Apex domains cannot have CNAME records.
Question and response
Question
dig dns1.performancehosting.net. NS
Answer
dns1.performancehosting.net. 5 NS dns1.performancehosting.net.
dns1.performancehosting.net. 5 NS dns2.performancehosting.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0