Apex domains cannot have CNAME records.
Question and response
Question
dig eu.level3.net. NS
Answer
eu.level3.net. 3 NS ns2.eu.level3.net.
eu.level3.net. 3 NS ns1.eu.level3.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0