Apex domains cannot have CNAME records.
Question and response
Question
dig SERVERS.RU. NS
Answer
SERVERS.RU. 5 NS ns2.he.net.
SERVERS.RU. 5 NS ns1.srvdns.RU.
SERVERS.RU. 5 NS ns1.he.net.
SERVERS.RU. 5 NS ns2.srvdns.RU.
Authority
The response has no authority records.
Additional
ns1.he.net. 5 A 216.218.130.2
ns1.srvdns.ru. 5 A 185.206.100.100
ns2.he.net. 5 A 216.218.131.2
ns2.srvdns.ru. 5 A 88.212.217.180
ns1.he.net. 5 AAAA 2001:470:100:0:0:0:0:2
ns2.he.net. 5 AAAA 2001:470:200:0:0:0:0:2
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0