Apex domains cannot have CNAME records.
Question and response
Question
dig licence.lu. NS
Answer
licence.lu. 5 NS ns1.eurodns.com.
licence.lu. 5 NS ns2.eurodns.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0