Apex domains cannot have CNAME records.
Question and response
Question
dig sky-barn.avantel.ru. NS
Answer
sky-barn.avantel.ru. 2 NS ns.barnaul.avantel.ru.
sky-barn.avantel.ru. 2 NS ns00.sky.avantel.ru.
sky-barn.avantel.ru. 2 NS ns01.sky.avantel.ru.
Authority
The response has no authority records.
Additional
ns.barnaul.avantel.ru. 2 A 93.91.172.2
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0