Apex domains cannot have CNAME records.
Question and response
Question
dig UDMVT.RU. NS
Answer
udmvt.ru. 5 NS a.ns.udmvt.ru.
udmvt.ru. 5 NS b.ns.udmvt.ru.
Authority
The response has no authority records.
Additional
a.ns.udmvt.ru. 5 A 78.85.2.1
b.ns.udmvt.ru. 5 A 78.85.3.1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0