Apex domains cannot have CNAME records.
Question and response
Question
dig crysys.hit.bme.hu. NS
Answer
crysys.hit.bme.hu. 5 NS pavo.hit.bme.hu.
crysys.hit.bme.hu. 5 NS ara.hit.bme.hu.
crysys.hit.bme.hu. 5 NS shamir.crysys.hit.bme.hu.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0