ftp.sentris.net has no NS records.
NS records for this zone are defined at sentris.net.
NS records for this zone are defined at sentris.net.
Question and response
Question
dig ftp.sentris.net. NS
Answer
The response has no answer records.
Authority
sentris.net. 86400 SOA ns.wahju.com. servers.sentris.com. 2020070508 3600 1800 1209600 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0