Apex domains cannot have CNAME records.
Question and response
Question
dig tdcnet.fi. NS
Answer
tdcnet.fi. 1 NS ltt-dns-01.tdcnet.fi.
tdcnet.fi. 1 NS ari-dns-01.tdcnet.fi.
tdcnet.fi. 1 NS ldg-dns-01.tdcnet.fi.
Authority
The response has no authority records.
Additional
ari-dns-01.tdcnet.fi. 1 A 62.236.49.41
ldg-dns-01.tdcnet.fi. 1 A 80.64.12.65
ltt-dns-01.tdcnet.fi. 1 A 194.100.90.53
ari-dns-01.tdcnet.fi. 1 AAAA 2001:6e8:0:1:0:0:4:2
ldg-dns-01.tdcnet.fi. 1 AAAA 2001:6e8:0:1:0:0:5:2
ltt-dns-01.tdcnet.fi. 1 AAAA 2001:6e8:0:1:0:0:3:2
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0