Apex domains cannot have CNAME records.
Question and response
Question
dig rostel.ru. NS
Answer
rostel.ru. 4 NS adns1.south.rt.ru.
rostel.ru. 4 NS ns1.donpac.ru.
rostel.ru. 4 NS ns0.donpac.ru.
Authority
The response has no authority records.
Additional
ns0.donpac.ru. 4 A 178.34.168.30
ns1.donpac.ru. 4 A 178.34.168.31
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0