What is ARP Protocol and how does it work?

Friends, in this post today, we will know what is ARP Protocol and how does it work? The ARP-Address Resolution Protocol is a communication protocol used to search for Link-Layer Addresses, such as to locate a device's MAC address from an IP address.


It is used when a device wants to communicate with another device on the Local Network. For example, when a Sender in a Network wants to communicate with a Receiver, the Sender first checks his ARP Cache. Sender checks whether the Receiver's MAC address already exists in ARP Cache? If the MAC address of the Receiver is already present in the ARP Cache, then the sender will communicate with the Receiver using that MAC Address.
What is ARP Protocol and how does it work?


What is ARP Protocol and how does it work?


Most computer programs/applications use Logical address (IP address) to send/receive messages, although the actual communication is from Physical Address (MAC address) Layer 2 of the OSI model. Therefore our mission is to get the Destination MAC Address address which helps in communicating with other devices. This is where ARP does its work. Its functionality is to translate IP addresses into physical addresses. The ARP protocol is one of the most important protocols for the network layer in the OSI model.

Note: The ARP hardware address, also known as the Media Access Control (MAC) address, locates the host with its known IP address.

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Imagine that a device wants to communicate with another on the Internet. What does ARP do? Whether it broadcasts a packet for all devices in the source network. Open the header of the data link layer from the network's Device Protocol data unit (PDU), called a frame, and transfer the packet to the Network Layer (layer 3 of OSI), where the network ID of the packet is the destination IP's. is validated with the network ID. If the Network ID and Destination IP's network ID match, it responds to the source with the Destination's Mac Address. Otherwise, the packet reaches the gateway of the network and transmits the packet to the devices it is connected to and validates their network ID

The above process continues until the second last network device en route to reaching Destination, where it becomes valid and the ARP, in turn, reacts with the Destination MAC Address.

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Important Terms related to ARP

  1. ARP Cache: After Resolve MAC Address, ARP stores that source in a table.
  2. ARP Cache Timeout: Indicates the time for which MAC addresses can reside in the ARP cache.
  3. ARP request: This is nothing but broadcasting a packet over the network to validate whether we have arrived at the destination MAC address.
  • ARP request packet contains:
  • The physical address of the sender.
  • The IP address of the sender.
  • The physical address of the receiver is 0s.
  • The IP address of the receiver

Cases when ARP is used:


CASE-1: Sender is a Host and wants to send a packet to another host of the same network.

  • Use ARP to find another host’s physical address
CASE-2: Sender is a host and wants to send a packet to another host on another network.
  • The sender looks at its routing table.
  • Find the IP address of the next-hop (router) for this destination.
  • Use ARP to find the router’s physical address

CASE-3: Sender is a router and retrieves data from another network host.

  • The router checks its routing table.
  • Find the IP address of the next router.
  • Use ARP to find the next router's physical address.

CASE-4: Sender is a router that has received data from one of the hosts in the same network. Use ARP to find this host’s physical address.

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Conclusion

From today's post, we learned what the ARP Protocol is and how it works? What are the important terms related to ARP and what are the cases where the ARP protocol is used.

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