Apex domains cannot have CNAME records.
Question and response
Question
dig SINTEC.RU. NS
Answer
SINTEC.RU. 5 NS ext01-1.SINTEC.RU.
SINTEC.RU. 5 NS ns2.afraid.org.
Authority
The response has no authority records.
Additional
ext01-1.SINTEC.RU. 5 A 77.95.130.178
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0