Apex domains cannot have CNAME records.
Question and response
Question
dig light-speed.de. NS
Answer
light-speed.de. 5 NS ns2.light-speed.de.
light-speed.de. 5 NS ns.light-speed.de.
Authority
The response has no authority records.
Additional
ns.light-speed.de. 5 A 85.214.38.116
ns2.light-speed.de. 5 A 85.214.83.151
ns.light-speed.de. 5 AAAA 2a01:238:43f2:8900:dd04:e3a0:ee11:a73d
ns2.light-speed.de. 5 AAAA 2a01:238:4275:4d00:b851:6489:fb18:f738
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0