Apex domains cannot have CNAME records.
Question and response
Question
dig dns2b.RU. NS
Answer
dns2b.RU. 5 NS ns3.dns2dns.RU.
dns2b.RU. 5 NS ns5.l3o-dns.RU.
dns2b.RU. 5 NS ns4.dns4dns.RU.
dns2b.RU. 5 NS ns2.dns4u.RU.
dns2b.RU. 5 NS ns1.dns2b.RU.
Authority
The response has no authority records.
Additional
ns1.dns2b.ru. 5 A 176.99.135.106
ns2.dns4u.ru. 5 A 51.250.101.15
ns3.dns2dns.ru. 5 A 5.188.77.142
ns4.dns4dns.ru. 5 A 95.163.140.58
ns5.l3o-dns.ru. 5 A 95.163.90.182
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0