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New problem solver


14 Messages

Friday, February 17th, 2023 7:41 PM

Is comcast throttling download speed from certain IP#s?

Has anyone seen comcast biz internet greatly slowing down transfer speeds between your site and specific other sites? (Likely by IP#)

I have comcast biz internet at my main location, and have servers at two remote locations (one using AT&T, one using Centurylink). I transfer backups and other files between them. I've noticed that "download" file transfers from my two remote sites into my comcast site are slowed waaaay down, like 300K bytes/sec (i.e. about 2-3M bits/sec).  This is on a 750Mbit/s comcast service with static IPs (i.e. rated for approx. 75-100M bytes/s down), so 2Mb is like 0.3% of the rated speed.  When I route that exact same traffic over a VPN (att -> vpn -> comcast), I get much faster speeds, like ~150Mb/s (which is in line with the speed for the VPN service that I see to other sites). The AT&T service is symmetrical fiber at 500/500Mb/s, so 2Mb/s is just insanely slow.  Transfers in the other direction, "uploading" from comcast to my remote sites, goes as expected (35Mbit/s comcast service and I see just about that, ~4.5MByte/s).  When I transfer from sites that aren't my remote servers, I see the expected speeds (i.e. the max upload speed of the remote site, say, ~100Mb/s; no throttling). Speedtest sites give me the expected speeds of like ~900Mb/s down & ~42Mb/s up. (Clearly comcast is not throttling speedtest sites!)

Data transferring from my at&t 500Mb/s-up to my comcast 750Mb/s-down sites should flow at something near the 500Mb/s rate; even 100-200Mb/s would feel ok-ish. But 2Mb/s?!?

And the only difference between turtle-ish 2Mb/s and normal, zippy speed is the ip#. (And the fact that I do a lot of transfers between them on a daily basis.)

I thought it might be the remote ends doing the throttling, but that would have to be BOTH at&t and centurylink doing the same thing to my comcast ip# -- whereas the Occam's Razor simplest answer suggests it's comcast that's doing the slow down to ip#s it puts on some list. (Perhaps based on noticing traffic between them? dunno)

Anyone else seen this?

And, more importantly, any ideas how to get my ip#s unthrottled? :)

Thanks for any insights!

Official Employee


23 Messages

1 year ago

Good afternoon, @aburt! We are happy to help with the connection issues. We want your service to work great all of the time. This is great detail that you provided in your post. Nothing is sticking out so far as the root cause. We do not throttle, so there is definitely an issue happening that we need to get fixed. We will need to access the account to investage this further. Please send us a direct chat message with your first and last name, the service address, and the account number. To send a direct chat message to "Comcast Business": 
Here's the detailed steps to direct message us:
Click "Sign In" if necessary 
Click the "Direct Messaging" icon or go to
Click the "New message" (pencil and paper) icon 
The "To:" line prompts you to "Type the name of a person". Instead, type "Comcast Business" there 
- As you are typing a drop-down list appears. Select "Comcast Business" from that list 
- A "Comcast Business" graphic replaces the "To:" line 
Type your message in the text area near the bottom of the window 
Press Enter to send it"