inconsistent ddns behaviour

Rick Dicaire kritek at
Sun Mar 26 22:53:39 UTC 2017

There is no zone directive in the subnet declaration. Why are ddns updates
being sent for that subnet?

On Sun, Mar 26, 2017 at 5:59 PM, Simon Hobson <dhcp1 at>

> Rick Dicaire <kritek at> 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 ( 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.
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aRDy Music and Rick Dicaire present:
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