Apex domains cannot have CNAME records.
Question and response
Question
dig irondns.eu. NS
Answer
irondns.eu. 5 NS anycast42.irondns.de.
irondns.eu. 5 NS anycast30.irondns.net.
irondns.eu. 5 NS anycx3.irondns.de.
irondns.eu. 5 NS anycast29.irondns.net.
Authority
The response has no authority records.
Additional
anycast30.irondns.net. 5 A 195.253.66.3
anycast30.irondns.net. 5 AAAA 2a01:5b0:6:0:0:0:0:3
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0