Apex domains cannot have CNAME records.
Question and response
Question
dig sibdc.ru. NS
Answer
sibdc.ru. 5 NS ns2.snt.ru.
sibdc.ru. 5 NS ns1.snt.ru.
Authority
The response has no authority records.
Additional
ns1.snt.ru. 5 A 213.59.199.160
ns2.snt.ru. 5 A 188.128.82.232
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0