Apex domains cannot have CNAME records.
Question and response
Question
dig vn.ua. NS
Answer
vn.ua. 5 NS ns4.nest.vn.ua.
vn.ua. 5 NS bat.enet.vn.ua.
vn.ua. 5 NS ba1.ns.ua.
vn.ua. 5 NS ho1.ks.ns.ua.
vn.ua. 5 NS nix.ns.ua.
vn.ua. 5 NS ns2.vn.ua.
Authority
The response has no authority records.
Additional
bat.enet.vn.ua. 5 A 141.138.120.200
ns2.vn.ua. 5 A 193.243.158.3
ns4.nest.vn.ua. 5 A 193.243.158.22
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0