a.nic.ruhr has no NS records.
NS records for this zone are defined at nic.ruhr.
NS records for this zone are defined at nic.ruhr.
Question and response
Question
dig a.nic.ruhr. NS
Answer
The response has no answer records.
Authority
nic.ruhr. 3600 SOA ns0.centralnic-dns.com. hostmaster.centralnic-dns.com. 1574704050 86400 7200 3600000 172800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0