Apex domains cannot have CNAME records.
Question and response
Question
dig net.msc-net.cz. NS
Answer
net.msc-net.cz. 4 NS posta.msc-net.cz.
net.msc-net.cz. 4 NS ns1.msc-net.cz.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0