long FQDN resolution

[Greg Choules]

I was beaten to it!
It's called QNAME minimisation and is specified here:
https://datatracker.ietf.org/doc/html/rfc9156

In BIND it can be disabled with this statement:
https://bind9.readthedocs.io/en/v9.20.8/reference.html#namedconf-statement-qname-minimization

Hope that helps, Greg

On Thu, 15 May 2025 at 15:32, DEMBLANS Mathieu <demblans.m at mipih.fr> wrote:

> Hello,
>
> I have a question about mecanism for requests of long subdomains FQDN.
>
> Our DNS, which is in recursive configuration, split long fqdn request with
> subdomains requests like :
>
>
>
> Original request from the client to our recursive DNS : *A
> a.b.c.d.example.com <http://a.b.c.d.example.com>*
>
>
>
> Requests done by our DNS to the domain example.com NS:
>
> *A  _.c.d.example.com <http://c.d.example.com>*
>
> *A _b.c.d.example.com <http://b.c.d.example.com>*
>
> *A a.b.c.d.example.com <http://a.b.c.d.example.com>*
>
>
>
> Is it a normal behaviour ?
>
>
>
> This is only done for 4 levels domains (a.b.example.com for example) and
> more, not « normal » fqdn (ex : www.example.com).
>
> What part of the configuration manage this mecanism ?
>
> Is this really usefull ?
>
>
>
> It is problematic for DNSBL requests because it generate a lot of useless
> requests and this kind of service look at the number of requests done
> (usage policy):
>
>
>
>
>
>
>
>
>
>
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