dig +norecurse behaviour changed with 9.16.33

[Greg Choules]

Hi Veronique.
No, we cannot easily reproduce this behaviour because we have no knowledge
of the configs of either of those servers, the details of the zones you
have configured, the contents of those zones or of the system on which you
are running the dig command.

As I said, we need to see everything please:
- Full digs, not +short
- you have specified @ip-dns0 and @ip-dns1 - the full configs of both of
those servers please, including zone definitions and contents for where "
spectrum.cern.ch" lives as it is not a name that can be resolved from the
public Internet
- a binary pcap file, using the -w option of tcpdump, capturing all port 53
traffic (UDP and TCP) between this machine and both DNS servers.

By the way, when using the @<server> option of dig please use explicit IP
addresses, not names. If you use a name, then dig first has to resolve that
name and the place it will go to do that is resolv.conf. So it is now
dependent on your system DNS setup to get an IP address to send the dig to.
Also, you have specified @<simple_host_name> not @<FQDN>. This suggests to
me that in resolv.conf you have a 'search' list. Personally I don't like
search lists because they potentially increase the workload of the DNS
system generally, lengthen query times and mean that you can't be sure
exactly where an answer came from.

Thanks, Greg


On Thu, 27 Oct 2022 at 08:08, Veronique Lefebure <veronique.lefebure at cern.ch>
wrote:

> Hi all,
>
> yes, here is a concrete example:
>
> # ip-dns-1 runs BIND 9.16.33:
>
> dig @ip-dns-1 spectrum.cern.ch +short +norecurse
> spectrum-lb.cern.ch.     <------------- Here we get only the CNAME
>
> # ip-dns-0 runs BIND 9.11:
>
> dig @ip-dns-0 spectrum.cern.ch +short +norecurse
> spectrum-lb.cern.ch.
> xxx.xxx.xx.140         <-------- Here we get in addition the IP of
> spectrum-lb.cern.ch.
>
>
> And yes, a capture shows confirms indeed that dig returns less information
> when the BIND 9.16.33 DNS server is used.
>
> I guess you can easily reproduce that behaviour, unless it is due to a
> mis-configuration bit on our DNS server ?
>
> Thanks,
> Véronique
>
> On 26/10/2022 21:04 Greg Choules <gregchoules+bindusers at googlemail.com>
> wrote:
>
>
> Hi Veronique.
> As other people have said, more details please.
>
> To have a complete picture of what is going on, not only would we need to
> know what your dig tests look like, but also where dig is sending its
> queries and how that DNS server is configured.
>
> You can tell dig to send queries anywhere, using @<server>. However, if
> you don't use that it will default to using the nameservers in
> /etc/resolv.conf. So it may be useful to see the contents of that.
>
> Wherever dig is sending its queries, we would need to know what that
> server will do with them. So its configuration would also be useful.
>
> Lastly, the best way to see queries and responses, right down to the nuts
> and bolts, is with a packet capture.
>
> You thought this was an easy question, huh ;)
>
> Can you provide at least some of these things, to get started?
>
> Cheers, Greg
>
> On Wed, 26 Oct 2022 at 16:41, Veronique Lefebure <
> veronique.lefebure at cern.ch> wrote:
>
> Hi,
>
> dig answer is different between BIND 9.11 and BIND 9.16(.33) when
> +norecurse option is used.
> Is this documented somewhere ?
>
> Is there an option that needs to be set so that the behaviour of 9.16 is
> the same as the one in 9.11.
>
> The change is that with 9.16, if the requested name is a CNAME, only the
> CNAME value is returned by dig, while with 9.11 dig would return both the
> CNAME value and the IP of the CNAME.
>
> Thanks,
> Veronique
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