Apex domains cannot have CNAME records.
Question and response
Question
dig rt-dc.ru. NS
Answer
RT-DC.ru. 4 NS ns1.ngenix-dns.net.
RT-DC.ru. 4 NS ns2.ngenix-dns.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0