Apex domains cannot have CNAME records.
Question and response
Question
dig zoner-asiakas.fi. NS
Answer
zoner-asiakas.fi. 5 NS ns1.zoner.fi.
zoner-asiakas.fi. 5 NS ns2.zoner.fi.
zoner-asiakas.fi. 5 NS ns3.zoner.fi.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0