Getting the name of responding server(s)

[Matthew Pounsett]

On Tue, 7 Sept 2021 at 03:45, Stephane Bortzmeyer <bortzmeyer at nic.fr> wrote:

> The only solution is chasing the delegations from the root (which is
> what dig +trace is doing). Caching speeds it, this is why it is
> better to go through your resolver than using dig +trace.

Yeah, you can pretty reliably get the answer in one or two steps by
requesting the NS set for the FQDN.  You'll either get your answer, or
get an SOA with the name of the enclosing zone.  Second lookup gets
you the NS set for the enclosing zone.  Just using your local
recursive server to deal with tracking down the answer should work
well, unless for some reason you need to see every possible answer
from every delegating name server.

% dig +noall +answer +authority IN NS www.example.net
example.net. 3591 IN SOA ns.icann.org. noc.dns.icann.org. 2021090201
7200 3600 1209600 3600

% dig +noall +answer IN NS example.net
example.net. 86396 IN NS b.iana-servers.net.
example.net. 86396 IN NS a.iana-servers.net.

Or a one-liner that works whether you supply the FQDN or its enclosing zone:
% dig +noall +answer +authority IN NS www.example.net | head -1 | cut
-f 1 | xargs dig +noall +answer IN NS | awk '{print $NF}'
b.iana-servers.net.
a.iana-servers.net.

% dig +noall +answer +authority IN NS example.net | head -1 | cut -f 1
| xargs dig +noall +answer IN NS | awk '{print $NF}'
a.iana-servers.net.
b.iana-servers.net.