Apex domains cannot have CNAME records.
Question and response
Question
dig sovintel.ru. NS
Answer
sovintel.ru. 5 NS ns2.gldn.net.
sovintel.ru. 5 NS ns1.gldn.net.
sovintel.ru. 5 NS ns3.gldn.net.
Authority
The response has no authority records.
Additional
ns1.gldn.net. 5 A 194.67.2.108
ns2.gldn.net. 5 A 194.67.2.109
ns3.gldn.net. 5 A 194.67.7.1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0