In simple terms, the MAC address is the hardware address. Any hardware with network capability usually would have an address hard-coded into it's network interface. The uniquely identifies the hardware on a network.
What then is the role of the Address Resolution Protocol (ARP)
On a network, all devices need to be assigned an IP address (statically or dynamically). There is therefore a need to have a mapping between an assigned IP (on the network) and the MAC address of a device on the network. This mapping is very crucial in the Internet Protocol (IP) suite.
The Address Resolution Protocol is responsible for discovering the MAC address associated with an IP address on a network.
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