spf-a.aena.es has no NS records.
NS records for this zone are defined at aena.es.
NS records for this zone are defined at aena.es.
Question and response
Question
dig spf-a.aena.es. NS
Answer
The response has no answer records.
Authority
aena.es. 900 SOA dns6.aena.es. please_set_email.absolutely.nowhere. 869 10800 3600 2592000 900
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0