Apex domains cannot have CNAME records.
Question and response
Question
dig ZCDN.RU. NS
Answer
zcdn.ru. 4 NS ams.loky.pw.
zcdn.ru. 4 NS ns1.zcdn.ru.
zcdn.ru. 4 NS ns2.zcdn.ru.
Authority
The response has no authority records.
Additional
ns1.zcdn.RU. 4 A 91.90.212.21
ns2.zcdn.RU. 4 A 77.87.215.24
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0