Apex domains cannot have CNAME records.
Question and response
Question
dig isiconnexion.nl. NS
Answer
isiconnexion.nl. 5 NS ns.nscluster.de.
isiconnexion.nl. 5 NS ns.bnamed.uk.
isiconnexion.nl. 5 NS ns.nscluster.no.
isiconnexion.nl. 5 NS ns.bnamed.eu.
isiconnexion.nl. 5 NS ns.bnamed.us.
Authority
The response has no authority records.
Additional
ns.nscluster.no. 5 A 192.99.83.158
ns.nscluster.no. 5 AAAA 2607:5300:205:200:0:0:0:7f7d
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0