We pick k.root-servers.net, one of the 13 root servers (1), and ask it about tucows.com.pl and learn that pl is delegated to eight name servers (2), so we ask f-dns.pl where we learn that tucows.com.pl is delegated to two name servers, including ns2.aftermarket.pl (3), so we ask that one and get the following answer:
At least one of them use the two name servers ns1 and ns2.dropped.pl together, hereafter referred to as "name server group 1", (example: czapnictwo.pl ).
The IP number 212.91.7.33
There are several thousand of host names that point to the IP number 212.91.7.33.
At least one of them use the two name servers ns1 and ns2.aftermarket.pl together, hereafter referred to as "name server group 2", (example: trudne.com ).
The two IP numbers 212.91.6.58 and 212.91.7.33 together
There are several thousand of host names that point to IP group 1.