Apex domains cannot have CNAME records.
Question and response
Question
dig internap.com. NS
Answer
internap.com. 1 NS ns-b.pnap.net.
internap.com. 1 NS ns-a.pnap.net.
internap.com. 1 NS ns-d.pnap.net.
internap.com. 1 NS ns-c.pnap.net.
Authority
The response has no authority records.
Additional
ns-a.pnap.net. 1 A 64.94.123.4
ns-b.pnap.net. 1 A 64.94.123.36
ns-c.pnap.net. 1 A 64.95.61.4
ns-d.pnap.net. 1 A 64.95.61.36
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0