ast.tuthost.com has no CNAME records.
Question and response
Question
dig ast.tuthost.com. NS
Answer
The response has no answer records.
Authority
tuthost.com. 3056 SOA ns1.tuthost.com. hostmaster.tuthost.com. 2025012000 3600 3600 1209600 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0