[dnsdist] Many "NS ." requests

[Stephane Bortzmeyer]

On Tue, Aug 26, 2025 at 02:52:21PM +0200,
 Winfried via dnsdist <dnsdist at mailman.powerdns.com> wrote 
 a message of 25 lines which said:

> >> topQueries(30)
> >     1  .                                        7906 39.5%
> >
> > Which is probably not normal.
> >
> "." is not on the topQueries() list on a very busy dnsdist (Resolver 
> loadbalancer) here. Is it possibly a (dnsdist) health-check?

Probably not since it is sent to the backend (I can see it by snooping
the link between dnsdist and the backend). Which is strange since, at
least, dnsdist should serve it from its cache.