webserver01.sigla.com has no NS records.
NS records for this zone are defined at sigla.com.
NS records for this zone are defined at sigla.com.
Question and response
Question
dig webserver01.sigla.com. NS
Answer
The response has no answer records.
Authority
sigla.com. 900 SOA ns1.omeganet.it. awsdns-hostmaster.amazon.com. 1 7200 900 1209600 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0