Apex domains cannot have CNAME records.
Question and response
Question
dig RENTER.RU. NS
Answer
RENTER.RU. 5 NS ns1.agava.net.RU.
RENTER.RU. 5 NS ns2.agava.net.RU.
Authority
The response has no authority records.
Additional
ns1.agava.net.ru. 5 A 194.58.117.11
ns1.agava.net.ru. 5 A 194.58.117.13
ns1.agava.net.ru. 5 A 194.58.117.15
ns1.agava.net.ru. 5 A 194.58.117.17
ns2.agava.net.ru. 5 A 194.58.117.12
ns2.agava.net.ru. 5 A 194.58.117.14
ns2.agava.net.ru. 5 A 194.58.117.16
ns2.agava.net.ru. 5 A 194.58.117.18
ns1.agava.net.ru. 5 AAAA 2a00:f940:4:0:0:0:0:47
ns2.agava.net.ru. 5 AAAA 2a00:f940:5:0:0:0:0:190
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0