DNS delay on first lookup, Ubuntu 19.10 but not earlier versions

[Chris Green]

On Wed, Apr 01, 2020 at 08:51:30AM +0100, Colin Law wrote:
> On Tue, 31 Mar 2020 at 22:32, Chris Green <cl at isbd.net> wrote:
> >
> > On Tue, Mar 31, 2020 at 10:19:38PM +0100, Colin Law wrote:
> > > On Tue, 31 Mar 2020 at 21:28, Chris Green <cl at isbd.net> wrote:
> > > >
> > > > I have a small home LAN with dnsmasq running on a Raspberry Pi to
> > > > provide DHCP and DNS services.  I have two systems running xubuntu
> > > > 19.10 and on these systems I see a 5 second delay the *first* time I
> > > > look up the address of a local host.  Subsequent lookups are fast but
> > > > if the system is idle for a long time (I haven't quite fathomed out
> > > > how long) I see the 5 second delay again.
> > >
> > > Do you see anything relevant in syslog at this time?
> > > I think I have seen something like this before.  I have pushed the
> > > problem into my subconscious and hope that when I wake up in the
> > > morning the memory will be recalled.  Or maybe not .....
> > >
> > No, nothing of great relevance.  It only confirms what my tcpdump
> > output shows really.
> 
> Could you post what you see in syslog please, it may trigger my memory recall.
> 
Aha!  This is in the syslog:-

    Apr  1 10:30:13 t470 systemd-resolved[528]: Using degraded feature set (UDP) for DNS server 192.168.1.4.
    Apr  1 10:30:18 t470 NetworkManager[643]: <warn>  [1585733418.9006] dhcp6 (wlp4s0): request timed out
    Apr  1 10:30:18 t470 NetworkManager[643]: <info>  [1585733418.9007] dhcp6 (wlp4s0): state changed unknown -> timeout
    Apr  1 10:30:18 t470 NetworkManager[643]: <info>  [1585733418.9008] dhcp6 (wlp4s0): canceled DHCP transaction
    Apr  1 10:30:18 t470 NetworkManager[643]: <info>  [1585733418.9008] dhcp6 (wlp4s0): state changed timeout -> done

So it's NetworkManager that's timing out, not actually
systemd-resolved.  

Maybe I need to search for NetworkManager dns timeout, or something.


-- 
Chris Green