Apex domains cannot have CNAME records.
Question and response
Question
dig shortest-route.de. NS
Answer
shortest-route.de. 5 NS ns2.ecircle.de.
shortest-route.de. 5 NS ns3.ecircle.com.
shortest-route.de. 5 NS ns1.ecircle.de.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0