Apex domains cannot have CNAME records.
Question and response
Question
dig CONVEX-TAGIL.RU. NS
Answer
CONVEX-TAGIL.RU. 5 NS ns.CONVEX-TAGIL.RU.
CONVEX-TAGIL.RU. 5 NS ns2.CONVEX-TAGIL.RU.
Authority
The response has no authority records.
Additional
ns.convex-tagil.ru. 5 A 109.198.104.10
ns2.convex-tagil.ru. 5 A 31.25.30.134
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0