Question

What is the actual purpose of the Address Resolution Protocol? Specifically, what identifier does it connect with which other identifier?

Answer 1

IP address is used to send/receive messages from one host to another, but the real communication happens over the MAC ddress
Address resolution protocol is used to find MAC address of host from it's IP address.

ARP is used in the situation below:
SITUATION-1: The sender is a host in a network & wants to send a packet to another host on the same network as the sender. ARP is used here to find another host physical address in same network
SITUATION-2: The sender is a host & wants to send a packet to another host on another network.
Sender looks at its routing table and find the IP address of the next hop (router) for this destination.
ARP is used to find the router’s physical address
SITUATION-3: the sender is a router & received a datagram destined for a host on another network.
Router check its routing table and find the IP address of the next router.
ARP is used here
SITUATION-4: If sender is a router that .has received a datagram destined to a a host in the same network.
ARP is used here to find this host’s physical address.