Apex domains cannot have CNAME records.
Question and response
Question
dig cust.trined.nl. NS
Answer
cust.trined.nl. 5 NS dnsauth2.tnoc.nl.
cust.trined.nl. 5 NS dnsauth1.tnoc.nl.
Authority
The response has no authority records.
Additional
dnsauth1.tnoc.nl. 5 A 45.145.108.107
dnsauth2.tnoc.nl. 5 A 45.145.109.107
dnsauth1.tnoc.nl. 5 AAAA 2a0e:fdc0:100:0:0:0:0:2
dnsauth2.tnoc.nl. 5 AAAA 2a0e:fdc0:200:0:0:0:0:2
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0