So I've been using Xfinity with an old Arris surfboard modem for well over a year. The plan was 800/20 (before the recent network upgrades) and I could reliably get measurements of 700-840/22-24. Earlier this year I got notified that I could get 5-10x faster uploads with a new modem.

Today I swapped in a new CM3000. I couldn't activate at the activation website nor through the app. Had to struggle to reach a human, but finally got things set up. I was really pleased my uploads are now consistently over 100 Mbps, typically 115-122. But my downloads are really inconsistent. Even on a wired computer I'm getting numbers like 280-700, but mostly towards the low end.

In the modem diagnostic log, I noticed that IP Provisioning mode is "IPv6 only". I don't know if that is important. I also see lots of errors on channels 29-32. Now I recall seeing a lot of high-channel errors in the logs from the old modem, but because the performance was great, I didn't look any deeper. But this new modem's inconsistent downloads are bugging me. I wonder if Comcast mis-configured something?

It's only been 2 hours, so it's not like I've had enough time to see poor performance outside of what the tests show. But it still seems like my downloads should be consistently fast like the uploads are.

Cable Diagnostic

Status: Good

Action:
Your setup looks fine. If you can't access the internet, make sure you properly activated the modem. If modem has been activated and you still can't access the internet, contact your service provider for troubleshooting help.
If you can access the internet but has other internet issue, the Netgear Cable Knowledge Base can provide additional troubleshooting info.

CM Status: Good

Downstream Status: Good

Downstream Power Level: Good

Downstream SNR Level: Good

Upstream Status: Good

Upstream Power Level: Good

Current Time: Sat Mar 16 12:09:06 2024

Startup Procedure
Acquire Downstream Channel: 471000000 Hz Locked
Connectivity State: OK Operational
Boot State: OK Operational
Security: Enabled BPI+
IP Provisioning Mode: Honor MDD IPv6 only

Downstream Bonded Channels
Channel LockedStatus Modulation ChannelID Frequency Power SNR Correctables Uncorrectables
1 Locked QAM256 4 471000000 Hz -6.3 41.7 3 0
2 Locked QAM256 1 453000000 Hz -6.5 41.6 3 0
3 Locked QAM256 2 459000000 Hz -6.6 41.5 4 0
4 Locked QAM256 3 465000000 Hz -6.7 41.4 4 0
5 Locked QAM256 5 477000000 Hz -6.3 41.3 9 0
6 Locked QAM256 6 483000000 Hz -6.2 41.4 3 0
7 Locked QAM256 7 489000000 Hz -5.7 42.3 3 0
8 Locked QAM256 8 495000000 Hz -6.2 41.9 4 0
9 Locked QAM256 9 501000000 Hz -6.2 41.7 11 0
10 Locked QAM256 10 507000000 Hz -6.8 41.4 9 0
11 Locked QAM256 11 513000000 Hz -7 41.1 1 0
12 Locked QAM256 12 519000000 Hz -7.1 41.1 0 0
13 Locked QAM256 13 525000000 Hz -7.4 40.9 1 0
14 Locked QAM256 14 531000000 Hz -7.1 41.2 3 0
15 Locked QAM256 15 537000000 Hz -7.4 40.9 3 0
16 Locked QAM256 16 543000000 Hz -7.1 41.2 2 0
17 Locked QAM256 17 549000000 Hz -7.2 41 0 0
18 Locked QAM256 18 555000000 Hz -8 40.3 0 0
19 Locked QAM256 19 561000000 Hz -9 39.5 0 0
20 Locked QAM256 20 567000000 Hz -8.6 39.9 0 0
21 Locked QAM256 21 573000000 Hz -8.3 39.9 0 0
22 Locked QAM256 22 579000000 Hz -8.4 40.1 0 0
23 Locked QAM256 23 585000000 Hz -8.3 40.2 0 0
24 Locked QAM256 24 591000000 Hz -8.2 40.1 0 0
25 Locked QAM256 25 597000000 Hz -7.8 40.2 0 0
26 Locked QAM256 26 603000000 Hz -8.5 39.7 0 0
27 Locked QAM256 27 609000000 Hz -9.1 39.5 0 0
28 Locked QAM256 28 615000000 Hz -8.9 39.7 0 0
29 Locked QAM256 29 621000000 Hz -8.9 35 31970 857
30 Locked QAM256 30 627000000 Hz -8.9 32.3 3149748 1998709
31 Locked QAM256 31 633000000 Hz -8.7 36 4125986 5649316
32 Locked QAM256 32 639000000 Hz -8.3 37.8 829447 1292733

Upstream Bonded Channels
Channel LockedStatus ChannelType ChannelID SymbolRate Frequency Power
1 Locked ATDMA 3 5120 Ksym/sec 29200000 Hz 51.3 dBmV
2 Locked ATDMA 2 5120 Ksym/sec 22800000 Hz 50.8 dBmV
3 Locked ATDMA 1 5120 Ksym/sec 16400000 Hz 50.3 dBmV
4 Locked ATDMA 4 5120 Ksym/sec 35600000 Hz 51.5 dBmV
5 Not Locked Unknown 0 0 0 0.0
6 Not Locked Unknown 0 0 0 0.0
7 Not Locked Unknown 0 0 0 0.0
8 Not Locked Unknown 0 0 0 0.0

Forum Discussion

XFinity w/ CM3000 - Fast uploads, but slow, inconsistent download speeds