Windows 10 DNS Problems
24 Mar

Windows 10 DNS Problems

This week I came accross a strange problem in Windows 10, and since I’m likly to have the same problem in future I thought it worth to record what happened – and how I solved it.

Starting at the beginning I’ll layout the problem. I run my own DNS server on my network both for simple caching and security but mostly to override certain external domains with their internal host. So you can imagine my headache when Firefox starting saying my hosts were unavailable.

After some digging I found, thanks to the ping command, Windows was looking at the wrong IP address. Instead of getting my DNS servers local IP address it was returning the external IP address. My first thoughts were the DNS server was at fault and I spent two or three hours going down that line of thought with no sucess. I finally struck on the idea of using Wireshark to check what was coming back from the DNS server. This at least confirmed that the right – by which I mean local – IP address was returned from DNS which meant Windows was doing some after the fact.

I eventually traced the problem to my Avast anti-virus. Avast has, what in most cases is a really useful – feature called ‘Secure DNS‘ which was intercepting my requests and altering the returned IP. As soon as I disabled this feature my problems were solved.

So I’m posting this here for anyone else whoes having a similar problem. I hope it will help someone else.