ns1.arcor-ip.de has no CNAME records.
Question and response
Question
dig ns1.arcor-ip.de. NS
Answer
The response has no answer records.
Authority
arcor-ip.de. 7200 SOA ns1.arcor-ip.de. hostmaster.adm.arcor.net. 2026022301 28800 14400 1814400 7200
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0