Apex domains cannot have CNAME records.
Question and response
Question
dig win.dtu.dk. NS
Answer
win.dtu.dk. 5 NS dns3.dtu.dk.
win.dtu.dk. 5 NS authdns1.ait.dtu.dk.
win.dtu.dk. 5 NS authdns2.ait.dtu.dk.
Authority
The response has no authority records.
Additional
dns3.dtu.dk. 5 A 130.225.231.123
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0