ns4.virtual1.com has no NS records.
NS records for this zone are defined at virtual1.com.
NS records for this zone are defined at virtual1.com.
Question and response
Question
dig ns4.virtual1.com. NS
Answer
The response has no answer records.
Authority
virtual1.com. 3600 SOA ns3.virtual1.com. hostmaster.virtual1.com. 2019041035 14400 1800 1209600 3600
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0