Apex domains cannot have CNAME records.
Question and response
Question
dig masterhost.ru. NS
Answer
masterhost.ru. 5 NS ns5.masterhost.ru.
masterhost.ru. 5 NS ns3.masterhost.ru.
masterhost.ru. 5 NS ns4.masterhost.ru.
Authority
The response has no authority records.
Additional
ns3.masterhost.ru. 5 A 90.156.136.117
ns4.masterhost.ru. 5 A 90.156.137.51
ns5.masterhost.ru. 5 A 90.156.133.162
ns3.masterhost.ru. 5 AAAA 2a00:15f8:a000:10:1:1:1:53
ns4.masterhost.ru. 5 AAAA 2a00:15f8:a000:11:1:1:2:53
ns5.masterhost.ru. 5 AAAA 2a00:15f8:a000:12:1:1:3:53
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0