Apex domains cannot have CNAME records.
Question and response
Question
dig ipv6.CARNet.hr. NS
Answer
ipv6.CARNet.hr. 5 NS ns2.ipv6.CARNet.hr.
ipv6.CARNet.hr. 5 NS ns1.ipv6.CARNet.hr.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0