Connection drops multiple times a day. T3 T4 time-out in modem logs

I've been having a similar issue for many weeks - I keep losing my internet connection because I can't access any  DNS servers - it happens intermittently, sometimes will be fine for a day, other times like today I'm losing DNS multiple times per hour, drives me insane. I'm using two tools to check nameserver access times, DNS Jumper and DNS Benchmark - DNS Jumper lets you change nameservers on the fly - I never used that app until last week, always used Comcast or Google DNS, so it's not the app that's causing issues.

Comcast came out 3 days ago to check the line signal, it was fine, and they replaced the modem - internet worked for a day then the same DNS problems returned, so it's not the modem and not the signal strength. I thought maybe my NIC was going bad (although I've never seen that happen in 25 yrs in 4-5 PCs) so I switched to WiFi - no joy - exact same problems - it just happened TWICE while I was writing this post! How on earth can my PC lose DNS access to every public nameserver on the NIC and the WiFi Lan Card at the same time? Seriously, this is driving me bonkers - I listen to streaming XM all day long every day so I instantly know when DNS goes down. It's almost like I have a cable connection that's failing multiple times per day - I can't think of any other reason that could cause this. Any ideas from anyone? Screenshot of DNS Jumper showing access errors is attached.

@sampathk1 what type of modem do you have?  I was having similar issues I own an ARRIS SB6141 modem.  Comcast told me to contact the modem manufacturer only to find out that my upstream levels were "out of acceptable range."  Just curious what type of modem you have to look up what the acceptable range is with yours.  I just had a tech come out today he identified there was a 3 way splitter outside degrading my signal so he removed it.  Power levels are "ok" but he did say that there was another issue in the connection in the box outside so he has to log a maintenance ticket for them to come out and fix it.  Definitely sounds like an issue on Comcast end to me.

When I told the tech I was seeing the T3 timeout messages he said that always usually indicates a problem somewhere outside with their (Comcast) equipment/setup.

I first had D-Link dcm-301 when the problem started. This is still a supported modem. Then, I got a Netgear CM500. Both are highly rated modems. Both had similar issues.

Reading these forums, folks with different Motorola and Arris modems have similar issue.  All these make me believe this is not to do with any of the client side things. I hope someone from Comcast side is reading these forums and give some sort of eyes and ears to customer complaints like these.

No corporation is going to last forever even if they are monopolising their market today. I am just hoping for FIOS one day or affordable 5G to get out of this cable nonsense. 

That (locked already!?!) thread explains what's probably going on with my terrible connection too. I also get really odd results from various speedtests (all numbers are Mbps - Xfinity's says 50 down on IPv6 which is DISABLED (test doesn't give upload speed), Google's reports 50 down and 10 up, but speedtest.com reports 297 down 12 up, speakeasy.net reports 310 down and 12 up - I have the "Internet Plan: Blast! Internet", Download Speed: 300Mbps Upload Speed: 10Mbps - so why is Xfinity and Google only reporting 50 down?

No T3 or T4 errors show up in my Technicolor modem (brand new, installed last week), no errors at all. Even installed a new NIC to see if that was the problem, nope, same disconnect issues every 2-3 mins, then online for hours, then it all starts again - see attached - DNS Jumper pings every public server, you can see I can't get to many of them, most times they all come up as not accessible. Too confuse things even more, my stock trading app uses different services than http or https to download realtime data, and it rarely goes down.

Oh, one other thing I noticed - when I got the new modem I disabled the Hotspot function, but when I went to the Xfinity network page I noticed it was re-enabled - if I decide to disable it Comcast should not be re-enabling it without my permission!

Another update - got Comcast's own modem - Gateway. Plugged in, activated and in 30 minutes same problem. In the last 15 hours or so, I had connectivity dropped at least 5 times. This validates my point of problem not within my home. It must be somewhere outside. Hope the tech who is going to visit today will have access to better tools to figure that out.

@sampathk1 sounds like a signal issue outside. Idk with their modems what power ranges are acceptable and if they even report the levels like my SB6141 does. Did the tech find anything? Mine found an issue in the box and a 3-way splitter which was degrading my signal. I forget what else was bad in the box but the tech didn't do his job and log a maintenance ticket so I another tech coming out this mornin

Nothing was done by the tech other than running some signal strenth tests and checking the cables for tightness. I showed him the logs from Gateway modem. He then spoke to his supervisor. 

