We pick g.root-servers.net, one of the 13 root servers (1), and ask it about saude.nl and learn that nl is delegated to eight name servers (2), so we ask nl1.dnsnode.net where we learn that saude.nl is delegated to three name servers, including nsauth01.solcon.nl (3), so we ask that one and get the following answer:
Saude.nl is a domain controlled by three domain name servers at solcon.nl having a total of six IP numbers. Some of them are on the same IP network. Incoming mail for saude.nl is handled by four mail servers also at solcon.nl having a total of eight IP numbers. Some of them are on the same IP network.
All of the more than two thousand domains that use the primary name server nsauth01.solcon.nl use name server group 1 (example: holmwoods.eu, zonberg.com and teamwijs.com ). Worth noting is that half of the domains that use name server group 1 use the primary name server nsauth01.solcon.nl.
The three name servers nsauth01, nsauth02 and nsauth03.solcon.nl together
There are several thousand of domains that use name server group 1.