Community Forum

DNS issues

MMTanner
New Poster

DNS issues

I’ve been having ongoing issues with DNS. I’ve called in and either they don’t understand what I’m saying or don’t have any suggestions.

Name resolution will stop for me over UDP (which is standard for DNS). This is true regardless of which server I use. If I resolve via TCP, however, resolution always works.

I need to know what the issue is with DNS. It’s not a connectivity thing - pings/traceroute works fine and TCP resolution always works. But more and more frequently, DNS fails and connectivity drops as a result.

Anyone have any ideas?
jlavaseur
Valued Contributor

Re: DNS issues

Basically you have to use what protocol works best for you, you don't specify what you are using, udp is faster then tcp, but udp don't always work

flatlander3
Regular Contributor

Re: DNS issues

Well, if Xfinity isn't working, and you can't change the DNS settings on your gateway to point to alternative DNS servers, run one yourself.

 

Bind 9 recursive forward only down and dirty, no local ACL's. 

options{
        directory "/var/cache/bind";
      	recursion yes;
        forwarders {
                1.1.1.1;
                1.0.0.1;
         };
	 forward only;

}

Then point your devices/clients at your server.  New Bind will have the dnssec lines in the .conf file too.  Then your DNS server talks to cloudflare and keeps a local cache.

MMTanner
New Poster

Re: DNS issues

The same issues exist regardless of which server I use. I’ve pointed to Cloudfare, Google, etc. UDP fails to all.
MMTanner
New Poster

Re: DNS issues

UDP. DNS uses UDP unless the request is greater than 512. My follow up would be - how do I force all of my devices to use TCP?

But the more important question is - why is UDP not working with my Comcast connection? It has to be a router thing since it fails to any server I try.
flatlander3
Regular Contributor

Re: DNS issues

No method that I know of to force tcp only, and there is no option for bind to exclusively use TCP.  It will use TCP for a zone transfer, maybe a notify......but I think that's it.

 

Perhaps @ComcastMichele  can point you to a network admin? 

MMTanner
New Poster

Re: DNS issues

Is anyone able to assist? The issue continues daily - every device.
jlavaseur
Valued Contributor

Re: DNS issues

Just out of curiosity, are you using a vpn?

MMTanner
New Poster

Re: DNS issues

The name resolution isn't over a VPN. I do use a VPN on my laptop for work, but this issue exists regardless of if VPN is active and actually sometimes prevents me from connecting to VPN because the name can't be resolved. The VPN for my work is a split tunnel, so resolution (since the Name Servers aren't part of my corporate IP space) doesn't traverse the VPN.

 

No other device in my house uses VPN and it exists on those devices as well.

 

 

MMTanner
New Poster

Re: DNS issues

I have screen recordings of resolution attempts to different servers if it will help at all. It's clear normal resolution fails everytime and TCP resolution works every time.

 

Something is killing UDP over my connection for DNS and I need to identify what it is. I haven't seen any setting in the FW which should be doing it and I would expect any FW setting blocking external DNS for a consumer device wouldn't be very popular.

MMTanner
New Poster

Re: DNS issues

I exchanged my router today. They gave me a different model. I’ll keep an eye on it, but seems to be working so far.
ComcastAbbie
Official Employee

Re: DNS issues

Hello, @MMTanner I am glad to hear that swapping your equipment has seemed to resolve your issue! If anything else comes up, or you notice more issues, please let us know. We are happy to help. 


I am an Official Comcast Employee.
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