Intermittent "DNS not working" or "test site can't be reached" on Xfinity

FranklyTechFranklyTech Member Posts: 2
Name Dropper First Comment
  1. For many weeks I've been having intermittent DNS fails, several times a day on my MacBook Pro, connected via Ethernet to the router, via a 24 port switch in the wiring close.
  2. We have 300mbit service, and a recent Comcast node split, so bandwidth doesn't seem to be the issue. And all the wiring into the house from the pole has been checked. 
  3. In addition, iPhones experience very long load times for apps and web sites, intermittently. 
  4. Comcast is our only local provider. I was using the XB6 gateway with xFi Pods. Tech support didn't offer any ideas for the problem, other than restart. And you can't change the DNS supplier on the XB6, it's locked to Comcast's DNS.
  5. So I put the XB6 in Bridge mode and setup an Eero Pro as the router, using Comcast DNS. Same problem. So then I went to custom DNS, using Cloudflare 1.1.1.1 as primary and Google 8.8.8.8 as backup for both IPv4 and IPv6.
  6. Still have the problem.
  7. Note that I have many smart home devices on the network, in addition to four people's worth of laptops and smartphones, plus extras. So there's lots going on in the network. Three or even four of us using video chat at once.
  8. But Fing Desktop software will and post DNS fail notices in the middle of the night when we're all sleeping!
  9. I've got a Fing Box, in addition the Mac app, and the iPhone app.
  10. no clue on what the cause is.
  11. Any suggestions?
In addition to alerts from Fing, I'll get long delays in loading a web site, or 30 second pauses in Microsoft Teams video calls. 
kltaylor

Answers

  • kltaylorkltaylor Moderator, Beta Tester Posts: 1,231
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    HI @FranklyTech, welcome to the community and thanks for asking your question.
    A few things could be happening here, so we need to know a bit more information on your network setup.
    1.)  What DNS IPs are you using?
    2.) What make/model is the router?
    3.)  How old is the router?

    If you feel that this is an issue with the DNS resolution, try using a Public DNS like Google's, Quad9, etc.  Also ensure that there is only one IP subnet in the DNS section, don't add a 'Secondary DNS' at all.
    This could also be an issue with your router depending on its age.  If the router and modem are leased through Comcast, you may wish to request a replacement.
    What I would do is use a machine that you can leave on for a day (24hrs) open a Command Prompt window and issue a constant PING to Google (ping google.com -t) and then another separate Command Prompt window to PING your Gateway/Router address (PING 192.168.1.x -t).  Watch for the moment of any abnormalities and which one drops packet connections.  This can provide to you a means to discover what you're experiencing and move forward from there.
    Please let me know what you find out.
    "There's a fine line between audacity and idiocy."
    -Warden Anastasia Luccio, Captain
    RobinFranklyTech
  • FranklyTechFranklyTech Member Posts: 2
    Name Dropper First Comment
    edited August 14
    Thanks @kltaylor for the quick reply.
    1.) What DNS IPs? - See line 5 -> "custom DNS, using Cloudflare 1.1.1.1 as primary and Google 8.8.8.8 as backup for both IPv4 and IPv6"
    2. What make/model is the router? See line 4 & 5 - XB6 Gateway in bridge mode, Router is Eero Pro, with 2 more Eero Pro as mesh nodes in the house. 
    3. How old is the router? Eero Pro is from 2016, and is still a shipping model. They update firmware regularly. 

    New data point, screen shot below.
    Eero puts its router address as the first DNS address, 192.168.7.1
    Note below that failed. but it got a result from the secondary DNS, Google's 8.8.8.8. 

    And 30 second outages of streaming video or screen sharing have increased in the last two days. 

    I will try the suggestions to:
    - eliminate the secondary DNS, though not sure how that helps
    - get new modem/gateway - Comcast installing an XB7 on Monday. And I hope to try a different mesh router/WiFi system beyond the Eero soon. 
    - for the 24 hour command line test, I have access to a Mac or PC. Any link to more detailed instructions of what this will look like and how to interpret the results?
    - any useful software, beyond Fing, for figuring out what is going on?

    Thanks all!



    kltaylor
  • kltaylorkltaylor Moderator, Beta Tester Posts: 1,231
    1000 Comments 500 Likes 50 Answers 100 Awesomes
    ✭✭✭✭✭✭
    Thanks @kltaylor for the quick reply.
    1.) What DNS IPs? - See line 5 -> "custom DNS, using Cloudflare 1.1.1.1 as primary and Google 8.8.8.8 as backup for both IPv4 and IPv6"
    2. What make/model is the router? See line 4 & 5 - XB6 Gateway in bridge mode, Router is Eero Pro, with 2 more Eero Pro as mesh nodes in the house. 
    3. How old is the router? Eero Pro is from 2016, and is still a shipping model. They update firmware regularly. 

    New data point, screen shot below.
    Eero puts its router address as the first DNS address, 192.168.7.1
    Note below that failed. but it got a result from the secondary DNS, Google's 8.8.8.8. 

    And 30 second outages of streaming video or screen sharing have increased in the last two days. 

    I will try the suggestions to:
    - eliminate the secondary DNS, though not sure how that helps
    - get new modem/gateway - Comcast installing an XB7 on Monday. And I hope to try a different mesh router/WiFi system beyond the Eero soon. 
    - for the 24 hour command line test, I have access to a Mac or PC. Any link to more detailed instructions of what this will look like and how to interpret the results?
    - any useful software, beyond Fing, for figuring out what is going on?

    Thanks all!



    As a minor suggestion, you may want to use a different DNS other than Google's, simply for more privacy and security.  Personally I use Quad9 (9.9.9.9) just for that reason.
    XBS is an XFinity device?  One of the reasons why I have my own hardware while using Comcast services is for the reason that they won't use any of my bandwidth for their 'XFinity Hotspots'.  As an XFinity device, they do exactly that to provide "free" hotspots all around your local area and abroad.
    I'm actually starting to wonder if the outages are a planned thing that they won't talk about.  Even with Comcast Business internet, every Sunday right at 8:05 MST we experience a temporary outage as well.
    I think that investigating the issue is more hardware related than it is software, as Fing Desktop (especially the paid version) will have more than enough tools to use to determine what's happening.  At the very least since the gateway is at least 4 years old, and even though it still works, technology advances every few years.  Just to keep up with the latest wireless capabilities and such, it may be a great idea to consider either requesting that they replace your gateway with a new device (they won't but you can at least request it) or purchase your own so that you know for certain that hardware isn't the issue and press Comcast to fix their stuff.
    I've been down that road more than once, each time they come out to my house they end up replacing something on their side because I am adamant on the effectiveness of my equipment.
    "There's a fine line between audacity and idiocy."
    -Warden Anastasia Luccio, Captain
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