mx01.isnic.is has no NS records.
NS records for this zone are defined at isnic.is.
NS records for this zone are defined at isnic.is.
Question and response
Question
dig mx01.isnic.is. NS
Answer
The response has no answer records.
Authority
isnic.is. 1800 SOA ht-secondary01.isnic.is. hostmaster.isnic.is. 1772290912 21600 7200 2419200 1800
Additional
. 0 OPT ; payload 1400, xrcode 0, version 0, flags 0