ns.opst.de has no CNAME records.
Question and response
Question
dig ns.opst.de. NS
Answer
The response has no answer records.
Authority
opst.de. 7047 SOA ns1.opst.de. support.variomedia.de. 2022101068 28800 7200 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0