Apex domains cannot have CNAME records.
Question and response
Question
dig AVANTEL.RU. NS
Answer
AVANTEL.RU. 5 NS ns2.AVANTEL.RU.
AVANTEL.RU. 5 NS ns.AVANTEL.RU.
Authority
The response has no authority records.
Additional
ns.avantel.RU. 5 A 195.49.168.2
ns2.avantel.RU. 5 A 195.49.169.4
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0