Internet connection drops every day at the same time

[mwest1705]

This problem has been going on for over a week. Every day at around noon, my cable modem (C6300v2) disconnects from the internet. It will stay disconnected for anywhere from one minute to an hour and keeps disconnecting/reconnecting throughout the afternoon until early evening when the connection finally stabilizes and then it's fine until the next day when it starts all over again. This has happened with two different, and brand-new, Netgear cable modems/router. I've had technicians from my ISP (Xfinity) visit twice and they insist there is nothing wrong with the line from them.  I've been on phone tech support with Netgear every day for the last 6 days and nothing they've suggested (including returning the first router and getting a diffferent one) has worked. Here's what I know so far:

1 - Restarting the modem/router does not re-establish the connection. Factory resets have had no effect.

2 - The Event logs are full of error messages that occur at the time of the disconnection. They are:

No Ranging Response received - T3 time-out
Received Response to Broadcast Maintenance Request, But no Unicast Maintenance opportunities received - T4 time out
Started Unicast Maintenance Ranging - No Response received - T3 time-out
Unicast Ranging Received Abort Response - initializing MAC
B-INIT-RNG Failure - Retries exceeded

Those all occur repeatedly until the connection finally stabilizes.

3- The first error messages that appears in the Event Log at the time of the first disconnecction is multiple Time Synchronization failures. Neither of these cable modems has ever had the correct system time. They're both one hour off and I can't seem to find any way to set the time manually. My understanding is that the time is supposed to be set by the ISP, but that doesn't seem to be happening.

4 - The Event logs also have a lot of DoS attack warnings, like:

[DoS attack] ICMP Flood from fe80:0000:0000:0000:1a8b:9dff:fed4:0822

5- The cable modem/router is connected directly into the wall Coax cable. There are no line-splitters attached, inside the house anyway.

6- Wireless connectivity to the router/modem is never disrupted, just the internet connection.

7- The firmware is up-to-date (1.03.06). I'm on a Windows 10 PC.

Xfinity/Comcast believes the fault is with the modem/router. Netgear phone tech support has essentially given up. Does anyone have any idea what could possibly be causing this? I'm stumped as to what to do next and obviously this situation is not acceptable.

[mwest1705 · Accepted solution]

Well, Comcast finally came and replaced all the cables from the house to the street and that seems to have done the trick.  I suspect, but don't know for sure, that the problem was with the upstream which I don't think they were testing the first two times they came out.

[Larry101]

I had a problem too, but I only had the modem, Netgear CM1100, Cox said replace the modem and I had no problem since. I've read somewhere that "*they*" suggest to turn off the router function and use a separate router.

[mwest1705]

Hmm. It's an idea, but I'm not sure I want to buy a third router. Maybe I should have got a separate modem and router to start with, though.
I can't help but think that if I knew what was causing it, I could fix it. Something is happening at noon that's triggering this, but I can't figure out what it is.

[Larry101]

Coincident?? I had a CM1100-->MK63 two months ago. My satellites disconnected about the same time 7pm PDT every day. There were a lot of problem with this MK63 mesh, so I returned after two weeks and bought a compatible TP-Link system. It worked great since then.

[mwest1705 · Accepted solution]

Well, Comcast finally came and replaced all the cables from the house to the street and that seems to have done the trick.  I suspect, but don't know for sure, that the problem was with the upstream which I don't think they were testing the first two times they came out.