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 ns4.MASTERHOST.RU.
MASTERHOST.RU. 5 NS ns3.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