Apex domains cannot have CNAME records.
Question and response
Question
dig MSTN.RU. NS
Answer
mstn.ru. 5 NS ns1.mstn.ru.
mstn.ru. 5 NS ns2.mstn.ru.
Authority
The response has no authority records.
Additional
ns1.mstn.RU. 5 A 93.174.128.32
ns2.mstn.RU. 5 A 77.247.242.222
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0