Apex domains cannot have CNAME records.
Question and response
Question
dig ibericaderedes.es. NS
Answer
ibericaderedes.es. 5 NS ns1101.ui-dns.biz.
ibericaderedes.es. 5 NS ns1023.ui-dns.com.
ibericaderedes.es. 5 NS ns1054.ui-dns.org.
ibericaderedes.es. 5 NS ns1122.ui-dns.de.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0