web21.avertis.net has no CNAME records.
Question and response
Question
dig web21.avertis.net. NS
Answer
The response has no answer records.
Authority
avertis.net. 534 SOA dns20.ovh.net. tech.ovh.net. 2026021800 86400 3600 3600000 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0