Apex domains cannot have CNAME records.
Question and response
Question
dig CDn.GbLNet.RU. NS
Answer
CDn.GbLNet.RU. 5 NS ns1.CDn.GbLNet.RU.
CDn.GbLNet.RU. 5 NS ns.GbLNet.RU.
Authority
The response has no authority records.
Additional
ns.GbLNET.ru. 5 A 95.140.80.1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0