Apex domains cannot have CNAME records.
Question and response
Question
dig coreit.se. NS
Answer
coreit.se. 3 NS ns3.coreit.se.
coreit.se. 3 NS ns2.coreit.se.
coreit.se. 3 NS ns1.coreit.se.
Authority
The response has no authority records.
Additional
ns1.coreit.se. 3 A 85.11.198.175
ns2.coreit.se. 3 A 20.73.51.17
ns3.coreit.se. 3 A 81.21.224.20
ns1.coreit.se. 3 AAAA 2a0d:26c0:3:50:0:0:0:18
ns2.coreit.se. 3 AAAA 2603:1020:201:e:0:0:0:170
ns3.coreit.se. 3 AAAA 2a0d:26c0:3:1:0:0:0:10
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0