Apex domains cannot have CNAME records.
Question and response
Question
dig krsk-sbit.ru. NS
Answer
krsk-sbit.ru. 4 NS ns1.krsk-sbit.ru.
krsk-sbit.ru. 4 NS ns8-l2.nic.ru.
krsk-sbit.ru. 4 NS ns4-l2.nic.ru.
Authority
The response has no authority records.
Additional
ns1.krsk-sbit.ru. 4 A 193.105.236.4
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0