Apex domains cannot have CNAME records.
Question and response
Question
dig vtt.fi. NS
Answer
vtt.fi. 5 NS ns2.edelkey.net.
vtt.fi. 5 NS ns-secondary.funet.fi.
vtt.fi. 5 NS ns1.edelkey.net.
Authority
The response has no authority records.
Additional
ns1.edelkey.net. 5 A 213.138.147.136
ns2.edelkey.net. 5 A 213.138.147.137
ns-secondary.funet.fi. 5 A 128.214.248.132
ns-secondary.funet.fi. 5 AAAA 2001:708:10:55:0:0:0:53
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0