All along they were saying they can't check the logs in our own modem. Now, I hear they need more samples of the logs from their modem - looks like 3 disconnects in 1 day is not enough for them!

Then a strange thing - the tech wanted me to cancel the appointement! I can guess for what reason but not going to speculate here. Supervisor spoke to me and said he is going to review the logs from the neighbourhood for similar issues. Did not hear any update from him since then. But, it has been 2.5 days without any disconnects... can't believe that. I have seen upto 2 days going without issues in the past. So, will wait for one full working week before I say this is now resolved.

What state are you in? I was away for the weekend, just turned my network monitor back on, and for the last hour zero connection drops - I'm in MD. Wonder if Comcast is reading this thread and fixing issues according to our nicks? BTW, the monitor I'm using (besides DNS Jumper) is an extension for Google Chrome:

https://chrome.google.com/webstore/detail/internet-connection-monit/hgccfdagfbilbdbkgmfdmmdfmjjoakfo/related?hl=en

@Indigo I'm located in WV.  Thanks for the link for the monitor will check it out!

I live in NJ and use the same Chrome extension. I basically dedicated a spare laptop directly connected to my own modem. I turned my laptop as a hotspot for rest of the family to connect.  Once I got the Xfinity gateway, this laptop is now connected to that. 

So far, no drops for the past 3 days. I am going to call it solved after watching this whole work week. I will keep this posted.

I did one more thing - sent a mail from here - https://support.xfinity.com/svp-contact-form. Not sure of that helped though.

Thnx for that link sam - bookmarked for future reference in case I need it - I assume you never got a reply? Which brings up a big nit of mine - Comcast has changed the way these forums work, when you hit reply it loads a blank page, you can't see the post you're replying to or the thread - that makes it hard to correctly respond.

Geeze - you're not going to believe this - while writing this post I lost my internet connection again, from 10:53 am to 11:01 am. What's really weird is it appears that it was related to IPv6, which in theory has no role in internet connections, although looking at my PC's TCP/UDP port connections I see plenty of IPv6 UDP and TCP connections, like AVG Free AVGSvc.exe TCPV6 . This is part of what I see after running netstat -s, my PC is definitely using IPv6, for what purpose I know not :

TCP Statistics for IPv6

Active Opens = 38
Passive Opens = 31
Failed Connection Attempts = 19
Reset Connections = 2
Current Connections = 2
Segments Received = 1122
Segments Sent = 1108
Segments Retransmitted = 14

See below for screenshot of what I was seeing while the internet was down - note network adapter is showing no IPv6 connection and I can't resolve most DNS servers:

I have IPv6 enabled on my separate R7000 for the LAN but not WAN.  So WAN is IPv4 only.  I haven't quite figured out the appropriate config on the router for the WAN for IPv6.  My SB6141 does show IPv6 only as the Modem's IP Mode.  So it appears the modem is using IPv6.  One thing I would recommend, Comcast is notorious for DNS issues.  For IPv4, if you can I recommend setting your DNS to the following Google DNS:

DNS1:  8.8.8.8

DNS2:  8.8.4.4

These seem to work faster and are a LOT more stable than relying on Comcast DNS.  

For IPv6 Google DNS appears to be the following:

DNS1:  2001:4860:4860::8888

DNS2: 2001:4860:4860::8844

I switch DNS servers using the DNS Jumper app - Level 3 is available more often than even Google DNS.  Doesn't seem to matter whether I enable IPv6 of my NIC or not, the PC and/or modem is using it for something. Been having connection losses almost evey other minute for the last two days, longest connect time was this morning 2:00 am to 6:00 am - going to have to get Comcast techs out to my house to check the green box signal amplifiers described in this thread near the bottom:

https://forums.xfinity.com/t5/Your-Home-Network/Major-Internet-Issues-Any-Ideas-RESOLVED/td-p/3375432

Really bizarre that I had a solid connection from Sunday afternoon until Monday around 11:00 am, then everything went wonky again. Only thing that changed was I turned off the PC while I was away and rebooted on Sunday, but DNS Jumper flushes the PC's DNS cache automatically so I don't think that has anything to do with it.