b.isi.edu has no NS records.
NS records for this zone are defined at isi.edu.
NS records for this zone are defined at isi.edu.
Question and response
Question
dig b.isi.edu. NS
Answer
The response has no answer records.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0