[systemd-devel] systemd-resolved continuously switching DNS servers

[Lennart Poettering]

On Tue, 09.05.17 00:42, Kai Krakow (hurikhan77 at gmail.com) wrote:

> Am Sat, 6 May 2017 14:22:21 +0200
> schrieb Kai Krakow <hurikhan77 at gmail.com>:
> 
> > Am Fri, 5 May 2017 20:18:41 +0200
> > schrieb Lennart Poettering <lennart at poettering.net>:
> > 
> > > On Fri, 05.05.17 01:01, Kai Krakow (hurikhan77 at gmail.com) wrote:
> > >   
> > > > Hello!
> > > > 
> > > > Why is systemd-resolved switching DNS servers all day long? This
> > > > doesn't seem to be right...    
> > > 
> > > If you turn on debug logging, you should see an explanation right
> > > before each switch. I figure we should choose the log levels more
> > > carefully, so that whenever we switch we also log the reason at the
> > > same level...  
> > 
> > It looks like this all has to do with timeouts:
> 
> Fixed by restarting the router. The cable modem seems to be buggy with
> UDP packets after a lot of uptime: it simply silently drops UDP
> packets at regular intervals, WebUI was also very slow, probably a CPU
> issue.
> 
> I'll follow up on this with the cable provider.
> 
> When the problem starts to show up, systemd-resolved is affected more
> by this than direct resolving. I don't know if there's something that
> could be optimized in systemd-resolved to handle such issues better but
> I don't consider it a bug in systemd-resolved, it was a local problem.

Normally configured DNS servers should be equivalent, and hence
switching them for each retry should not come at any cost, hence,
besides the extra log output, do you experience any real issues?

Lennart

-- 
Lennart Poettering, Red Hat