Apex domains cannot have CNAME records.
Question and response
Question
dig subnet.zp.ua. NS
Answer
subnet.zp.ua. 4 NS ns2.subnet.zp.ua.
subnet.zp.ua. 4 NS ns1.subnet.zp.ua.
Authority
The response has no authority records.
Additional
ns1.subnet.zp.ua. 4 A 91.218.97.1
ns2.subnet.zp.ua. 4 A 91.218.97.242
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0