Apex domains cannot have CNAME records.
Question and response
Question
dig ipoac.nl. NS
Answer
ipoac.nl. 5 NS ns2.ipoac.nl.
ipoac.nl. 5 NS ns3.ipoac.nl.
ipoac.nl. 5 NS ns1.ipoac.nl.
Authority
The response has no authority records.
Additional
ns1.ipoac.nl. 5 A 84.27.222.8
ns2.ipoac.nl. 5 A 86.80.166.233
ns3.ipoac.nl. 5 A 193.123.38.172
ns1.ipoac.nl. 5 AAAA 2001:1c01:2d0c:7f00:0:0:0:1
ns2.ipoac.nl. 5 AAAA 2a02:a46f:95b7:0:0:0:0:1
ns3.ipoac.nl. 5 AAAA 2603:c022:c003:7000:ade8:47b:2da5:bc03
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0