pmm.zygo.nl has no NS records.
NS records for this zone are defined at zygo.nl.
NS records for this zone are defined at zygo.nl.
Question and response
Question
dig pmm.zygo.nl. NS
Answer
The response has no answer records.
Authority
zygo.nl. 86400 SOA auth01.dns.trueserver.nl. hostmaster.trueserver.nl. 2018102497 86400 3600 604800 86400
Additional
. 0 OPT ; payload 1400, xrcode 0, version 0, flags 0