73.69.6.51.dyn.plus.net has no NS records.
NS records for this zone are defined at 6.51.dyn.plus.net.
NS records for this zone are defined at 6.51.dyn.plus.net.
Question and response
Question
dig 73.69.6.51.dyn.plus.net. NS
Answer
The response has no answer records.
Authority
6.51.dyn.plus.net. 43200 SOA ns1.force9.net. hostmaster.force9.net. 2016041801 86400 8640 1209600 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0