Apex domains cannot have CNAME records.
Question and response
Question
dig tdc.fi. NS
Answer
tdc.fi. 5 NS ns-no.sn.net.
tdc.fi. 5 NS ns-se.sn.net.
tdc.fi. 5 NS ns-fi.sn.net.
Authority
The response has no authority records.
Additional
ns-fi.sn.net. 5 A 194.100.90.53
ns-no.sn.net. 5 A 80.64.12.65
ns-se.sn.net. 5 A 62.236.49.41
ns-fi.sn.net. 5 AAAA 2001:6e8:0:1:0:0:3:2
ns-no.sn.net. 5 AAAA 2001:6e8:0:1:0:0:5:2
ns-se.sn.net. 5 AAAA 2001:6e8:0:1:0:0:4:2
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0