I'm looking for glue record for ns1.push.mobi so I ask one of the root
It gives me the list of dot mobi authorized name servers.
I'm expecting it to be answered by one of the mobi tld authorized name
servers, but it's telling me that it delegates the answer to
ns1.push.mobi instead. It does not make sense for me because how can I
ask ns1.push.mobi if I don't know its ip address yet...
Did you bother to read the response? The glue records are
in the *additional* section. Iterative resolvers know to
look in the additional section to find glue records.