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

[Kai Krakow]

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:

Mai 06 14:17:09 jupiter systemd-resolved[5585]: Cache miss for ssl.gstatic.com IN AAAA
Mai 06 14:17:09 jupiter systemd-resolved[5585]: Transaction 54375 for <ssl.gstatic.com IN AAAA> scope dns on enp5s0/*.
Mai 06 14:17:09 jupiter systemd-resolved[5585]: Using feature level UDP for transaction 54375.
Mai 06 14:17:09 jupiter systemd-resolved[5585]: Using DNS server fe80::b248:7aff:fee7:f438%2 for transaction 54375.
Mai 06 14:17:09 jupiter systemd-resolved[5585]: Sending query packet with id 54375.
Mai 06 14:17:09 jupiter systemd-resolved[5585]: Timeout reached on transaction 33004.
Mai 06 14:17:09 jupiter systemd-resolved[5585]: Retrying transaction 33004.
Mai 06 14:17:09 jupiter systemd-resolved[5585]: Switching to DNS server 2a02:8109:1ec0:6f5:5667:51ff:feea:385f for interface enp5s0.
Mai 06 14:17:09 jupiter systemd-resolved[5585]: Cache miss for ssl.gstatic.com IN A
Mai 06 14:17:09 jupiter systemd-resolved[5585]: Transaction 33004 for <ssl.gstatic.com IN A> scope dns on enp5s0/*.
Mai 06 14:17:09 jupiter systemd-resolved[5585]: Using feature level UDP for transaction 33004.
Mai 06 14:17:09 jupiter systemd-resolved[5585]: Using DNS server 2a02:8109:1ec0:6f5:5667:51ff:feea:385f for transaction 33004.
Mai 06 14:17:09 jupiter systemd-resolved[5585]: Sending query packet with id 33004.
Mai 06 14:17:09 jupiter systemd-resolved[5585]: Processing incoming packet on transaction 33004. (rcode=SUCCESS)
Mai 06 14:17:09 jupiter systemd-resolved[5585]: Not validating response for 33004, used server feature level does not support DNSSEC.
Mai 06 14:17:09 jupiter systemd-resolved[5585]: Added positive unauthenticated cache entry for ssl.gstatic.com IN A 143s on */INET6/2a02:8109:1ec0:6f5:5667:51ff:feea:385f
Mai 06 14:17:09 jupiter systemd-resolved[5585]: Transaction 33004 for <ssl.gstatic.com IN A> on scope dns on enp5s0/* now complete with <success> from network (unsigned).
Mai 06 14:17:09 jupiter systemd-resolved[5585]: Sending response packet with id 42127 on interface 1/AF_INET.
Mai 06 14:17:09 jupiter systemd-resolved[5585]: Sending response packet with id 22131 on interface 1/AF_INET.
Mai 06 14:17:09 jupiter systemd-resolved[5585]: Processing incoming packet on transaction 54375. (rcode=SUCCESS)
Mai 06 14:17:09 jupiter systemd-resolved[5585]: Not validating response for 54375, used server feature level does not support DNSSEC.
Mai 06 14:17:09 jupiter systemd-resolved[5585]: Added positive unauthenticated cache entry for ssl.gstatic.com IN AAAA 203s on enp5s0/INET6/fe80::b248:7aff:fee7:f438
Mai 06 14:17:09 jupiter systemd-resolved[5585]: Transaction 54375 for <ssl.gstatic.com IN AAAA> on scope dns on enp5s0/* now complete with <success> from network (unsigned).
Mai 06 14:17:09 jupiter systemd-resolved[5585]: Freeing transaction 33004.
Mai 06 14:17:09 jupiter systemd-resolved[5585]: Sent message type=method_return sender=n/a destination=:1.352 object=n/a interface=n/a member=n/a cookie=234 reply_cookie=2 error=n/a
Mai 06 14:17:09 jupiter systemd-resolved[5585]: Sent message type=method_call sender=n/a destination=org.freedesktop.DBus object=/org/freedesktop/DBus interface=org.freedesktop.DBus member=RemoveMatch cookie=235 reply_cookie=0 erro
Mai 06 14:17:09 jupiter systemd-resolved[5585]: Got message type=method_return sender=org.freedesktop.DBus destination=:1.273 object=n/a interface=n/a member=n/a cookie=181 reply_cookie=235 error=n/a
Mai 06 14:17:09 jupiter systemd-resolved[5585]: Freeing transaction 54375.

I just don't unterstand why, because all these nameservers work
perfectly well when used directly and not through the stub resolver.


-- 
Regards,
Kai

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