Apex domains cannot have CNAME records.
Question and response
Question
dig mastertel.ru. NS
Answer
mastertel.ru. 2 NS ns3.mastertel.ru.
mastertel.ru. 2 NS ns1.mastertel.ru.
Authority
The response has no authority records.
Additional
ns1.mastertel.ru. 2 A 217.67.178.162
ns3.mastertel.ru. 2 A 178.238.117.124
ns1.mastertel.ru. 2 AAAA 2a00:be00:0:1:0:0:0:1
ns3.mastertel.ru. 2 AAAA 2a00:be00:0:1:0:0:0:a
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0