ip4.spf.routit.net has no NS records.
NS records for this zone are defined at spf.routit.net.
NS records for this zone are defined at spf.routit.net.
Question and response
Question
dig ip4.spf.routit.net. NS
Answer
The response has no answer records.
Authority
spf.routit.net. 900 SOA auth01-peer.ib.routit.net. noc.routit.nl. 5 1800 900 604800 900
Additional
. 0 OPT ; payload 1220, xrcode 0, version 0, flags 0