The primary purpose of the ARP or the Address Resolution Protocol is the association of an Internet Protocol address to the address of a physical machine that is part of a local network. As of 2014, IP addresses can range from 32 bits to 48 bits in length.
IP addresses that are generated on IP Version 4 are 32 bits long and, as of 2014, are one of the most commonly used IP levels. IP addresses that are used in an Ethernet local area network are typically 48 bits long when it is associated with devices attached to it. The address of the physical machine is known as a MAC, or Media Access Control, address. The ARP then generates a cache file that contains information correlating a MAC address with an IP address. The protocol is also responsible for address conversion between the MAC and IP addresses.
Each type of local area network typically has distinct protocol details. The ARP was developed to create independent Requests for Comments commands for various networks, such as ATM, HIPPI or Ethernet.
There is also a reverse version of the ARP which is called the RARP. This protocol is used by host machines that have no information regarding their IP addresses and allows them to request the info from the ARP cache file.