Odd 10Mbit cap on upstream

Ok here is the weirdness. I have 350/35 service and until last week things worked flawlessly.
Now my upstream is limited to 10Mbit exactly. If I reboot the modem I get full speed for 10 minutes exactly **IF** I run the circuit hard then back to the cap.

I've tested and the latency appears on the first comcast hop, not on my internal network and not to the modem itself (Static IPs, routed modem).

I've plugged a test Linux box into the modem and can stream up to a test server of mine at 30Mbit for exactly 10 Minutes then get clamped.
If I back off and let the circuit set idle for an hour it returns to 10 Minutes of speed again. Weird!

I'm sure this is some packet/rate limiter but haven't made any headways with support. Signal strength looks good, no obvious RF issues.

Tried plugging the modem directly into the comcast drop outside, same issue.

Suggestions?

Responses

smoats

New Contributor

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28 Messages

3 years ago

Attached is a graph showing the behavior. Weird hard cap...

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CC_Alisha

Contributor

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20 Messages

3 years ago

Hi, there! Thank you for reaching out to our Comcast Business Support Forum page. This is very odd! I would like to take a closer look and see what is causing this. Please send us a direct message with your full name, business name, and service address to get started.

To send a Direct Message:

Ensure you are logged in

Click the "Direct Messaging" icon or https://comca.st/3dZ6vQ4

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 Support" from that list.

- An "Comcast Support" graphic replaces the "To:" line.

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

Press Enter to send it

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smoats

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28 Messages

@Comcast_Alisha
Thank you, I've reach out to the comcast business (Couldn't see a support) and to your account directly.

Sam

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3 years ago

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jval

New Contributor

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9 Messages

3 years ago

I have the same service and am experiencing the exact same thing. I can get 30Mbps upload right after I reboot my modem... but 10 minutes later (and from there on out) I'm capped at 10Mbps upload.

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CC_Anna

New problem solver

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39 Messages

Thank you for reaching out @jval. I am sorry to hear you have been experiencing an upload problem. I can certainly understand how this has caused you and your business a tremendous headache. Let’s take a look together and get to the bottom of this. Can you send us a direct message to “Comcast Business” as outlined above? We look forward to hearing from you!

I no longer work for Comcast.

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3 years ago

jval

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9 Messages

Will do. Thank you.

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3 years ago

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smoats

New Contributor

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28 Messages

3 years ago

So far zero luck in resolving it here and I've tested with a friend in Stephen City (a town about 10 miles from me) who also has comcast business the same thing is happening with her modem.

This is weird and I'm sure it's a hard limit inside of the modem. Pinging the external static IP of the modem from the inside ethernet goes up to 50-100ms when under 10mbit load but externally I can ping the static IP in 20ms. The latency is inserted inside of the modem, not on the Comcast external wire. The data rate is exactly 10Mbit up, an RF issue wouldn't likely produce such a consistent round number.

Did a firmware update or something go out for these?

Sam

(edited)

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chris_hs

New Contributor

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2 Messages

3 years ago

I believe we are experiencing the same issue. The problem started on Dec. 14 after our modem rebooted at 3:07 AM for what I assume was a firmware upgrade. We have a static IP and 300/30 service.

I have sent a DM to "Comcast Business" per the instructions.

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smoats

New Contributor

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28 Messages

@chris_hs

We're also on 300/30 service and have static IPs. I'm thinking this was a bad firmware update.

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3 years ago

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chris_hs

New Contributor

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2 Messages

@smoats What type of modem do you have?

A tech was out this morning. He replaced our existing modem (Technicolor DPC3941B aka Business Wireless Gateway) with a new CBR-T (CGA4131COM) modem. It seems to have fixed the problem - it's been holding steady at ~35Mbps upload for over an hour now.

(edited)

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3 years ago

jval

New Contributor

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9 Messages

@chris_hs They replaced my DPC3941B with a CGA4131COM this morning as all the other checklist items (signal, connections, etc.) checked out. So far, holding steady at 35Mbps during the last 2.5hrs. I'm hopeful that this is fixed for me too!

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3 years ago

jval

New Contributor

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9 Messages

3 years ago

I'm still working through the support process. We've rebooted the modem a few times. I've removed the 4-way splitter and and the coax is now going directly into the back of the modem. Still measuring 350Mbps down and somewhere between 9Mbps and 10Mbps up.

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Comcast_William

Official Employee

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26 Messages

Good morning @jval. Please send another direct message and we can get to the bottom of this speed issue for you. We look forward to hearing from you!

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3 years ago

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smoats

New Contributor

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28 Messages

Jval if you can try disabling flow control on your switch ethernet port. Not saying this is the issue but after an unexpected reboot of my modem things seem to be working properly here. The only change I see is flow control is now autodetected as off by my switch.

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3 years ago

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smoats

New Contributor

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28 Messages

@jval Spoke to soon, back to 10Mbit up. Oddly just unplugging and reconnecting the ethernet wire gets me back to full speed for about 10 minutes. Weird.

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3 years ago

jval

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9 Messages

Exact same behavior! I just checked and it was 9Mbps upload - so based on your recommendation I disabled/reenabled the switch port and am also full-speed upload again (for now). I've disabled flow-control on that interface as well and I'll monitor to see how long it takes before dropping below 10Mbps again.

So far, 30 minutes after unplugging, disabling flow-control on the switchport connected to my comcast modem, and plugging back in, and it's still 35Mbps upload... so somewhat encouraging. I'll keep testing throughout the day.

(edited)

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3 years ago

jval

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9 Messages

@Comcast_William I responded to @comcast_business via direct message earlier this morning with a status update but haven't heard back yet.

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3 years ago

smoats

New Contributor

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28 Messages

3 years ago

We'll have some time tomorrow, I'm going to call into the enterprise help desk and see if they'll let me swap modem types without having to schedule a truck roll. I'm fairly confident that'll fix it, the hard part is going to be getting tech to agree.

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jval

New Contributor

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9 Messages

@smoats I bought a Netgear modem not too long ago, but can't implement it while also keeping static IP addresses. :/ I'll ask for a truck roll.

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3 years ago

jval

New Contributor

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9 Messages

3 years ago

Had a visit from a field technician today. About 30 minutes before he arrived, upload speeds were 35Mbps. The troubleshooting gods were with me this morning as the first speedtest I showed him was a 9Mbps test. He hadn't heard of similar symptoms, but proceeded to check all of the basics. Physical connections, signal quality, wired vs wireless, dmarc box, pedestal, etc. He ended up swapping out my modem for a new(er) DOCSIS 3.1 model. So far it's been an hour with 35Mbps uploads. Keeping the fingers crossed that it stays that way!

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CC_Kyla

Contributor

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7 Messages

I'm happy to hear that! We're online 24/7 should you have any other questions or concerns. I hope you enjoy the rest of your day!

I no longer work for Comcast.

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3 years ago

jval

New Contributor

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9 Messages

3 years ago

A day and a half since replacing my modem and it’s still humming along at 35Mbps upload.

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CC_Anna

New problem solver

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39 Messages

That is awesome @jval. We have a wonderful group of knowledgeable technicians. It really sounds like he did a thorough job. We are certainly grateful to have patient understanding customers such as yourself. Did you have any further questions or concerns publicly for our team?

I no longer work for Comcast.

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3 years ago

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