Apex domains cannot have CNAME records.
Question and response
Question
dig hexonet.net. NS
Answer
hexonet.net. 5 NS ns1012.hexonet.net.
hexonet.net. 5 NS ns3012.hexonet.net.
hexonet.net. 5 NS ns2012.hexonet.net.
Authority
The response has no authority records.
Additional
ns1012.hexonet.net. 5 A 194.50.187.12
ns2012.hexonet.net. 5 A 194.0.182.12
ns3012.hexonet.net. 5 A 193.227.117.12
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0