ARP Process

 THE ARP PROCESS

when it comes to arp process in network world we often get confused who will initiate arp process, Arp work on Which protocol and so on.

In this blog will cover some of the ARP questions with practical examples.

ARP - Adress resolution protocol.

As we can see the name itself says adress resolution protocol but now the question comes which address.

To Answer this we need to understand few things in network work we usually have 2 type of address
1. IP Address.
2. Mac Address.

now understand in what scenerio we run IP address resolution and what protocol we use, this is very basic.
When we type any fqdn in our browser it need to be resolved with some ip and for this type of resolution we use DNS resolution services.

As we Understand we will use DNS for IP address resolution now comes a MAC resolution process.

Before we understand how arp process worls first understand why Mac resolution required.

PC-1 will never get to know PC to MAC address without ARP process and if mac address is not available in destination layer2 header switch will always flow traffic.

For this ARP process was designed so traffic should go to specific destination.

Based on Above diagram we see IP and mac details of both the devices. 

Now will understand actual arp process and who will start ARP in this scenerio.

PC1 Initiate Traffic with PC2 , In this case source is PC 1 and destination is PC2.

Assuming PC 1 is initiating traffic based on IP address and not based on FQDN as of now.

When PC-1 initiate Traffic initially its Header address will have following details.

Source ip - PC 1 Spurce 

Destination IP - PC-2 IP 

Source MAC - PC-1 MAC

Destination MAC Broadcast mac.

This is a ARP request initiate by PC-1 before he sends ICMP request.

This ARP request will go to Switch.

Switch will see he received Traffic with PC 1 Source mac and destination as Broadcast mac.Switch will fload this traffic now.

PC-2 will receive this traffic and after reading Header he understand this is a arp request and asking his mac.

PC-2 will send ARP reply.

ARP reply Packet.

Source IP - PC2 IP

Destination IP - PC-1 IP

Source MAC - PC-2 MAC

Destination MAC - PC-1 MAC.

this details will be send to Switch and when switch receives this details from PC-2 it will again store PC-2 MAC on particular port and forward this frame to PC1.

PC1 Receives ARP reply and ARP process Completes.

NOW after Arp process PC sends ICMP packet.