Apex domains cannot have CNAME records.
Question and response
Question
dig ipfu.de. NS
Answer
ipfu.de. 5 NS ns113.ovh.net.
ipfu.de. 5 NS dns113.ovh.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0