Apex domains cannot have CNAME records.
Question and response
Question
dig zimpel.de. NS
Answer
zimpel.de. 5 NS ns1.de.colt.net.
zimpel.de. 5 NS ns8.colt.net.
Authority
The response has no authority records.
Additional
ns1.de.colt.net. 5 A 212.74.77.55
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0