Apex domains cannot have CNAME records.
Question and response
Question
dig 9-9-9-9-9.net. NS
Answer
9-9-9-9-9.net. 5 NS ns5.sentia.nl.
9-9-9-9-9.net. 5 NS ns4.sentia.nl.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0