Apex domains cannot have CNAME records.
Question and response
Question
dig gva.es. NS
Answer
gva.es. 5 NS tirant2.gva.es.
gva.es. 5 NS ninot2.gva.es.
gva.es. 5 NS ninot.gva.es.
gva.es. 5 NS tirant.gva.es.
Authority
The response has no authority records.
Additional
ninot.gva.es. 5 A 195.77.16.50
ninot2.gva.es. 5 A 193.144.127.33
tirant.gva.es. 5 A 193.144.127.68
tirant2.gva.es. 5 A 193.145.200.15
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0