Describe the function of ARP (Address Resolution Protocol).

The Address Resolution Protocol (ARP) is a fundamental networking protocol used in Internet Protocol (IP) networks to map an IP address to a physical (MAC) address. It operates at the Link Layer of the OSI model and is essential for the proper functioning of Ethernet and other packet-switched networks.

Here's a breakdown of how ARP works:

1. IP to MAC Address Resolution:
   When a device on a local network wants to communicate with another device, it needs to know the MAC address of the target device. Devices use IP addresses to identify each other at the network layer, but at the data link layer, MAC addresses are used. ARP helps in resolving this mismatch.
2. ARP Request:
   If a device wants to find the MAC address corresponding to a specific IP address, it broadcasts an ARP request packet onto the local network. The packet contains the target IP address and the sender's MAC address.
3. ARP Reply:
   The device with the matching IP address responds to the ARP request with an ARP reply. This reply includes its MAC address. The sender, upon receiving the reply, updates its ARP cache, associating the IP address with the correct MAC address.
4. ARP Cache:
   Each device maintains an ARP cache or ARP table, which is a local mapping of IP addresses to MAC addresses. This cache helps in speeding up future communications by eliminating the need for repeated ARP broadcasts for known addresses.
5. Gratuitous ARP:
   A device may periodically send gratuitous ARP messages to announce its presence on the network or update other devices with its current MAC address.