The first half of the address identifies the manufacturer of the plate and the second half the manufacturer determines a number that never used. Odom (2008, p.47). Still, according to Gouveia (2007, p 66) what normally it happens is that the computers, to if communicating between itself, always send address MAC for the net and alone later number IP (Internet Protocolo). The IP establishes a logical addressing, making possible that any destination is identified, facilitating its search. Furukawa (p 51). To facilitate the agreement, address IP is associated with the MAC of each host (net device), in the same way a computer name, or of any accessible resource in the net it is associated with an address IP. For the association of address MAC, that is of 48 bits, with address IP of 32 bits was defined a protocol that mapeia of dynamic form the MAC to the IP, this protocol is the ARP (Address Resolution Protocol? Protocol Resolution of Addresses). To eat (1996, P.
82) in supplies an idea to them for backwards of the dynamic conversion with the ARP: when one host ‘ ‘ A’ ‘ it wants to discover address IP, it transmits for diffusion a special package that addressee asks for host who answers with its physical address. All hosts, also the addressee, receive the request, but host destination only recognizes the package. To reduce costs with communications, the computers that use ARP keep one cache with mapping between physical addresses and IP? s, recently acquired, and thus does not need frequently to use ARP. Whenever a computer receives a reply ARP, it keeps in its cache address IP of the transmitter and its address of the corresponding hardware for successive research. To eat (1998, P. 83) However, as Odom (2008, 88), the designers of nets need to try to make with that the use of the net is simplest possible, therefore the using ones go to want in the maximum, if to remember the name of another computer with which they desire if to communicate, therefore they do not go to want to remember addresses IP?