We pick j.root-servers.net, one of the 13 root servers (1), and ask it about l1virt.onet.pl and learn that pl is delegated to eight name servers (2), so we ask c-dns.pl where we learn that onet.pl is delegated to five name servers, including dns3.onet.pl (3), so we ask that one and get the following answer:
l1virt.onet.pl has one IP number (217.97.201.32), which also has a corresponding reverse pointer. Onet.pl is delegated to five domain name servers, however one extra name server is listed in the zone....