Apex domains cannot have CNAME records.
Question and response
Question
dig rt-comm.ru. NS
Answer
rt-comm.ru. 5 NS ns02.rtcomm.ru.
rt-comm.ru. 5 NS ns03.rtcomm.ru.
rt-comm.ru. 5 NS ns01.rtcomm.ru.
Authority
The response has no authority records.
Additional
ns01.rtcomm.ru. 5 A 81.176.77.99
ns02.rtcomm.ru. 5 A 81.176.77.115
ns03.rtcomm.ru. 5 A 212.16.193.3
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0