51.9.173.34.bc.googleusercontent.com has no CNAME records.
Question and response
Question
dig 51.9.173.34.bc.googleusercontent.com. NS
Answer
The response has no answer records.
Authority
googleusercontent.com. 60 SOA ns1.google.com. dns-admin.google.com. 877860005 900 900 1800 60
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0