Apex domains cannot have CNAME records.
Question and response
Question
dig renet.io. NS
Answer
renet.io. 5 NS ns4.renet.io.
renet.io. 5 NS ns2.renet.io.
renet.io. 5 NS ns1.renet.io.
renet.io. 5 NS ns.renet.io.
renet.io. 5 NS ns3.renet.io.
Authority
The response has no authority records.
Additional
ns1.renet.io. 5 A 205.251.194.215
ns2.renet.io. 5 A 205.251.199.114
ns3.renet.io. 5 A 205.251.196.9
ns4.renet.io. 5 A 205.251.193.176
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0