check.sidnlabs.nl has no CNAME records.
Question and response
Question
dig check.sidnlabs.nl. NS
Answer
The response has no answer records.
Authority
sidnlabs.nl. 60 SOA ns1.sidnlabs.nl. hostmaster.sidn.nl. 40259 14400 3600 604800 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0