We pick c.root-servers.net, one of the 13 root servers (1), and ask it about a-dns.at and learn that at is delegated to eight name servers (2), so we ask d.ns.at where we learn that a-dns.at is delegated to four name servers, including a.ns14.net (3), so we ask that one and get the following answer:
A-dns.at is a domain controlled by four domain name servers at ns14.net having a total of seven IP numbers. All seven of them are on different IP networks. Incoming mail for a-dns.at is handled by one mail server at a-dns.at themselves. A-dns.at has one IP number (85.236.44.181), but the reverse is a-host.at.
A-dns.at is hosted on a server in Germany even though the hostname implies Austria.
Which servers does a-dns.at use?
A-dns.at uses the primary name server a.ns14.net, the four name servers a, b, c and d.ns14.net together, hereafter referred to as "name server group 1", the IPv4 number 85.236.44.181 only and the primary mail server mail.a-dns.at.
The primary name server a.ns14.net only
There are several thousand of domains that use the primary name server a.ns14.net.
Four percent of them use the two name servers a and b.ns14.net together (but neither c nor d.ns14.net ), hereafter referred to as "name server group 2", (example: aloe-vera-4ever.de, ifb-pirna.de and fbl-vg.de ). Worth noting is that all of the domains that use name server group 2 use the primary name server a.ns14.net.
The four name servers a, b, c and d.ns14.net together
There are several thousand of domains that use name server group 1.