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Netgear AC1900 C7000v2 Downstream Light Flashing
I have had the same provider (Xfinity) and the same modem router for about 14 months.
I had never had this problem before, but starting last week somewhere around 5 times a day the downstream light will start blinking, and the wifi will go down. This blinking will last a couple minutes, then the wifi will still be down for a minute or so after the light goes back to solid. Sometimes this will happen a few times an hour and sometimes it will be perfectly fine for 6 hours.
I have tried reconnecting the coax as well as power cycling a few times but the problem still persists. Does anyone have any ideas on what the issue could possibly be? I have used Xfinity's online wizard which always assures me nothing is wrong, and I could call a tech but would like to be more confident that the problem is actually on the ISP side before potentially having to pay for a tech to come out.
Any ideas / recommendations are welcome!
Power levels are too high. https://kb.netgear.com/24311/Power-level-guidelines-for-a-NETGEAR-cable-modem-router
Get you a -6dbm coax cable line attenuator between the modem and coax line.
Got some correctables and un-correctables however not horrible. Should be mostly zeros.
Have the ISP check the signal and line quality UP to the modem. Be sure the ISP provisions the modem correctly.
Be sure there are no coax cable line splitters in the between the modem and ISP service box.
Be sure your using good quality RG6 coax cable up to the modem.
Start with removing any amplifiers, signal attenuators, or splitters from the coax.
From there check the line for kinks, damage, moisture in the line.
Check the connectors for improperly made ends, foil touching the copper coax line, loose connections, bad/old/cheap connectors, or corroded connections. Replace them if you do.
Be sure to power OFF the modem for 1 minute then back ON.
https://community.netgear.com/t5/Cable-Modems-Routers/General-info-and-Troubleshooting-for-Cable-Modems/m-p/1530376#M12853https://www.duckware.com/tech/solving-intermittent-cable-modem-issues.html
https://highspeed.tips/docsis-events/
11 Replies
2025-8-25, 13:57:20 Critical (3) Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=54:07:7d:ba:ac:0e;CMTS-MAC=00:01:5c:a7:5a:7b;CM-QOS=1.1;CM-VER=3.0; 2025-8-25, 13:57:20 Warning (5) MDD message timeout;CM-MAC=54:07:7d:ba:ac:0e;CMTS-MAC=00:01:5c:a7:5a:7b;CM-QOS=1.1;CM-VER=3.0; 2025-8-25, 13:57:20 Critical (3) Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out;CM-MAC=54:07:7d:ba:ac:0e;CMTS-MAC=00:01:5c:a7:5a:7b;CM-QOS=1.1;CM-VER=3.0; 2025-8-25, 13:57:20 Warning (5) MDD message timeout;CM-MAC=54:07:7d:ba:ac:0e;CMTS-MAC=00:01:5c:a7:5a:7b;CM-QOS=1.1;CM-VER=3.0; 2025-8-25, 13:52:30 Critical (3) Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=54:07:7d:ba:ac:0e;CMTS-MAC=00:01:5c:a7:5a:7b;CM-QOS=1.1;CM-VER=3.0; 2025-8-25, 13:52:30 Warning (5) MDD message timeout;CM-MAC=54:07:7d:ba:ac:0e;CMTS-MAC=00:01:5c:a7:5a:7b;CM-QOS=1.1;CM-VER=3.0; 