What is arp protocol ?
The ARP full form is Address Resolution Protocol. From full form says that the protocol is to resolve the destination address of a network packet. To understand the purpose of ARP protocol , we need to understand the message routing over internet or IP network. For example , if you are using the computer which is connected to the LAN over wifi router. Router assigns an internal or LAN IP address (e.g 192.168.1.4) to the computer connected to LAN via DHCP (may be a static ip as well). There might be other computers also connected to the wifi router, all gets and IP address. You can consider a connection between computer and wifi router as a communication link. So there may be multiple links, number of links depends on the connected devices to the router. If you browse a website from the web browser. The request is sent to the router and in response router sends the request to the public server , hosting the website. When response comes , router knows the IP address of your LAN computer , but do not know on which device to send. Here comes the ARP protocol. From ARP , router gets the physical address of the device or computer on LAN. Router sends the response to the device to which the message needs to deliver.
From above example , it is clear what is the role of ARP in computer networks. Now how the translation is done we will discuss. When sending device needs to send a message , it broadcast the ARP request with the destination ip address. All devices over LAN gets the request. But the device which matches the self IP address with the address in ARP request. Only sends ARP response back to the sending device with its own MAC address.
In computer network , there are various layers of protocols. Each layer have addressing for communication over network. ARP is the protocol which works as layer 2 of OSI model. Means ARP works on data link layer. It have interface with the network layer , which initiates the ARP request.