Apex domains cannot have CNAME records.
Question and response
Question
dig vert.no. NS
Answer
vert.no. 5 NS ns1.optical.no.
vert.no. 5 NS srv.vert.no.
Authority
The response has no authority records.
Additional
ns1.optical.no. 5 A 91.205.187.202
srv.vert.no. 5 A 91.205.184.10
srv.vert.no. 5 AAAA 2a02:20c8:10:0:0:0:0:2
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0