Apex domains cannot have CNAME records.
Question and response
Question
dig rediris.es. NS
Answer
rediris.es. 5 NS scsnms.switch.ch.
rediris.es. 5 NS sun.rediris.es.
rediris.es. 5 NS ns02.fccn.pt.
rediris.es. 5 NS chico.rediris.es.
Authority
The response has no authority records.
Additional
sun.rediris.es. 5 A 199.184.182.1
ns02.fccn.pt. 3 A 193.136.2.228
chico.rediris.es. 5 A 162.219.54.2
scsnms.switch.ch. 3 A 130.59.31.26
sun.rediris.es. 5 AAAA 2620:171:808:0:0:0:0:1
ns02.fccn.pt. 3 AAAA 2001:690:a80:4001:0:0:0:200
chico.rediris.es. 5 AAAA 2620:10a:80eb:0:0:0:0:2
scsnms.switch.ch. 3 AAAA 2001:620:0:ff:0:0:0:a7
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0