A computer communicates with other computers through network interfaces. In general, there is a network interface for each network card (for computers that have several network cards). A network card (Ethernet or wifi) has a mac address, which identifies the network card on the network. To operate a network card, you must configure the interface that corresponds to it. The if config command allows you to know the network configuration and configure the network by hand or in a script. On the internet, stations called hosts have IP addresses, which allow them to be identified, but a host can also often be designated by a host name or domain name (like google.Com). The DNS (domain name system) was designed to solve this problem, by offering a hierarchical model. Each machine (printer, terminal, server, etc.) connected to a network is assigned a small name. This name is unique within the domain to which it belongs. Thus, for the domains domain1.Com and domain2.Com, we can have two machines with similar or different names.