Apex domains cannot have CNAME records.
Question and response
Question
dig sulinet.hu. NS
Answer
sulinet.hu. 5 NS ns1.edu.hu.
sulinet.hu. 5 NS ns3.edu.hu.
sulinet.hu. 5 NS ns2.edu.hu.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0