2025-8-25, 13:51:03 Critical (3) Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=54:07:7d:ba:ac:0e;CMTS-MAC=00:01:5c:a7:5a:7b;CM-QOS=1.1;CM-VER=3.0; 2025-8-25, 13:51:03 Warning (5) MDD message timeout;CM-MAC=54:07:7d:ba:ac:0e;CMTS-MAC=00:01:5c:a7:5a:7b;CM-QOS=1.1;CM-VER=3.0; 2025-8-25, 12:58:52 Critical (3) Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=54:07:7d:ba:ac:0e;CMTS-MAC=00:01:5c:a7:5a:7b;CM-QOS=1.1;CM-VER=3.0; 2025-8-25, 12:58:52 Warning (5) MDD message timeout;CM-MAC=54:07:7d:ba:ac:0e;CMTS-MAC=00:01:5c:a7:5a:7b;CM-QOS=1.1;CM-VER=3.0; 2025-8-25, 12:58:52 Critical (3) Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out;CM-MAC=54:07:7d:ba:ac:0e;CMTS-MAC=00:01:5c:a7:5a:7b;CM-QOS=1.1;CM-VER=3.0; 2025-8-25, 12:58:51 Warning (5) MDD message timeout;CM-MAC=54:07:7d:ba:ac:0e;CMTS-MAC=00:01:5c:a7:5a:7b;CM-QOS=1.1;CM-VER=3.0; 2025-8-25, 12:42:05 Critical (3) Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=54:07:7d:ba:ac:0e;CMTS-MAC=00:01:5c:a7:5a:7b;CM-QOS=1.1;CM-VER=3.0; 2025-8-25, 12:42:05 Warning (5) MDD message timeout;CM-MAC=54:07:7d:ba:ac:0e;CMTS-MAC=00:01:5c:a7:5a:7b;CM-QOS=1.1;CM-VER=3.0; 2025-8-25, 12:40:57 Critical (3) Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=54:07:7d:ba:ac:0e;CMTS-MAC=00:01:5c:a7:5a:7b;CM-QOS=1.1;CM-VER=3.0; 2025-8-25, 12:40:57 Warning (5) MDD message timeout;CM-MAC=54:07:7d:ba:ac:0e;CMTS-MAC=00:01:5c:a7:5a:7b;CM-QOS=1.1;CM-VER=3.0; 2025-8-25, 12:29:19 Critical (3) Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=54:07:7d:ba:ac:0e;CMTS-MAC=00:01:5c:a7:5a:7b;CM-QOS=1.1;CM-VER=3.0; 2025-8-25, 12:29:19 Warning (5) MDD message timeout;CM-MAC=54:07:7d:ba:ac:0e;CMTS-MAC=00:01:5c:a7:5a:7b;CM-QOS=1.1;CM-VER=3.0; 2025-8-25, 11:26:44 Critical (3) Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=54:07:7d:ba:ac:0e;CMTS-MAC=00:01:5c:a7:5a:7b;CM-QOS=1.1;CM-VER=3.0; 2025-8-25, 11:26:43 Warning (5) MDD message timeout;CM-MAC=54:07:7d:ba:ac:0e;CMTS-MAC=00:01:5c:a7:5a:7b;CM-QOS=1.1;CM-VER=3.0; 2025-8-25, 10:20:49 Critical (3) Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=54:07:7d:ba:ac:0e;CMTS-MAC=00:01:5c:a7:5a:7b;CM-QOS=1.1;CM-VER=3.0; 2025-8-25, 10:20:49 Warning (5) MDD message timeout;CM-MAC=54:07:7d:ba:ac:0e;CMTS-MAC=00:01:5c:a7:5a:7b;CM-QOS=1.1;CM-VER=3.0; 2025-8-25, 10:20:49 Critical (3) Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out;CM-MAC=54:07:7d:ba:ac:0e;CMTS-MAC=00:01:5c:a7:5a:7b;CM-QOS=1.1;CM-VER=3.0; 2025-8-25, 10:20:49 Warning (5) MDD message timeout;CM-MAC=54:07:7d:ba:ac:0e;CMTS-MAC=00:01:5c:a7:5a:7b;CM-QOS=1.1;CM-VER=3.0; 2025-8-25, 10:13:11 Critical (3) Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=54:07:7d:ba:ac:0e;CMTS-MAC=00:01:5c:a7:5a:7b;CM-QOS=1.1;CM-VER=3.0; 2025-8-25, 10:13:11 Critical (3) Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out;CM-MAC=54:07:7d:ba:ac:0e;CMTS-MAC=00:01:5c:a7:5a:7b;CM-QOS=1.1;CM-VER=3.0; 2025-8-25, 10:13:11 Warning (5) MDD message timeout;CM-MAC=54:07:7d:ba:ac:0e;CMTS-MAC=00:01:5c:a7:5a:7b;CM-QOS=1.1;CM-VER=3.0; 2025-8-25, 09:11:49 Critical (3) Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=54:07:7d:ba:ac:0e;CMTS-MAC=00:01:5c:a7:5a:7b;CM-QOS=1.1;CM-VER=3.0; 2025-8-25, 09:11:49 Warning (5) MDD message timeout;CM-MAC=54:07:7d:ba:ac:0e;CMTS-MAC=00:01:5c:a7:5a:7b;CM-QOS=1.1;CM-VER=3.0; 2025-8-25, 09:11:49 Critical (3) Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out;CM-MAC=54:07:7d:ba:ac:0e;CMTS-MAC=00:01:5c:a7:5a:7b;CM-QOS=1.1;CM-VER=3.0; 2025-8-25, 09:11:49 Warning (5) MDD message timeout;CM-MAC=54:07:7d:ba:ac:0e;CMTS-MAC=00:01:5c:a7:5a:7b;CM-QOS=1.1;CM-VER=3.0; 2025-8-25, 08:08:20 Critical (3) Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=54:07:7d:ba:ac:0e;CMTS-MAC=00:01:5c:a7:5a:7b;CM-QOS=1.1;CM-VER=3.0; 2025-8-25, 08:08:20 Warning (5) MDD message timeout;CM-MAC=54:07:7d:ba:ac:0e;CMTS-MAC=00:01:5c:a7:5a:7b;CM-QOS=1.1;CM-VER=3.0; These timestamps found in the event log seem to correlate with the outages, but I am not familiar enough with networking to understand what they mean. Assuming this is the key here, based on other approaches it seems the solution is to troubleshoot with ISP but the tech won't know much about it. Is that understanding correct?
Please post a copy and paste of the modems connection status log page.
https://kb.netgear.com/30007/How-do-I-obtain-the-cable-connection-information-from-a-NETGEAR-cable-modem-modem-routerAny Criticals, Errors or Warnings seen in the event logs needs to be reviewed and resolved by the ISP. Indicates a signal issue on the ISP line up to the modem.
- status log page below, thanks for the help
Procedure
Status Comment Acquire Downstream Channel 585000000 Hz Locked Connectivity State OK Operational Boot State OK Operational Security Enabled BPI+ IP Provisioning Mode Honor MDD honorMdd(4) Downstream Bonded Channels Channel Lock Status Modulation Channel ID Frequency Power SNR Correctables Uncorrectables 1 Locked QAM256 24 585000000 Hz 9.8 dBmV 40.2 dB 11 0 2 Locked QAM256 25 591000000 Hz 9.7 dBmV 39.9 dB 9 0 3 Locked QAM256 26 597000000 Hz 9.9 dBmV 40 dB 26 0 4 Locked QAM256 27 603000000 Hz 10 dBmV 40.2 dB 17 0 5 Locked QAM256 28 609000000 Hz 10 dBmV 39.9 dB 17 0 6 Locked QAM256 29 615000000 Hz 10.1 dBmV 40.2 dB 1 0 7 Locked QAM256 30 621000000 Hz 10.2 dBmV 40.1 dB 2 0 8 Locked QAM256 31 627000000 Hz 10.5 dBmV 40.4 dB 42 0 9 Locked QAM256 32 633000000 Hz 10.7 dBmV 40.6 dB 27 0 10 Locked QAM256 33 639000000 Hz 11 dBmV 40.3 dB 26 29 11 Locked QAM256 34 645000000 Hz 11.1 dBmV 41 dB 39 0 12 Locked QAM256 35 651000000 Hz 10.9 dBmV 40.6 dB 9 0 13 Locked QAM256 36 657000000 Hz 10.5 dBmV 40.3 dB 19 0 14 Locked QAM256 37 663000000 Hz 10.4 dBmV 40.3 dB 8 0 15 Locked QAM256 38 669000000 Hz 10.4 dBmV 40.1 dB 25 0 16 Locked QAM256 39 675000000 Hz 10.2 dBmV 39.6 dB 7 0 17 Locked QAM256 40 681000000 Hz 9.2 dBmV 39.9 dB 0 0 18 Locked QAM256 41 687000000 Hz 9.6 dBmV 40.5 dB 0 0 19 Locked QAM256 42 693000000 Hz 10 dBmV 40.9 dB 0 0 20 Locked QAM256 43 699000000 Hz 10.7 dBmV 40.8 dB 0 0 21 Locked QAM256 44 705000000 Hz 10.7 dBmV 41.3 dB 0 0 22 Locked QAM256 45 711000000 Hz 10.4 dBmV 