Apex domains cannot have CNAME records.
Question and response
Question
dig ras.ru. NS
Answer
ras.ru. 5 NS nsb.ras.ru.
ras.ru. 5 NS nsa.ras.ru.
ras.ru. 5 NS nsc.ras.ru.
Authority
The response has no authority records.
Additional
nsa.ras.ru. 5 A 93.174.130.130
nsb.ras.ru. 5 A 93.174.128.32
nsc.ras.ru. 5 A 77.247.242.222
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0