Apex domains cannot have CNAME records.
Question and response
Question
dig rostelecom.ru. NS
Answer
rostelecom.ru. 4 NS ns1.rostelecom.ru.
rostelecom.ru. 4 NS ns2.rostelecom.ru.
rostelecom.ru. 4 NS ns.rt-comm.ru.
Authority
The response has no authority records.
Additional
ns1.rostelecom.ru. 4 A 87.226.162.62
ns2.rostelecom.ru. 4 A 87.226.159.65
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0