An ARP (Address Resolution Protocol) packet includes several fields necessary for network devices to determine the mapping of an IP address to a physical machine address. These fields include the Source Hardware Address, which indicates the physical address of the sender; the Hardware Type, which specifies the type of network (e.g., Ethernet) being used; the Source Protocol Address, which contains the IP address of the sender; and the Operation Code, which specifies the type of ARP message being sent (either a request or a response).