mx2.dev.ficolo.net has no NS records.
NS records for this zone are defined at dev.ficolo.net.
NS records for this zone are defined at dev.ficolo.net.
Question and response
Question
dig mx2.dev.ficolo.net. NS
Answer
The response has no answer records.
Authority
dev.ficolo.net. 1751 SOA dns1.ficolo.net. hostmaster.ficolo.net. 2017020602 28800 7200 604800 86400
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0