Apex domains cannot have CNAME records.
Question and response
Question
dig xservers.net. NS
Answer
xservers.net. 5 NS nsc.xservers.ro.
xservers.net. 5 NS nsd.xservers.ro.
xservers.net. 5 NS nsa.xservers.ro.
xservers.net. 5 NS nsb.xservers.ro.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0