Motorola MB8611 - Forensic Explanation for Xfinity Support

Forensic Explanation for Xfinity Support

Issue Summary:

After upgrading my service tier from 1 Gbps to 2 Gbps, my Motorola MB8611 received a new DOCSIS provisioning file that the modem cannot properly negotiate. Since that upgrade attempt, the modem is stuck in a degraded DOCSIS profile and will not exceed ~500 Mbps even after downgrading back to 1 Gbps.

Technical Details:

1. The modem received an incorrect or incompatible DOCSIS config file during the 2 Gbps upgrade.

• The MB8611 cannot fully negotiate the multi gig or mid split profile that was pushed.
• As a result, the modem is not bonding all downstream channels and is not locking OFDM/OFDMA correctly.

2. The modem is now stuck in a fallback DOCSIS 3.0 profile, even after downgrading.

• OFDM downstream is not locking.
• OFDMA upstream is disabled or in partial service mode.
• Channel bonding is incomplete.
• This results in a hard throughput ceiling around 400–600 Mbps.

3. Factory resets do not fix the issue because the CMTS continues to push the same incompatible config file.

• The modem is not “broken”; it is mis provisioned.
• The fix requires a correct DOCSIS config file to be manually pushed from your side.

4. This is a known issue with the MB8611 on upgraded Xfinity plants (mid split, OFDMA activation, multi gig tiers).

• Multiple customers have reported identical symptoms after a tier change.
• Field techs have acknowledged that the MB8611 often fails to re provision correctly after a multi gig upgrade attempt.

I would have preferred knowing this information before my modem was bricked. I had to buy another one - Hitron