_sip.iristransport.com has no NS records.
NS records for this zone are defined at iristransport.com.
NS records for this zone are defined at iristransport.com.
Question and response
Question
dig _sip.iristransport.com. NS
Answer
The response has no answer records.
Authority
iristransport.com. 900 SOA ns1.iristransport.net. hostmaster.iristransport.net. 2023111400 10800 15 604800 10800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0