Apex domains cannot have CNAME records.
Question and response
Question
dig ISSR.ru. NS
Answer
issr.ru. 5 NS dns0.mts.ru.
issr.ru. 5 NS dns1.mts.ru.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0