Apex domains cannot have CNAME records.
Question and response
Question
dig cc-net.de. NS
Answer
cc-net.de. 1 NS ns1.cc-net.de.
cc-net.de. 1 NS ns3.cc-net.hosting.
cc-net.de. 1 NS ns2.cc-net.de.
Authority
The response has no authority records.
Additional
ns1.cc-net.de. 1 A 213.183.80.5
ns2.cc-net.de. 1 A 213.183.81.5
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0