Apex domains cannot have CNAME records.
Question and response
Question
dig kpn.net. NS
Answer
kpn.net. 5 NS ns11.kpn.net.
kpn.net. 5 NS ns1.kpn.net.
Authority
The response has no authority records.
Additional
ns1.kpn.net. 5 A 194.151.228.10
ns11.kpn.net. 5 A 213.75.63.33
ns1.kpn.net. 5 AAAA 2a02:a47f:ac:1:0:0:0:153
ns11.kpn.net. 5 AAAA 2a02:a47f:ac:1:0:0:0:1153
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0