DNS issues with Windows 7

By | 2013-01-26

Note: I have transferred this blog from my old blog site: http://dcarapic.blogspot.com/ so I am reposting most of the stuff from there

Recently I've had a problem with my laptop connected to my home network. For some reason DNS was working intermittently .. meaning that it sometimes worked and sometimes didn't. It also seamed that it was susceptible to throttling .. meaning that if I opened several browser windows at once it would not work. I've scoured the net searching for a solution and was not able to find anything that applied to me. Most of the issues were connected to some 3rd party VPN software or similar.

What really annoyed me was that it was only happening with my laptop and only at home. Finally I found a forum comment somewhere (lost the link unfortunately) where the author stated that turning of IP flood protection on his router fixed the issue for him/her. Reading that I remembered that my router was reset lately (I don't know how, it just happened) so I had to reconfigure it again. During my configuration I turned on IP flood detection (it looks like something you would want to have turned on). So I opened the router configuration and turned off IP flood detection and lo and behold ... everything works great.

How I tested my DNS

Initially I downloaded a small tool called DNS Name Speed Benchmark to determine if there was an issue with my DNS provider but I did not get that much information out of it. It either and all DNS providers could be reached and checked or it did not work at all. After that I just used nslookup command in combination with powershell to run the command in loops.

PS C:\Users\dcarapic> for(1..100) { nslookup www.google.com }

This would execute DNS lookup for the given host (using your default DNS server) a hundred times. During my initial run lookup was time outing here and there and once I tried opening the browser and loading lots of pages it was time-outing all the time. Once I removed the IP flood detection the output of the nslookup was clear and without any time-outs at any time!

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