Apex domains cannot have CNAME records.
Question and response
Question
dig ip.serverbox.net. NS
Answer
ip.serverbox.net. 2 NS ns3.dnsbox.net.
ip.serverbox.net. 2 NS ns.dnsbox.net.
ip.serverbox.net. 2 NS ns2.dnsbox.net.
Authority
The response has no authority records.
Additional
ns.dnsbox.net. 2 A 208.53.48.154
ns2.dnsbox.net. 2 A 45.79.100.232
ns3.dnsbox.net. 2 A 108.60.195.215
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0