ARP (Address Resolution
Protocol): IP works at network layer. IP address is a logical address. If a packet is to be delivered to a destination machine, its physical address (MAC address) needs to be known. ARP is a protocol, which enables a machine to obtain its MAC address from a know IP address.
RARP (Reverse Address Resolution Protocol): RARP is used to obtain IP address from a known MAC address.
BootP (Bootstrap Protocol): When a diskless workstation is powered on, it broadcasts a BootP request on the network. A BootP server responds with its IP address, Default gateway, etc.