Apex domains cannot have CNAME records.
Question and response
Question
dig tnnet.fi. NS
Answer
tnnet.fi. 5 NS safiiri.tnnet.fi.
tnnet.fi. 5 NS ns2.z.fi.
tnnet.fi. 5 NS ns1.z.fi.
tnnet.fi. 5 NS timantti.tnnet.fi.
Authority
The response has no authority records.
Additional
safiiri.tnnet.fi. 5 A 89.236.110.3
timantti.tnnet.fi. 5 A 217.112.240.11
safiiri.tnnet.fi. 5 AAAA 2001:40e8:0:12:89:236:110:3
timantti.tnnet.fi. 5 AAAA 2001:40e8:0:10:217:112:240:11
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0