Apex domains cannot have CNAME records.
Question and response
Question
dig ERTELECOM.RU. NS
Answer
ertelecom.ru. 5 NS ns8.ertelecom.ru.
ertelecom.ru. 5 NS ns6.ertelecom.ru.
Authority
The response has no authority records.
Additional
ns6.ertelecom.RU. 5 A 79.141.48.1
ns8.ertelecom.RU. 5 A 79.141.49.1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0