Apex domains cannot have CNAME records.
Question and response
Question
dig astendo.de. NS
Answer
astendo.de. 5 NS ns3.ip-projects.de.
astendo.de. 5 NS ns4.ip-projects.de.
Authority
The response has no authority records.
Additional
ns3.ip-projects.de. 5 A 217.160.80.161
ns4.ip-projects.de. 5 A 217.160.81.161
ns3.ip-projects.de. 5 AAAA 2001:8d8:fe:53:217:160:80:161
ns4.ip-projects.de. 5 AAAA 2001:8d8:fe:53:217:160:81:161
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0