ns3.exoscale.net has no CNAME records.
Question and response
Question
dig ns3.exoscale.net. NS
Answer
The response has no answer records.
Authority
exoscale.net. 77 SOA ns2.exoscale.net. hostmaster.exoscale.net. 1389488509 7200 1800 2419200 300
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0