Five types of ARP has been defined as following:
- Simple ARP
- Proxy ARP
- Gratuitous ARP
- RARP (Reverse ARP)
- Inverse ARP
Simple ARP is very common and it is used to get the MAC address of the destination IP. When source machine wants to send a packet to destination machine, it need MAC address of destination machine. If source machine sent the packet to destination machine successfully then it updates its arp (address resolution protocol) table and you can easily check the arp table by triggering the command like "arp -n"
"Proxy ARP" is used when source machine and destination machines belong to different network. In this case router comes into picture and source machine sends packet to router and router then forward packet to destination machine by looking into routing table.
Gratuitous ARP is used to update MAC and IP address mapping entries in all machines of the network. This is also used to detect duplicate IP address assignment within the network.
RARP protocol is used to get the IP address from the MAC address. It is just reserve process of ARP process that's why it is known as RARP. Normally IP address configuration of the machine is stored in local disk and when system is started, it reads from the configuration file and configures the same in interface cards. There might be the case when system does not have local disk and storage in that case each time system needs to fetch the IP address from other server. To do so, system uses RARP protocol to get the IP address from the MAC address.
Inverse ARP is used to resolve layer 2 to layer 3 information in frame relay. Layer 2 is DLCI and is used to get the IP address of router. I don't have more information on this. Please refer RFC 2390.