41.4 dB 0 0 23 Locked QAM256 46 717000000 Hz 9.8 dBmV 40.8 dB 0 0 24 Locked QAM256 47 723000000 Hz 9.4 dBmV 40.3 dB 0 0 Upstream Bonded Channels Channel Lock Status US Channel Type Channel ID Symbol Rate Frequency Power 1 Locked ATDMA 4 5120 Ksym/sec 29200000 Hz 40.5 dBmV 2 Locked ATDMA 1 2560 Ksym/sec 10400000 Hz 38.5 dBmV 3 Locked ATDMA 2 5120 Ksym/sec 16400000 Hz 39.6 dBmV 4 Locked ATDMA 3 5120 Ksym/sec 22800000 Hz 40 dBmV 5 Locked ATDMA 5 5120 Ksym/sec 35600000 Hz 41.1 dBmV 6 Locked ATDMA 6 2560 Ksym/sec 40400000 Hz 41 dBmV 7 Not Locked Unknown 0 0 Ksym/sec 0 Hz 0.0 dBmV 8 Not Locked Unknown 0 0 Ksym/sec 0 Hz 0.0 dBmV Power levels are too high. https://kb.netgear.com/24311/Power-level-guidelines-for-a-NETGEAR-cable-modem-router
Get you a -6dbm coax cable line attenuator between the modem and coax line.
Got some correctables and un-correctables however not horrible. Should be mostly zeros.
Have the ISP check the signal and line quality UP to the modem. Be sure the ISP provisions the modem correctly.
Be sure there are no coax cable line splitters in the between the modem and ISP service box.
Be sure your using good quality RG6 coax cable up to the modem.
Start with removing any amplifiers, signal attenuators, or splitters from the coax.
From there check the line for kinks, damage, moisture in the line.
Check the connectors for improperly made ends, foil touching the copper coax line, loose connections, bad/old/cheap connectors, or corroded connections. Replace them if you do.
Be sure to power OFF the modem for 1 minute then back ON.
https://community.netgear.com/t5/Cable-Modems-Routers/General-info-and-Troubleshooting-for-Cable-Modems/m-p/1530376#M12853https://www.duckware.com/tech/solving-intermittent-cable-modem-issues.html
https://highspeed.tips/docsis-events/
Thanks for your help, I have ordered a new cable just to see if that changes anything. If not, will go forward with ISP and the attenuator.
Typical aerial cable coax lines often develop "issues" over time that lead to intermittent connections. There have been a number of posts on the Forum describing how the cable tech replaced the entire cable feed.
My experience is that cable techs carry power level meters and an assortment of attenuators. My Spectrum tech remarked, "oh. level too high" and installed one. (free)
Thanks for the help CrimpOn and FURRYe38 , going to buy something like this https://www.amazon.com/6db-Attenuator-Pad-1-each/dp/B0013L48XA and will let you know how it goes
Just closing the loop here, a tech came and said while I was missing a filter, the signal looked fine on their end. They installed a splitter (-3.5db) and a filter. He does not think this was the major cause, and blamed it on the firmware / hardware of the router. Nonetheless, they still covered the cost so no complaints on my end. I have not had internet issues since they came out (Friday August 29) and my signal table seems much more stable based on the links you sent above (all powers below 7dB, 0 uncorrectables and way less correctables).
