Apex domains cannot have CNAME records.
Question and response
Question
dig den.RU. NS
Answer
den.ru. 4 NS ve.nu.
den.ru. 4 NS ns2.den.ru.
Authority
The response has no authority records.
Additional
ve.nu. 4 A 193.26.18.2
ns2.den.ru. 4 A 87.239.144.1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0