Apex domains cannot have CNAME records.
Question and response
Question
dig core.noris.net. NS
Answer
core.noris.net. 2 NS dns.noris.net.
core.noris.net. 2 NS dns.noris.de.
core.noris.net. 2 NS dns.noris.ch.
Authority
The response has no authority records.
Additional
dns.noris.ch. 2 A 194.31.2.65
dns.noris.de. 2 A 192.109.102.65
dns.noris.net. 2 A 213.95.0.65
dns.noris.de. 2 AAAA 2001:780:53d2:0:0:0:0:53
dns.noris.net. 2 AAAA 2001:780:53d1:0:0:0:0:53
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0