Thanks for all your help CrimpOn FURRYe38 , this is hopefully resolved!New signal info:
Downstream Bonded Channels Channel Lock Status Modulation Channel ID Frequency Power SNR Correctables Uncorrectables 1 Locked QAM256 44 705000000 Hz 7 dBmV 41.4 dB 0 0 2 Locked QAM256 24 585000000 Hz 5.6 dBmV 40.9 dB 0 0 3 Locked QAM256 25 591000000 Hz 5.5 dBmV 40.2 dB 0 0 4 Locked QAM256 26 597000000 Hz 5.6 dBmV 40.3 dB 2 0 5 Locked QAM256 27 603000000 Hz 5.7 dBmV 40.5 dB 0 0 6 Locked QAM256 28 609000000 Hz 5.7 dBmV 40.1 dB 0 0 7 Locked QAM256 29 615000000 Hz 5.8 dBmV 40.7 dB 0 0 8 Locked QAM256 30 621000000 Hz 5.9 dBmV 40.4 dB 1 0 9 Locked QAM256 31 627000000 Hz 6.2 dBmV 41 dB 0 0 10 Locked QAM256 32 633000000 Hz 6.4 dBmV 41.3 dB 2 0 11 Locked QAM256 33 639000000 Hz 6.6 dBmV 40.8 dB 0 0 12 Locked QAM256 34 645000000 Hz 6.7 dBmV 41.6 dB 0 0 13 Locked QAM256 35 651000000 Hz 6.6 dBmV 41.2 dB 0 0 14 Locked QAM256 36 657000000 Hz 6.1 dBmV 40.8 dB 1 0 15 Locked QAM256 37 663000000 Hz 6 dBmV 40.8 dB 0 0 16 Locked QAM256 38 669000000 Hz 6 dBmV 40.2 dB 1 0 17 Locked QAM256 39 675000000 Hz 4.8 dBmV 40.6 dB 0 0 18 Locked QAM256 40 681000000 Hz 4.8 dBmV 40.3 dB 0 0 19 Locked QAM256 41 687000000 Hz 5.2 dBmV 40.8 dB 0 0 20 Locked QAM256 42 693000000 Hz 5.6 dBmV 41.4 dB 0 0 21 Locked QAM256 43 699000000 Hz 6.1 dBmV 41.4 dB 0 0 22 Locked QAM256 45 711000000 Hz 5.8 dBmV 41.5 dB 0 0 23 Locked QAM256 46 717000000 Hz 5.2 dBmV 41.3 dB 0 0 24 Locked QAM256 47 723000000 Hz 4.8 dBmV 40.8 dB 0 0 Upstream Bonded Channels Channel Lock Status US Channel Type Channel ID Symbol Rate Frequency Power 1 Locked ATDMA 3 5120 Ksym/sec 22800000 Hz 43.3 dBmV 2 Locked ATDMA 1 2560 Ksym/sec 10400000 Hz 41.8 dBmV 3 Locked ATDMA 2 5120 Ksym/sec 16400000 Hz 43 dBmV 4 Locked ATDMA 4 5120 Ksym/sec 29200000 Hz 43.8 dBmV 5 Locked ATDMA 5 5120 Ksym/sec 35600000 Hz 44.8 dBmV 6 Locked ATDMA 6 2560 Ksym/sec 40400000 Hz 44.5 dBmV 7 Not Locked Unknown 0 0 Ksym/sec 0 Hz 0.0 dBmV 8 Not Locked Unknown 0 0 Ksym/sec 0 Hz 0.0 dBmV Glad you got it working. Be sure to save off a back up configuration to file for safe keeping. Saves time if a reset is needed.
https://kb.netgear.com/24231/How-do-I-back-up-the-router-configuration-settings-on-my-Nighthawk-routerEnjoy. 📡
The following was installed.
