Apex domains cannot have CNAME records.
Question and response
Question
dig gdm.se. NS
Answer
gdm.se. 5 NS ns3.gdmnet.se.
gdm.se. 5 NS ns4.gdmnet.se.
Authority
The response has no authority records.
Additional
ns3.gdmnet.se. 5 A 81.25.80.3
ns4.gdmnet.se. 5 A 217.68.34.4
ns3.gdmnet.se. 5 AAAA 2a06:3640:70:20:0:0:0:2
ns4.gdmnet.se. 5 AAAA 2a06:3640:70:21:0:0:0:2
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0