Apex domains cannot have CNAME records.
Question and response
Question
dig SIB-INET.RU. NS
Answer
SIB-INET.RU. 5 NS ns1.SIB-INET.RU.
SIB-INET.RU. 5 NS ns2.SIB-INET.RU.
Authority
The response has no authority records.
Additional
ns1.sib-inet.ru. 5 A 134.19.151.186
ns2.sib-inet.ru. 5 A 134.19.151.187
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0