Apex domains cannot have CNAME records.
Question and response
Question
dig fixed.kpn.net. NS
Answer
fixed.kpn.net. 5 NS ns8.kpn.net.
fixed.kpn.net. 5 NS ns7.kpn.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0