Apex domains cannot have CNAME records.
Question and response
Question
dig cesca.es. NS
Answer
cesca.es. 4 NS ns2.cesca.es.
cesca.es. 4 NS chico.rediris.es.
cesca.es. 4 NS ns1.cesca.es.
cesca.es. 4 NS sun.rediris.es.
Authority
The response has no authority records.
Additional
sun.rediris.es. 1 A 199.184.182.1
chico.rediris.es. 1 A 162.219.54.2
sun.rediris.es. 1 AAAA 2620:171:808:0:0:0:0:1
chico.rediris.es. 1 AAAA 2620:10a:80eb:0:0:0:0:2
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0