What is ARP?

The Address Resolution Protocol (ARP) is an Internet layer protocol that helps TCP/IP network components to find other devices in the same broadcast domain.
 
The purpose of the ARP protocol is to find out the mac address of the device having a specific IP Address. If the device is present in the same broadcast domain then the device mac address is found. If the device is present in a different broadcast domain, then ARP protocol will request for gateway device MAC address.
 

Why ARP?

When two ethernet device wants to talk to each other at the data link layer,  then they need to know each other’s mac address. ARP protocol helps the ethernet device to get the other ethernet device mac address.

How ARP Works?

ARP has two types of packet.

  • ARP Request
  • ARP Reply

arp request arp reply 1

With the help of two packets, the MAC address will be calculated for the given IP Address. For better clarity, I will explain the ARP protocol through lab exercise.

Disclaimer: GNS3 software is used for lab simulation and Wireshark is used for packet capture.

USE CASE 1: ARP between two nodes

 

arp-two-node-example