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user_dw9rle
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09/14/2026 4:16 PM

Xfinity only allows 35 Mbps upload, but my modem supports 800 Mbps up (plus 2.5 Gbps down). Why is Xfinity artificially capping my speeds?

As in the title. I have a modem, a Motorola MB8611, which can do 2.5 Gbps download and 800 Mbps upload. However, Xfinity says it only supports 35 Mbps, which is completely wrong, by a literal order of magnitude and then some - it literally supports over 20 times the speed Xfinity says it does, and 8 times the speeds I expect.

When I upgraded, the Broadband Facts and the representative both said I would get 100 Mbps upload (which is still just a fraction of what the modem can do), and I made sure when I bought this modem that it supported those speeds. That being the only reason to upgrade, I expected the full upload speed, but it seems Xfinity is artificially capping me because... they don't like my modem, or something? They want me to buy theirs and have decided to act in subterfuge toward that end? I don't get it. There are modems on that list with a fraction of the bandwidth of mine, and Xfinity allows those a 100 Mbps upload speed, yet mine is left in the gutter for some inexplicable reason.

I get that actual traffic, bandwidth, network behavior, etc. will change and depend on network conditions, but I expected and still expect that Xfinity at least tries to allow my hardware to do what it says it can do rather than artificially cap my speeds because they think I don't know any better. This is completely ridiculous, and completely dishonest on Xfinity's part.

Anyway, my neverending complaints with this godforsaken company aside, is there a fix? Thanks.

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12 days ago

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BruceW

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14 days ago

... Motorola MB8611 ... it literally supports over 20 times the speed Xfinity says it does ...

Manufacture's speed specs are almost always higher than the speeds Comcast/Xfinity lists. 

The 8611 is not compatible with the "enhanced" upload speeds. Follow the "See all modems" link near the bottom of https://www.xfinity.com/support/internet/customerowned, and then check the devices listed under the "Compatible modems for enhanced speeds" heading. The 8611 is not on that list. In fact no Motorola models are. AFAIK Comcast/Xfinity has never said how they determine which devices are compatible with enhanced speeds. The charts on that page are pretty much all we know.  

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BruceW

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27.7K Messages

14 days ago

... It is a hardware constraint. ...

I shoulda knowed that. Thank you EG!

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user_dw9rle

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Thanks to both you and @EG for the responses, but I'm still not convinced that there's any real basis for this claim. The link they shared just had a Redditor (one with whom I have problems already) with a couple upvotes saying it's not mid-split, with no documentation to back that up at all - and I have documentation that it does support mid-split.

According to anything I can find, mid-split is literally when the split between upstream and downstream bandwidth spectrums is set at a higher frequency than sub-split, at 85 MHz (https://kb.veexinc.com/en/knowledge/what-is-mid-split-and-high-split-docsis). And the documentation for this modem is, also, showing that it supports upstream at 5 to 85 MHz, switchable from a sub-split configuration (5 to 42 MHz) according to Motorola themselves (https://en-us.support.motorola.com/ci/fattach/get/82899680/1703008337/redirect/1/filename/MB8611-DataSheet-21920.pdf).

So how can it not be mid-split? Looks like a fish, talks like a fish, etc., and I'm shocked that two apparently high-rated experts wouldn't think to actually address the issue with real information rather than a patronizing Google search, to be honest.

(edited)

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13 days ago

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XfinityThomasC

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Hello, @user_dw9rle happy to check your residence to see if your area network has been enhanced to carry that mid-split signal. That being said the device recommendation list provided by @BruceW are the compatible modems we have tested and know will work on our network vs your MB8611 which may not work at full capacity on our mid-split network. I can also check your current internet plan to see if it allows for higher than 35 Mbps upload.

Could you please send our team a direct message with your full name and full address? To send a direct message:

Click "Sign In" if necessary

Click the "Direct Messaging" icon

Click "Start new conversation" (pencil and paper) icon

In the "To:" line, type "Xfinity Support"

As you type, a drop-down list will appear. Select "Xfinity Support" from that list.

An "Xfinity Support" graphic will replace the "To:" line.

Type your message in the text area near the bottom of the window.

Press Enter to send it.

 

How to: https://forums.xfinity.com/conversations/guidelines/how-to-direct-messaging-within-the-forum/697ba1e570934d009185c514

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12 days ago

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