Apex domains cannot have CNAME records.
Question and response
Question
dig yandex.ru. NS
Answer
yandex.ru. 4 NS ns2.yandex.ru.
yandex.ru. 4 NS ns1.yandex.ru.
Authority
The response has no authority records.
Additional
ns1.yandex.ru. 4 A 213.180.193.1
ns2.yandex.ru. 4 A 93.158.134.1
ns1.yandex.ru. 4 AAAA 2a02:6b8:0:0:0:0:0:1
ns2.yandex.ru. 4 AAAA 2a02:6b8:0:1:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0