Apex domains cannot have CNAME records.
Question and response
Question
dig sib-inet.ru. NS
Answer
SIB-INET.RU. 4 NS ns2.sib-inet.ru.
SIB-INET.RU. 4 NS ns1.sib-inet.ru.
Authority
The response has no authority records.
Additional
ns1.sib-inet.ru. 4 A 134.19.151.186
ns2.sib-inet.ru. 4 A 134.19.151.187
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0