MB8611 Problems

@petmitsu​ Put old modem back online.  Returned MB8611 and got my money back.  Problem solved!

@XfinityVianney​ Yes I can confirm that I have been getting frequent T3 timeouts on the MB8611. It is extremely unreliable happening multiple times a day. Given my recent move and the modem being the only piece that made it to a completely new network setup I am confident that this modem does not work on the Xfinity network. I have also seen a few posts in this forum and on Reddit regarding this modem. If there is no fix it should probably be removed from the approved hardware list.

Thank you for that suggestion. We update the list regularly so we may make that change once we do more investigating. I apologize that you are having these issues. I think replacing it with a different model may e the way to go. 

@XfinityVianney​ if I understand other posts on this thread correctly... the issues folks are reporting are the result of Comcast pushing a firmware update to MB8611 modems that has caused them to start malfunctioning?

The MB8611 that has been used to provide service to my house for about 2 years begun to drop its upstream connection near the end of 2022.  It is so bad that we have pleaded with Comcast to send Comcast field technicians to the house.  The technicians have determined that "everything is working fine with your physical connection, it must be something downstream of your modem", but they have never seen the outages occur.  When the connection upstream from the modem is lost, all status lights on the modem turn off except for the power light nearly every time.  Sometimes some or all of the lights stay on during an outage, but those type of outages don't occur as often.  It has now gotten to the point that the internet connection between the Comcast network and the modem is lost multiple times per hour. 

In the past hour alone, the connection has dropped sixteen times. 

I live in a rural area.  There is no reliable cell phone coverage near my house.  My family and I rely on our Comcast internet connection for all home communications.  Phone calls.  Video calls.  Emails.  Text messages.  Streaming television.  Apps.  An Internet connection that drops SIXTEEN TIMES IN AN HOUR is not usable.  With the current state of the Comcast internet connection to my house, the connection cannot be relied on for anything.  There's a difference between outages being annoying and outages becoming a safety issue.  We are well past the point of the frequency and duration of outages being a safety problem.  If I do not have a working Internet connection to my house, the quickest way for me to access the Internet (or to call 911, for example) is to drive about 10 miles from my house so I can hotspot off of my mobile phone.

I need a reliable Internet connection.  How can I achieve a reliable connection to the Internet via the Comcast network?

(I should not have to purchase another modem because Comcast pushed firmware to my modem that made it begin behaving this unreliably...)

These are relevant logs from my MB8611.

It seems like Comcast and Motorola have no interest in resolving this issue anytime soon so I would suggest you take matters into your own hands and get another brand and model modem. If you don't want to spend too much, get a refurbished one from ebay. There's a good selection with very affordable prices. I reactivated my old Motorola SB6120 when my MB8611 got bricked due to a firmware they pushed onto it while trying to troubleshoot this issue and it got me through a few days until I was able to get a different modem. So get on ebay!

@Jlavaseur​ Whats your secret?

The modem is rebooting I can see the lights going through their usual dance. I cannot login to the MB8611 admin page through my router and need to plug directly into the modem to access it. That issue is something with the subnet being different than my network.

It could be my router but I doubt it. That is the only thing that also made the move with me. I am currently using an old SB6121 modem on the same setup without issue.

The MB8611 has caused me a years worth of head ache and I am ready to move on. Maybe Starlink is a more reliable option for my needs, I don't think satellites get hit by trees.

@steelesh8114​ the CM1000 only has a 1Gbs port, right? I bought the MB8611 specifically to get the full 1.2 Gbps speed to my router over the 2.5Gbs link. Comcast lists the Netgear CM2000 for my plan, and it’s quite a bit more expensive than the Motorola MB8611 or the Arris S33.

I ended up getting a CM2000. Totally overpriced, but I use a Netgear WiFi router and I like it, so whatever. After a few restarts to get it activated, it's been rock solid for 24+ hours with no errors in the logs. 

@cajual​ Thanks for the feedback. Guess I’m going to buy a new modem and hope it doesn’t suffer a similar fate in time. Really annoying since the modem worked fine for months, still works fine for some customers, is listed as compatible by Comcast, and is advertised as such by Motorola. Hard to not see this as a way for Comcast to force customers into renting their equipment.

@cajual​ agree same here, I tried the replacement modem (MB8611) that motorola support sent me and I had the same exact problem (intermittent resets). Switched back to my older DOCSIS 3.0 modem and things are stable. Comcast Docsis3.1 with Motorola mb8611 has BIG problem and none of these companies want to fix this problem. Pathetic.

@user_8936c5​ Yes.  I have been using my MB8611 for a few years without much problem, but I start having intermittent connection issue since a few weeks ago.  I find the version of firmware is 21.3.7 so I bet they pushed out the update recently in my area. Not sure how to fix it. 

@Oregon_Trail​ The latter. Even if you could find a way to reload the previous firmware, it would upload the new firmware when it reconnects to the network. DOCSIS modems are designed to be managed by the CMTS. The same modem might use different firmware on different networks, or even different segments of the same network. They could probably even control it by speed tier if they wanted to.

@user_94482a​   Which Arris did you have before?

Moto up to this point have had a great reputation.  I don't think they just fell off the face of the earth performance wise.

That said, this is a big boy issue that they need to resolve with Xfinity.

I just bought a Arris S33 to replace my 8611.  No problems so far 3 days on.

@user_94482a​ I'm in the same boat. Motorola MB8611 modem and Netgear Orbi RBR850 WiFi router purchased last March to take advantage of the new speed tier. Worked perfectly until about a month ago. No major changes to anything on my network. Comcast technician came out and validated all the connections. I think it is highly unlikely that this is an issue with LAN side equipment. I'm very confident that you'll be able to experience the issue with a computer connected directly to the modem to rule out the router. I couldn't continue to deal with the frequent disconnects, so I ended up getting a Netgear CM2000 modem thinking it might at least rule out future incompatibility. It's been rock solid for 4 days, but no faster than the MB8611.