ns2.servidor-dns.com has no CNAME records.
Question and response
Question
dig ns2.servidor-dns.com. NS
Answer
The response has no answer records.
Authority
servidor-dns.com. 2945 SOA ns2.servidor-dns.com. sistemas.ecomputer.es. 2026020601 10800 3600 1209600 10800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0