ARP stands for Address Resolution Protocol and is used to map IP addresses to MAC addresses on a local network. There are different types of ARP including Proxy ARP, Gratuitous ARP, Reverse ARP, and Inverse ARP. Proxy ARP allows a router to respond to ARP requests and map the router's MAC address to the target IP address. Gratuitous ARP helps identify duplicate IP addresses on a network. Reverse ARP allows a client to request its IPv4 address from a router table.