o1.ptr3816.codetwo.com has no CNAME records.
Question and response
Question
dig o1.ptr3816.codetwo.com. NS
Answer
The response has no answer records.
Authority
codetwo.com. 48 SOA ns10.digicertdns.com. dns.digicertdns.com. 2009010523 43200 3600 1209600 180
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0