c.sec-ns.de has no CNAME records.
Question and response
Question
dig c.sec-ns.de. NS
Answer
The response has no answer records.
Authority
sec-ns.de. 774 SOA a.prim-ns.de. hostmaster.nexinto.net. 2017120804 28800 7200 604800 1200
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0