Apex domains cannot have CNAME records.
Question and response
Question
dig MTS-NN.RU. NS
Answer
mts-nn.ru. 5 NS ns2.sinn.ru.
mts-nn.ru. 5 NS ns.mts-nn.ru.
Authority
The response has no authority records.
Additional
ns.mts-nn.RU. 5 A 213.177.96.1
ns2.sinn.ru. 5 A 213.177.97.1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0