sasl6.shellrent.com has no CNAME records.
Question and response
Question
dig sasl6.shellrent.com. NS
Answer
The response has no answer records.
Authority
shellrent.com. 1741 SOA ada.ns.cloudflare.com. dns.cloudflare.com. 2397345467 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0