Apex domains cannot have CNAME records.
Question and response
Question
dig core.avantel.ru. NS
Answer
core.avantel.ru. 5 NS ns1.avantel.ru.
core.avantel.ru. 5 NS ns.avantel.ru.
Authority
The response has no authority records.
Additional
ns.avantel.ru. 4 A 195.49.168.2
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0