Apex domains cannot have CNAME records.
Question and response
Question
dig pirix.ru. NS
Answer
pirix.ru. 5 NS ns02.comfortel.pro.
pirix.ru. 5 NS ns01.comfortel.pro.
Authority
The response has no authority records.
Additional
ns01.comfortel.pro. 3 A 45.140.76.11
ns02.comfortel.pro. 3 A 45.140.76.21
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0