unknown.volia.net has no CNAME records.
Question and response
Question
dig unknown.volia.net. NS
Answer
The response has no answer records.
Authority
volia.net. 1800 SOA ns1.voliacable.com. hostmaster.volia.com. 2026021800 43200 3600 1814400 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0