Apex domains cannot have CNAME records.
Question and response
Question
dig broadband.corbina.ru. NS
Answer
broadband.corbina.ru. 5 NS dns1.corbina.net.
broadband.corbina.ru. 5 NS dns2.corbina.net.
Authority
The response has no authority records.
Additional
dns1.corbina.net. 5 A 213.234.192.1
dns2.corbina.net. 5 A 85.21.192.1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0