Apex domains cannot have CNAME records.
Question and response
Question
dig mv.sonera.fi. NS
Answer
mv.sonera.fi. 5 NS ascona.mv.sonera.fi.
mv.sonera.fi. 5 NS corolla.mv.sonera.fi.
Authority
The response has no authority records.
Additional
ascona.mv.sonera.fi. 5 A 192.89.193.53
ascona.mv.sonera.fi. 5 A 193.209.134.53
corolla.mv.sonera.fi. 5 A 195.156.25.26
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0