mx101.softlayer.com has no NS records.
NS records for this zone are defined at softlayer.com.
NS records for this zone are defined at softlayer.com.
Question and response
Question
dig mx101.softlayer.com. NS
Answer
The response has no answer records.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1280, xrcode 0, version 0, flags 0