can figure out a way to get the old one to work instead of the Motorola.     Just plugging it in DOESN'T seem to work, so it probably requires some XFINITY cooperation of some kind (arghh).   You would think there would be some standard handshake protocol in which xfinity figures out what modem is out there and auto configures, but, no.