o2.ptr5243.codetwo.com has no CNAME records.
Question and response
Question
dig o2.ptr5243.codetwo.com. NS
Answer
The response has no answer records.
Authority
codetwo.com. 180 SOA ns10.digicertdns.com. dns.digicertdns.com. 2009010522 43200 3600 1209600 180
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0