Apex domains cannot have CNAME records.
Question and response
Question
dig stage.nic.ru. NS
Answer
stage.nic.ru. 5 NS pdns1.infra.nic.ru.
stage.nic.ru. 5 NS pdns3.infra.nic.ru.
stage.nic.ru. 5 NS pdns2.infra.nic.ru.
Authority
The response has no authority records.
Additional
pdns1.infra.nic.ru. 5 A 31.177.71.214
pdns2.infra.nic.ru. 5 A 31.177.65.199
pdns3.infra.nic.ru. 5 A 31.177.65.200
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0