ns4.layer6.net has no NS records.
NS records for this zone are defined at layer6.net.
NS records for this zone are defined at layer6.net.
Question and response
Question
dig ns4.layer6.net. NS
Answer
The response has no answer records.
Authority
layer6.net. 3600 SOA web-nl.itldc.com. mnt-by.itldc.com. 2019122186 10800 3600 604800 86400
Additional
. 0 OPT ; payload 1680, xrcode 0, version 0, flags 0