Apex domains cannot have CNAME records.
Question and response
Question
dig LUGANET.RU. NS
Answer
luganet.ru. 5 NS ns3.luganet.ru.
luganet.ru. 5 NS ns.luganet.ru.
luganet.ru. 5 NS ns2.luganet.ru.
Authority
The response has no authority records.
Additional
ns.LUGANET.RU. 5 A 194.31.155.4
ns2.LUGANET.RU. 5 A 194.31.155.5
ns3.luganet.ru. 5 A 194.31.155.3
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0