Problem with zone delegation with private gTLD

[Matthew Pounsett]

On Mon, 8 Apr 2019 at 10:35, Xavier Humbert
<xavier.humbert at ac-nancy-metz.fr> wrote:
>
> On 08/04/2019 13:05, Matus UHLAR - fantomas wrote:
> > I believe there should be reserved gTLD for such usage.
>
> Is this not what the TLD /.invalid/ is supposed to be ?

RFC2606 reserves test, example, invalid, and localhost, for "testing
and documentation," which seems to fit this use-case.  'invalid'
doesn't seem to me to be intended for use as a generic private TLD
though, as was suggested up-thread.  However, if the OP is setting up
a private network, with no Internet connection, for a demonstration,
then any TLD at all could be used; a private root will be required
regardless.