Motorola MB8611 Reboots/Restarts Multiple Times a Day - PLEASE HELP!

@user_c5a405​ Update.  So much for my idea.  It has already rebooted once since I tightend the coax with a wrench.  Still waiting on a callback from Motorola.  Ha!

@Jlavaseur​ Yes, there could be a conflict, but in my case it's not in my network. If I connect my laptop directly to the modem it will still exhibit this behavior. My mb8611 performance is also impeccable, except when it's reconnecting to Comcast's network! It is reconnecting due to changes in the signal or possible direct commands from the DOCSIS network under Comcast's control. Nothing on my side is causing the reconnects. When it is connected, it is flawless.

@Jlavaseur​ I don't think so.  I've had this ASUS router for a few years now.  It's been running the same firmware since March/April last year.  There have been no further firmware updates from ASUS since.

I got this cable modem at the end of October.  It had been rock solid up until about a couple weeks ago.  The previous modem never had problems either, but Xfinity recommended that I upgrade my modem so I did.  

@Jlavaseur​ It's not that odd. I suspect Cox and Comcast operate similar equipment on their networks. It seems like a firmware issue or a change in line conditions that has made this particular modem (and possibly others?) prone to reconnects. I am quite confident it has nothing to do with the equipment on the LAN side. I see the exact same behavior whether I'm on my iPhone, my MacBook, my son's Windows PC, our Linux gaming PC, etc. All of these devices were running on the network flawlessly all summer, also. If I power off the modem, disconnect the LAN cable, and power it back on, it will start up just fine and negotiate a connection to the cable network. The status lights and a remote status check from the Xfinity app via cellular shows the modem online.

@Jlavaseur​ Sounds odd.  You're connecting your machine directly into the cable modem and booting between operating systems?  No router?

The only odd thing I did notice is that I had a constant ping going to a DNS server on the Internet in order to monitor connectivity.  At the same time I was in a Microsoft Teams call.  I noticed the ping stop, but the Teams call worked for several more seconds before it died.

@Jlavaseur​ I'm still within my 90 day window to return the modem through Amazon.  I think tomorrow I will see if I can put my old modem back in, make sure things are stable, and return the modem.  No use fighting with it when it seems nothing is going to be done about it anytime soon.  Motorola support still hasn't called me back and I got into the queue first thing this morning.

Wife left the house so I went ahead and put my old modem back in and I'm up and running again.  Gonna box up this MB8611 and return it.  Even if it's not the problem, there are known problems with this modem so I might as well get my money back while I can.

@Jlavaseur​ This is a DOCSIS cable modem we're talking about. Cox and Comcast (and pretty much every ISP in existence) both use optical signaling over fiber for the backbone of their network, but they serve the "last mile" connection to consumers predominantly using electromagnetic signaling via coaxial cable. That is the equipment in question here and is common across both carriers. I can rule out the interaction by watching the the cable connection drop and reestablish periodically by watching the indicator lights on the modem when nothing is connected to the LAN port. I do not have the time, patience, or inclination to do that right now because there is an overwhelming amount of evidence pointing to the issue being on the cable network which I have no control over. BTW, I am a software engineer with a significant amount of experience with networking technologies, but it has been a while since I stayed in a Holiday Inn Express :P

To be clear, the issue here is that the modem periodically disconnects and reconnects to the cable network. To troubleshoot any issue, you try to find the consistent conditions across occurrences of the issue to try and establish causality. Here's what I know:

• I can experience the issue with a different mix of devices on my side. It happens on WiFi, it happens on a wired connection. It happens with or without my switch in the wired path. It happens no matter what devices I'm using to access the internet. It happens no matter what application I'm using.
• I am unable to directly cause this issue by any pattern of usage on my side. It might happen halfway through watching a movie on Netflix, it might happen in the middle of a Zoom call. It might happen as I try to send an email.
• Whenever it does happen, I can access everything on my local network just fine, including the admin console for the model. Examining the state of the modem at the time of the issue always shows the same thing - a connection is in progress and the event logs show a consistent pattern. It appears that the modem is reacting to line conditions or other signals on the cable network side and the connection resets.
• Many other Comcast customers are reporting the same issues.
• I have not introduced new networking equipment or meaningfully changed my internet usage since this issue began for me.

Given this evidence, it makes more sense for Comcast to rule out an issue on their side than for me to start changing things on my side.

  Cox is fiber, same problem

It's HFC just like Comcast. A cable modem like the 8611 couldn't be used on an FTTP / FTTH connection.

@emattheis​ My modem, perhaps like others, doesn't just disconnect.  It reboots!  This really shouldn't happen.  This is evidenced by the clearing of the logs.  Motorola still hasn't called me back from this morning.  I still have until 1/31 to get my money back.  I put my old modem back in and I'm running again.  My 8611 is boxed and ready for return.  At this point, even if Motorola fixes the problem, I'm done with this particular modem.  Even if they do eventually fix this problem, who's to say that there won't be another problem?

Take a rest.

xxxxxxxxxxxxxx

@Jlavaseur​ 

You made an absolute statement.......

@Jlavaseur​ I appreciate the input! It’s helpful to have information from customer who don’t have the issue. I’d be curious to know if your modem is logging the same events that I see when my modem reconnects, if you’re willing to share.

@Jlavaseur​  Also curious to know what your connection page reports for system up time. When I compare the event logs and the system up time, I can see that the connection is resetting every time I see the logs reporting the pattern of events starting with “DS profile assignment change.” I can see that my connection is actually resetting a lot more than I notice. It only takes a few minutes to reconnect, so it’s only apparent when it happens in the middle of an activity that is actively trying to connect to the internet (e.g. - a video call, navigating to new pages on the web, playing an online game).

@Jlavaseur​ Interesting. Based on your reported experience and the log, it looks like when your modem logs the 'DS profile assignment change', the connection remains stable as the modem adjusts to the new profile. Presumably if you look at the uptime report, it will show that the modem stayed connected across the time of the profile change event in the log. When my modem exhibits the reconnecting behavior, it logs the profile change and three subsequent warnings.

If we look further up in the log, we see the 'Honoring MDD' notice (not shown in my screenshot, because I cut it off, but it is there along with the same diplexer mode change messages you show in your log). MDD is a 'MAC Domain Descriptor' and represents a message that is sent periodically on the cable network to instruct modems how to properly connect. The modem is responsible for adapting to the instructions in this message to properly connect to the network. My theory is that in certain segments of the Comcast network, MDD messages are being sent with parameters that the MB8611 does not tolerate, leading to a complete renegotiation of the connection and the intermittent connectivity issues some of us are seeing. In other segments of the network, the MDD parameters are tolerated just fine and no reconnection occurs. I suspect if I had been looking at the event logs a few months ago when my modem wasn't reconnecting, it would have looked much like yours, without the warnings.

@EG would love to hear your thoughts on that theory...

@emattheis​ I just found this thread searching for answers to my issues with the same modem. My log looks very similar to this one. My modem is disconnecting and reconnecting 2-5 times a day. What is the solution here? Buy a new modem or roll back to a stable firmware version(how do I do that)? Any advice is appreciated.