Apex domains cannot have CNAME records.
Question and response
Question
dig traffics-switch.de. NS
Answer
traffics-switch.de. 5 NS nsa8.schlundtech.de.
traffics-switch.de. 5 NS nsc8.schlundtech.de.
traffics-switch.de. 5 NS nsb8.schlundtech.de.
traffics-switch.de. 5 NS nsd8.schlundtech.de.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0