cluster3.convio.net has no CNAME records.
Question and response
Question
dig cluster3.convio.net. NS
Answer
The response has no answer records.
Authority
convio.net. 136 SOA dns1.convio.net. netadmin.convio.com. 2026021901 1800 300 1209600 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0