Apex domains cannot have CNAME records.
Question and response
Question
dig zonnet.be. NS
Answer
zonnet.be. 2 NS ns.zonnet.org.
zonnet.be. 2 NS ns.zonnet.nl.
zonnet.be. 2 NS ns.zonnet.be.
Authority
The response has no authority records.
Additional
ns.zonnet.be. 2 A 85.119.243.21
ns.zonnet.nl. 2 A 77.95.248.166
ns.zonnet.org. 2 A 31.3.105.149
ns.zonnet.be. 2 AAAA 2a00:e760:100:0:f:1442:0:1
ns.zonnet.nl. 2 AAAA 2a00:1478:20:0:4:157:0:1
ns.zonnet.org. 2 AAAA 2a03:7900:105:31:3:105:149:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0