Apex domains cannot have CNAME records.
Question and response
Question
dig gda.nodea.net.pl. NS
Answer
gda.nodea.net.pl. 4 NS ns2.nodea.net.pl.
gda.nodea.net.pl. 4 NS ns1.nodea.net.pl.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0