Apex domains cannot have CNAME records.
Question and response
Question
dig v6.cust.suomicom.net. NS
Answer
v6.cust.suomicom.net. 5 NS ns2.suomicom.fi.
v6.cust.suomicom.net. 5 NS ns1.suomicom.fi.
Authority
The response has no authority records.
Additional
ns1.suomicom.fi. 4 A 217.119.36.5
ns2.suomicom.fi. 4 A 217.119.37.5
ns1.suomicom.fi. 4 AAAA 2a00:1190:53:aa1:0:0:0:1
ns2.suomicom.fi. 4 AAAA 2a00:1190:53:aa2:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0