Apex domains cannot have CNAME records.
Question and response
Question
dig netinstal.pl. NS
Answer
netinstal.pl. 5 NS ns1.netinstal.pl.
netinstal.pl. 5 NS ns2.netinstal.pl.
netinstal.pl. 5 NS ns3.netinstal.pl.
Authority
The response has no authority records.
Additional
ns1.netinstal.pl. 5 A 85.11.68.25
ns2.netinstal.pl. 5 A 85.11.68.26
ns3.netinstal.pl. 5 A 85.11.68.27
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0