On Wed, Dec 13, 2023 at 08:59:05PM +0000, Simon Kelley wrote:
>
>
> On 13/12/2023 15:25, Chris Green wrote:
> > I run dnsmasq version 2.89 on my laptop which is running [x]ubuntu
> > 23.04.
> >
> > I have systemd.resolvd disabled.
> >
> > I'm occasionally seeing the following error when getting a host's IP:-
> >
> > chris$ host homepi
> > ;; communications error to 127.0.0.1#53: timed out
> > homepi has address 192.168.1.113
> > chris$ ps -ef | grep dnsmasq
> > dnsmasq 933 1 0 Dec06 ? 00:00:22 /usr/sbin/dnsmasq -x
> > /run/dnsmasq/dnsmasq.pid
> -u dnsmasq -7 /etc/dnsmasq.d,.dpkg-dist,.dpkg-old,.dpkg-new --local-service
> --trust-anchor=.,20326,8,2,e06d44b80b8f1d39a95c0b0d7c65d08458e880409bbc683457104237c7f8ec8d
>
>
> > chris 86541 3774 0 15:05 pts/1 00:00:00 grep --color=auto
> > dnsmasq
> > chris$
> >
> > As can be seen dnsmasq is running and subsequent queries work without any
> > error (or delay). The above timeout is a few seconds, maybe five or a bit
> > less.
> >
> > There's no dnsmasq related error message in syslog (nothing for today at
> > all). The system homepi is a Raspberry Pi on the same LAN as the laptop
> > running dnsmasq, The error isn't only for one particular host, I've seen
> > it for other systems on my LAN.
> >
> > Can anyone suggest what might be causing the error and/or how to diagnose
> > what's wrong?
> >
>
> It looks like the first query (or its reply) was dropped, host retried,
> and it worked second time around.
>
> Since DNS transport is normally across UDP, which is defined as
> unreliable, this is completely normal. Except that the UDP packets are
> not actually traversing a network, they're going via the lo interface
> within one machine. I'm sure there are circumstances where UDP packets
> can get dropped in the kernel when going via the lo interface, but it
> shouldn't happen very often. Is the machine under heavy load or memory
> pressure? Maybe a network reconfiguration event could drop packets?
>
No, it's not a heavily loaded system by any means. It's a Thinkpad
T470 laptop with an I7 processor and is virtually never worked hard at
all. Just randomly running top now shows:-
top - 09:59:28 up 12:04, 3 users, load average: 0.20, 0.12, 0.10
Tasks: 254 total, 1 running, 253 sleeping, 0 stopped, 0 zombie
%Cpu(s): 1.5 us, 0.2 sy, 0.0 ni, 97.9 id, 0.3 wa, 0.0 hi, 0.0 si,
0.0 st
MiB Mem : 7790.8 total, 296.7 free, 1032.4 used, 6461.8 buff/cache
MiB Swap: 15258.0 total, 15255.5 free, 2.5 used. 6370.8 avail Mem
That's about the way it always is (three users are all me).
What I don't understand is that there's nothing at all in the logs about the
failure/timeout. Can I increase dnsmasq's logging to see if anything shows
up? It's just 'my' laptop so there isn't a lot of DNS.
--
Chris Green
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