Address Resolution Protocol (ARP)

Introduction

While end hosts may use IP addresses to communicate with each other, the underlying data link layer uses its own naming schemes. So, end host interfaces have unique data link layer addresses. In order to get data to a host, a mechanism for converting IP addresses to the underlying data link layer address is needed. This entails that all sending hosts must know the data link-layer address of their destination hosts in order to send them a packet.

For example, the figure below shows four hosts attached to the same LAN configured with IPv4 addresses in the 10.0.1.0/24 subnet and data link layer addresses represented as a single character. In this network, if host 10.0.1.22/24 wants to send an IPv4 packet to the host with address 10.0.1.8, it must know that the data link layer address of this host is C.