Apex domains cannot have CNAME records.
Question and response
Question
dig s7host.net. NS
Answer
s7host.net. 5 NS ns1.s7host.net.
s7host.net. 5 NS ns4.s7host.net.
s7host.net. 5 NS ns3.s7host.net.
s7host.net. 5 NS ns2.s7host.net.
Authority
The response has no authority records.
Additional
ns1.s7host.net. 5 A 216.211.21.226
ns2.s7host.net. 5 A 184.68.71.238
ns3.s7host.net. 5 A 169.55.169.61
ns4.s7host.net. 5 A 169.54.67.4
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0