Apex domains cannot have CNAME records.
Question and response
Question
dig datacenter.fi. NS
Answer
datacenter.fi. 3 NS ns2.datacenter.fi.
datacenter.fi. 3 NS ns1.datacenter.fi.
Authority
The response has no authority records.
Additional
ns1.datacenter.fi. 3 A 89.250.52.250
ns2.datacenter.fi. 3 A 79.171.224.133
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0