73.69.6.51.dyn.plus.net has no CNAME records.
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. 10800 SOA ns1.force9.net. hostmaster.force9.net. 2016041801 86400 8640 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0