[Dnsmasq-discuss] Corrupted query causing FORMERR?

[John Horne]

On Sat, 2023-08-19 at 12:17 +0200, Geert Stappers wrote:
> On Fri, Aug 18, 2023 at 09:59:40AM +0000, John Horne wrote:
> > On Thu, 2023-08-17 at 17:08 +0000, John Horne wrote:
> > >
> > > Things tried include, disabling the 'edns0' option in the
> > > /etc/resolv.conf file; setting the max UDP packet size to 1232; setting
> > > the max UDP packet size to 512; using dnsmasq version 2.89. These all
> > > failed in that we still received FORMERR replies.
> > > The only option so far that has worked is to disable the use of dnsmasq
> > > via 127.0.0.1, and let each server send queries direct to the Unbound
> > > server. This has caused no FORMERR replies.
> > >
> > I should add that I have now tried running dnsmasq but with the caching
> > disabled. That too works (using the same simple test used before),
>
> Consider to describe "the same simple test used before" in a clear way
> so it can be reproduced elsewhere.
>
I invoked the following script simply by using 'nohup ./dns-test &' and checked
the output file for FORMERR every so often.

===============
#!/bin/bash

while true; do
date
dig sauopprdwebsite1.blob.core.windows.net
sleep 10
done >~/dns-output

exit
===============


>
> > so it looks like some issue with the caching part of dnsmasq.
>
> Consider to tell more about the cache usage.
>
All I can say is that if I set the cache size to zero ('cache-size=0') then the
problem doesn't occur. If I set it to 'cache-size=2048' (which is our usual
setting), then then problem occurs again.


John.

--
John Horne | Senior Operations Analyst | Technology and Information Services
University of Plymouth | Drake Circus | Plymouth | Devon | PL4 8AA | UK
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