Apex domains cannot have CNAME records.
Question and response
Question
dig cldin.eu. NS
Answer
cldin.eu. 5 NS ipa01.ams02.cldin.eu.
cldin.eu. 5 NS ipa02.ams02.cldin.eu.
cldin.eu. 5 NS ipa01.haa01.cldin.eu.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0