Apex domains cannot have CNAME records.
Question and response
Question
dig tripledns.eu. NS
Answer
tripledns.eu. 4 NS ns1.hostserv.eu.
tripledns.eu. 4 NS ns3.hostserv.eu.
tripledns.eu. 4 NS ns2.hostserv.eu.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0