Apex domains cannot have CNAME records.
Question and response
Question
dig in-addr.mastertelecom.ru. NS
Answer
in-addr.mastertelecom.ru. 5 NS ns1.mastertel.ru.
in-addr.mastertelecom.ru. 5 NS ns2.mastertel.ru.
Authority
The response has no authority records.
Additional
ns1.mastertel.ru. 5 A 217.67.178.162
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0