We pick a.root-servers.net, one of the 13 root servers (1), and ask it about www.fr and learn that fr is delegated to five name servers (2), so we ask d.ext.nic.fr where we learn that www.fr is delegated to three name servers, including ns1.nic.fr (3), so we ask that one and get the following answer:
Www.fr is a domain controlled by three domain name servers at nic.fr having a total of six IP numbers. All six of them are on different IP networks. Incoming mail for www.fr is handled by three mail servers also at nic.fr having a total of four IP numbers. Two mail servers have the same IP number. Some of them are on the same IP network. Www.fr has one IP number (192.134.4.49), but the reverse is eros5.nic.fr.
Three of the eleven domains that use the two mail servers mx4 and mx5.nic.fr together (but not mx3.nic.fr ), hereafter referred to as "mail server group 1", point to the two IP numbers 2001:660:3003:2::4:20 and 192.134.4.20 together.
