Apex domains cannot have CNAME records.
Question and response
Question
dig core.as8218.eu. NS
Answer
core.as8218.eu. 2 NS ns50.zayo.com.
core.as8218.eu. 2 NS ns60.zayo.com.
Authority
The response has no authority records.
Additional
ns50.zayo.com. 3 A 195.216.193.132
ns60.zayo.com. 3 A 64.125.227.132
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0