fb-mx.LF.net has no CNAME records.
Question and response
Question
dig fb-mx.LF.net. NS
Answer
The response has no answer records.
Authority
lf.net. 3600 SOA dns1.lf.net. hostmaster.lf.net. 2026030600 86400 10800 604800 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0