T3 timeouts? Combo Modem/Router with router turned off.

Edmunds1
Edmunds1 Member Posts: 2
First Comment Photogenic
edited December 2020 in Devices & Security
Hi all!
I have a small house (1000sqft) that seems to have always had either wi-fi issues or connection drops over the past few years, even with 2 different ISPs.  It has gotten better but still seems to be occuring annoyingly enough.  I was using a modem/router combo: Motorola MG7700 24x8, but receently put it into Bridge Mode and linked up a Google Mesh network that seems more stable, but I get some errors popup that when I search, I get a bunch of different results.  Ive searched some of the forum and didnt come up with anything concrete, so i apologize if this is super common, but if anyone wants to look through, any insight would help!  The following is AFTER I put the combo into bridge mode with google, log from the modem itself:

The T3 time-out seems to be the one near the drops I get.  The first address is the modem itself,00:40:36:5d:a0:70, but i don't recognize the other device and dont see it in Fing (MAC lookup says it's a router though, doesnt match the router ID in my admin page.)  I am wonder if maybe the router is still acting up somehow, even in bridge mode?  One thing to note is that i still had these T3 issues even before using a second router.


 Tue Dec 01 02:43:45 2020   Error (4)  DHCP RENEW WARNING - Field invalid in response v4 option;CM-MAC=00:40:36:5d:a0:70;CMTS-MAC=00:01:5c:6a:58:57;CM-QOS=1.1;CM-VER=3.0; 
 Wed Dec 02 11:35:40 2020   Critical (3)  Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=00:40:36:5d:a0:70;CMTS-MAC=00:01:5c:6a:58:57;CM-QOS=1.1;CM-VER=3.0; 
 Sun Dec 13 01:14:12 2020   Error (4)  DHCP RENEW WARNING - Field invalid in response v4 option;CM-MAC=00:40:36:5d:a0:70;CMTS-MAC=00:01:5c:6a:58:57;CM-QOS=1.1;CM-VER=3.0; 
 Sun Dec 13 15:08:53 2020   Critical (3)  Started Unicast Maintenance Ranging - No Response received - T3 time-out;CM-MAC=00:40:36:5d:a0:70;CMTS-MAC=00:01:5c:6a:58:57;CM-QOS=1.1;CM-VER=3.0; 
 Wed Dec 16 01:14:12 2020   Error (4)  DHCP RENEW WARNING - Field invalid in response v4 option;CM-MAC=00:40:36:5d:a0:70;CMTS-MAC=00:01:5c:6a:58:57;CM-QOS=1.1;CM-VER=3.0; 
 Wed Dec 16 07:51:12 2020   Warning (5)  TEK Invalid - Invalid Key Sequence Number;CM-MAC=00:40:36:5d:a0:70;CMTS-MAC=00:01:5c:6a:58:57;CM-QOS=1.1;CM-VER=3.0; 





Best Answers

  • BK303
    BK303 Member Posts: 23
    10 Comments Name Dropper 5 Likes First Anniversary
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    Accepted Answer
    The log you are looking at is listing events on the DOCSIS interface between your cable modem and the cable company's upstream "headend" CMTS (Cable Modem Termination System).  The T3 timeouts are related to loss of synchronization of your modem to the network signals, and the "critical" issues will temporarily disrupt your network connection to your cable provider ISP.   The "DHCP renew warning" and "TEK Invalid" log entries can probably be ignored and should not disrupt service.    If a modem loss of network connection issue lasts more than a few minutes, the event will also be logged by local Fingbox monitoring (if you have a Fingbox) as Internet outages (in Fing App > Your Fingbox Network > tab "Internet" > "history").   

    The CMTS MAC is removed by the layer 2 bridging function of the cable modem and then your cable modem's MAC is also removed in your home NAT Router's layer 3 routing functions, so neither MAC address is directly visible to a Fing scan or Fingbox on your home network downstream of your home NAT Router.  As you already know, a single box can provide both the Cable Modem with bridging function as well as the home NAT Router function, but many of us like to separate the two and operate our Cable Modem in bridging mode so that we can connect our own home NAT Router, often with built-in Wifi AP or with more features than the ISP's combination modem/router/wifi box (although I'll admit Comcast's new Xfi gateway combo modem/router/wifi is exceptionally feature rich).

    In my experience, infrequent (maybe once every two weeks) loss of sync events in the cable modem log, which frequently recover within a few 10s of seconds and thus not logged by Fingbox, are typical with cable modem service.  However, daily or multiple per day modem loss of sync (T3 timeout or other "Critical") events is a real problem.   You often won't know how long a network outage lasted from just the modem logs as they show the loss sync event, but typically don't have a log entry when sync was re-established.  So I rely on my Finbox Internet monitoring history to correlate timing of longer outages to the modem logs to know if my Internet connection went out due to modem/cable network problem or if my home router or Wifi locked up and rebooted.  Frequent or longer duration cable network signal/sync problems can be caused by excessive signal losses or intermittent connections on the cabling to your modem (outside and/or inside your house), or (if nothing changed in your house lately) by new excessive "ingress" noise in your neighborhood reaching your modem and interfering with the reception of downstream signals or corrupting upstream signals at the CMTS.   

    The easiest way to check for cable network-side signal issues is to find the web page that shows the modem's "signal status" (often at 192.168.100.1 for home cable modems, or likely found in the management pages near where you found that modem log).  The downstream SNR is the most important figure of merit, and the signal levels should be within the ranges specified by the cable modem manufacturer (link to example info).  In my experience, greater than 36 dB SNR downstream yields pretty stable and good performance.  SNR below 33 dB or growing downstream "Uncorrectable Error" counts are a sign of problems that should be fixed.   I've gone through multiple rounds of degraded signal quality in my neighborhood, and they are often cleared up a few weeks after my complaints and sometimes a require technician visit to check signal quality at the entry to my house, which often are "at the limit, but acceptable".   You can troubleshoot that your house wiring is not causing the problem by moving your cable modem connection as close to where the coax wire enters your house as possible and removing any splitters.  You should very roughly expect 6 to 8 dB of loss (meaning lower, more negative received signal strength reading in dBmV) within your house (3 to 4 dB per two-way splitter and another 3 to 5 dB for inside cable length) which will be visible in as changes to the downstream signal level between different connection locations.  If your house wiring is good, you should not see much downstream SNR change (even though the signal level is lower) when comparing the normal modem location after a splitter and the best possible direct connection very close to cable entry.  If you still have frequent sync dropouts or poor SNR or low signal level (more negative than roughly -6 dBmV) with the most direct modem connection, then give your cable company a call and ask them to test your signal quality.  

    Hope this is helpful,
    B
    Edmunds1
  • Edmunds1
    Edmunds1 Member Posts: 2
    First Comment Photogenic
    edited December 2020 Accepted Answer
    Thank you for this great response!
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