Apex domains cannot have CNAME records.
Question and response
Question
dig versatel.de. NS
Answer
versatel.de. 5 NS ns03.versatel.de.
versatel.de. 5 NS ns01.versatel.de.
versatel.de. 5 NS ns02.versatel.de.
Authority
The response has no authority records.
Additional
ns01.versatel.de. 5 A 212.7.128.162
ns02.versatel.de. 5 A 212.7.128.165
ns03.versatel.de. 5 A 193.219.15.17
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0