Apex domains cannot have CNAME records.
Question and response
Question
dig fiberstaden.net. NS
Answer
fiberstaden.net. 5 NS ns2.ipv6dns.se.
fiberstaden.net. 5 NS ns.fiberstaden.se.
fiberstaden.net. 5 NS ns1.ipv6dns.se.
Authority
The response has no authority records.
Additional
ns.fiberstaden.se. 5 A 80.86.70.9
ns1.ipv6dns.se. 5 A 192.71.21.35
ns1.ipv6dns.se. 5 AAAA 2001:67c:2448:10:0:0:0:53
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0