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