Apex domains cannot have CNAME records.
Question and response
Question
dig web01.trans-ix.nl. NS
Answer
web01.trans-ix.nl. 5 NS nsauth2.trans-ix.net.
web01.trans-ix.nl. 5 NS nsauth3.trans-ix.com.
Authority
The response has no authority records.
Additional
nsauth2.trans-ix.net. 5 A 185.108.117.31
nsauth3.trans-ix.com. 5 A 37.97.162.245
nsauth2.trans-ix.net. 5 AAAA 2a06:4a80:117:0:0:0:0:31
nsauth3.trans-ix.com. 5 AAAA 2a01:7c8:bb01:851:5054:ff:feb6:6f70
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0