Apex domains cannot have CNAME records.
Question and response
Question
dig eduroam.nl. NS
Answer
eduroam.nl. 5 NS ns2.surfnet.nl.
eduroam.nl. 5 NS ns3.surfnet.nl.
eduroam.nl. 5 NS ns1.zurich.surf.net.
eduroam.nl. 5 NS ns1.surfnet.nl.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0