Another systemd-resolved problem in 17.04

[Robert Heller]

At Thu, 22 Jun 2017 15:41:44 +0100 "Ubuntu user technical support,  not for general discussions" <ubuntu-users at lists.ubuntu.com> wrote:

> 
> On Thu, Jun 22, 2017 at 10:33:00AM -0400, Robert Heller wrote:
> > At Thu, 22 Jun 2017 15:00:46 +0100 "Ubuntu user technical support, not 
> > for general discussions" <ubuntu-users at lists.ubuntu.com> wrote: 
> > 
> > > On Thu, Jun 22, 2017 at 08:40:45AM -0400, Tom H wrote:
> > > 
> > > ... but why is it switching to a backup DNS server that I haven't specified 
> > anywhere? Not to mention why is 
> > > is it timing out, 192.168.1.2 is a system on the LAN with nothing else to do except DNS
> > 
> > Does 192.168.1.2 have a firewall set up?  Is it set up *correctly*?  Eg does 
> > it happen to block UDP port 53?
> 
> No, it has no firewall and has been working happily providing DNS to
> my LAB for a couple of years.  It's not been changed except for
> 'apt-get' updates for a long time.  It runs Debian.
> 
> > 
> > What is in the log file for 192.168.1.2?
> > 
> Loads of DHCP messages and no DNS ones at all.
> 
> 
> > The IP6 "backup" DNS might be "hard coded" into the DNS query logic somewhere 
> > as a "fall back" (or there might be an obscure conf file with that in it as a 
> > [default] "fall back".
> > 
> My issue *may* be something awry on the LAN that is preventing queries
> getting to 192.168.1.2, I'll do some checks to see if I can find
> anything.
> 
> It would be good to find where the IPV6 fall back comes from though.

It might be something stupid like the default IPV6 address on the NIC, and
systemd-resolved just falls back to "whatever the default IPV6 address on the
default NIC". It might stop using the IPV6 address IFF you disabled IPV6 on
your NIC.  It sounds like you have something wrong on your LAN and the IPV6 
fall back is just a red herring...

> 

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