The pieces of information are exchanged from one source to another via messages or signals. Computer software and applications mostly use IP addresses to send these messages. IP addresses are the logical address to send the messages. But the actual communication between the systems happens over physical addresses that are generally known as MAC Addresses. These physical addresses are established over the local area network(LAN). The MAC Address is the second layer of the Open Systems Interconnection model (OSI model). This is the place where the role of the ARP protocol applies. ARP stands for Address Resolution Protocol that maps the IP address to the MAC address. Read on more to get the full information on how it works. 

In this article let us look at:

  1. What is Address Resolution Protocol?
  2. How does ARP Work?
  3. Types of ARP
  4. Why is ARP needed?
  5. Address Resolution Protocol Spoofing

1. What is ARP (Address Resolution Protocol)?

ARP is basically a communication protocol that is used to find the MAC Address of a device from the available IP address. Know What is ARP Protocol from the definition of RFC 826, as a protocol that is used to uncover the 2nd layered information that is associated with the internet layer addresses. The answer to what is Address resolution protocol is that it basically is a request and response protocol, where one device requests a piece of information and another device provides it over a LAN network.

It essentially translates the 32-bit addresses used by Ip addresses to 48-bit addresses generally used by MAC addresses and vice versa for the information exchange. You can also ask what are two features of arp. The answer to it will be the mapping of the addresses and helps to send and receive ARP messages.   

2. How does ARP Work?

The working of the address resolution protocol explained in a brief way as follows: 

  1. When a source device needs to connect with another device, the source Device checks its Address Resolution Protocol (ARP) store to find the MAC address of the destination device. The purpose of arp here is to search for the MAC address when the mac address is available and is transferred, the transfer of packets of information takes place. 
  2. When the Mac address of the destination device is not present, the source device broadcasts ARP requests to all the network devices present in the LAN. Each device, in turn, compares the target protocol address, i.e, the IPv4 Address of the destination device with its own protocol address. 
  3. If any of the devices find a match to their Ipv4 address to the targeted address, it generates an ARP reply message to the source. The device then uses the sender’s main IP and hardware address from the request message processes it and uses the values to the targeted IP and hardware address to reply messages.
  4. The destination device then updates its ARP cache and sends the unicast message reply to the source device. The Source device, on receiving the reply, process the ARP reply and saves the destination’s Hardware address as the layer 2 address for it.   
  5. The Source device then updates the Sender device’s hardware address and Protocol address received in the ARP reply in its own(source device) ARP cache. This is Now the packets are sent by the source as it knows the destination’s MAC address. 

From this, you can understand How ARP works in detail.

3. Types of ARP

There are four types of ARP: 

  1. Proxy ARP
  2. Reverse ARP (RARP)
  3. Gratuitous ARP
  4. Inverse ARP

The same is being discussed in detail as below:

Proxy ARP: Proxy ARP is a system that answers the ARP requests on the behalf of another system. When the request is sent by a system outside from the host’s network, the router acts as a gateway to send the packets outside the networks to their destinations. 

Reverse ARP (RARP): Reverse ARP meaning is a convention utilized by the customer framework in LAN to demand its IPv4 address from the ARP gateway router table. A table is made by the organization manager in the gateway-router that is utilized to discover the MAC address to the relating IP address.

Gratuitous ARP: An ARP request that helps in identifying duplicate IP addresses will be proper The Gratuitous ARP definition. It answers the question, what is the function of arp. It is a request from the broadcast to get the router’s IP address. It is used when an end system has an IP address but wishes to defend its MAC address from the LAor to check if the IP address is not used by any other node or system. 

Inverse ARP: Inverse ARP is a protocol that functions opposite to the ARP. It is used to find the Ip addresses of the systems over LAN from its MAC addresses. It is mostly used in ATM networks, or in frame relays, where level 3 data are acquired from the level 2 data. 

4. Why is ARP needed?

Devices in a Local Area Network(LAN) communicate with the ethernet addresses and not Ip addresses. The devices are not configured to allow destination devices within the same network to connect with the IP address. Any device will not have an IP address when it is not connected to the internet. In that case, the network has to use MAC addresses for communication.

When any needs to communicate with any other device in the over same network, it has to know the MAC address of the network interface of the destination device. If the source device knows the MAC address of the destination device, the communication between them can be unicast. The purpose and need of the ARP are to get the MAC address of the device. 

5. Address Resolution Protocol Spoofing

The LAN must be aware of ARP spoofing, where a hacker provides a false ARP protocol message and hacks the IP address of the devices within the network. It can lead to a serious loss of information and loss to enterprises. It can be avoided using some prevention techniques like Packet filtering, Use spoofing detection software, Use cryptographic network protocols, etc.

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