inconsistent ddns behaviour

[Simon Hobson]

Rick Dicaire <kritek at gmail.com> wrote:

> Hi folks, ISC dhcpd 4.3.4, named 9.11.0-P3.
> I have a ddns configuration that works fine.
> Then I added a new subnet declaration (192.168.18.0) to the conf file, and this subnet conf sent ddns updates as well though I didn't define dns zones to update.
> 
> Is this expected behaviour?

Yes.
The default is to lookup the SOA record for the appropriate zones to find the master DNS server, and send updates (unsigned) to that. Thus with a correctly configured DNS, updates will be generated automagically without any admin intervention.
However, using unsigned updates is considered insecure - and so you should be specifying DNS zones - not to indicate the master DNS, but to specify the signing key.