What is ARP(Address Resolution Protocol)?

It is used to resolve IP addresses to MAC address(MAC Address is the physical address of the device)

When ever a device needs to communicate with another device on the same network, it needs the MAC address for that device, and so, devices use ARP to aqcuire the MAC address for that device.

1. An IP address is used to locate a device on the network

2. The MAC address identifies the actual device

3. In order to find the MAC address, the computer will look at its internal list called ARP cache, to see if the other computer IP address already has a matching MAC address, and if it does it will use that. 

4. If it does't find it,then it will send out a broadcast message to everyone on the network asking every device "which computer has this IP address, and what is your MAC address?"

5. Next the computer with the matching ip address will respond back with its MAC address, and now they can communicate!, and it will also store the MAC address in the ARP cache aswell as the IP address so that the next time they need to communicate it will just check the cache!

Things to Note

   1. Dynamic ARP entries are not permanent, they are removed periodically so that the cache does't get filled up with too many entries

   2. A static entry is when someone manually enters an IP to MAC address using the ARP command utility, and you set this when you know that two devices are constantly communicating with each other