ftp.insude.edu.do has no NS records.
NS records for this zone are defined at insude.edu.do.
NS records for this zone are defined at insude.edu.do.
Question and response
Question
dig ftp.insude.edu.do. NS
Answer
The response has no answer records.
Authority
insude.edu.do. 14400 SOA ns1.siteground.net. admins.siteground.com. 91 86400 7200 3600000 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0