Apex domains cannot have CNAME records.
Question and response
Question
dig rt-dc.RU. NS
Answer
rt-dc.RU. 4 NS ns2.ngenix-dns.net.
rt-dc.RU. 4 NS ns1.ngenix-dns.net.
Authority
The response has no authority records.
Additional
ns1.ngenix-dns.net. 4 A 212.193.150.254
ns2.ngenix-dns.net. 4 A 212.193.151.254
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0