Apex domains cannot have CNAME records.
Question and response
Question
dig eanet.cz. NS
Answer
eanet.cz. 5 NS hera.eanet.cz.
eanet.cz. 5 NS zeus.eanet.cz.
Authority
The response has no authority records.
Additional
hera.eanet.cz. 5 A 62.168.59.68
zeus.eanet.cz. 5 A 62.168.59.247
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0