Re: Very slow DNS lookup with NetworkManager and dnsmasq

Marc Luethi <netztier bluewin ch> writes:

> UDP Checksums and validation.
> So you might want to investigate if...
> - the windows machines that get fast answers do send UDP checksums at
>   all
> - if your machine fills in the UDP checksum when running with dnsmasq
> - if your machine fills in the UDP checksum when running without dnsmasq
> - if DNS datagrams leaving your network have valid UDP checksums
> - if either set of the fast/slow servers do UDP checksum validation on
> incoming datagrams (while accepting datagrams that don't have a
> checksum)
> - if DNS datagrams arriving at the remote DNS server still have valid
> UDP checksums.[2]

Fascinating possibilities... Given that I am neither a system
administrator nor a network specialist, there is a limit to what I can
do. For example, examining traffic leaving our network is, at least in
the short run, out of my scope. What I think that I will do, now that I
have read your post, is to try the following in the next couple of weeks
when I have the time:

1. Disable dnsmasq, since it's really not the troublemaker here, it just
   does not solve the issue.

2. Run dig queries on the fast / slow nameservers, and examine the
   resulting DNS traffic with wireshark to see whether I can spot a

I think I could manage to do that, and even learn something in the
process. Your input was much appreciated.


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