ns01.vcvn.de has no CNAME records.
Question and response
Question
dig ns01.vcvn.de. NS
Answer
The response has no answer records.
Authority
vcvn.de. 10800 SOA ns15.domserver.de. support.gerwan.de. 2018042300 43200 7200 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0