z.nessus.at has no CNAME records.
Question and response
Question
dig z.nessus.at. NS
Answer
The response has no answer records.
Authority
nessus.at. 5334 SOA ns1.nessus.at. domain-admin.nessus.at. 2025111702 3600 1800 604800 7200
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0