Apex domains cannot have CNAME records.
Question and response
Question
dig dih.oleane.net. NS
Answer
dih.oleane.net. 5 NS ns4.oleane.net.
dih.oleane.net. 5 NS ns5.oleane.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0