ARP Header and ARP Types

ARP (Address Resolution Protocol)

• L2 layer protocol, it is encapsulated in Ethernet-II frame 
• It use to resolve the L2 mac address using L3 ip address
• Arp cache maintains a correlation between MAC and IP address.

Types of ARP:

>> RARP

>> GARP
>> Proxy ARP

RARP - Reverse ARP

Before DHCP, RARP is used. RARP provides only the IP Address, but DHCP provides ip address along with 255 parameters.

GARP - Gratuitous ARP

• It is used to avoid IP Address conflict, where the source and target ip will be same
• The PC will broadcast an ARP request, and checks whether the received ip address is already in use by some other PC in the network.
• It is used in high availability protocols like VRRP (Virtual Router Redundancy Protocol)

Proxy ARP - Duplicate Gateway.

When the source and the destination are in the same network but different subnet, then the default gateway will provide its own MAC Address on behalf of the destination.