What is Address Resolution Protocol (ARP)

What is Address Resolution Protocol (ARP)

Understanding the Basics of Communication Protocols

Sofwan A. Lawal's photo
Sofwan A. Lawal
·Aug 9, 2022·

4 min read

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Table of contents

  • What is ARP?
  • Why was ARP needed?
  • How Does the Address Resolution Protocol Work?
  • Why is ARP Important?
  • Differences between an ARP and a DHCP server
  • Conclusion

Computers require a common language in order to communicate with one another. We have communication protocols which are the guidelines that computers must go by when communicating. An aspiring network engineer may find it difficult to get started because there are so many distinct communication protocols available. The good news is that most of these networking terms are derived from common language. Therefore, knowing the fundamentals of ARP will offer you an advantage in practically every situation, regardless of what you intend to perform with your knowledge of networking.

What is ARP?

ARP stands for Address Resolution Protocol. It is an Internet Protocol that enables computers connected by a Local Area Network to recognise the hardware address of another device. A network address must be assigned to each device connected to a network. This address may be chosen statically or randomly from a pool of IP addresses. Once the machines on the network have their IP addresses, they must be able to find one another. This can be done over a local area network using ARP. ARP uses the Ethernet standard's built-in broadcasting feature to ask each device connected to the local area network (LAN) for the IP address that corresponds to a certain MAC address.

Why was ARP needed?

The difficulty with address resolution was obvious even before the TCP/IP protocol suite had even been fully developed. Even before Ethernet had been formally standardised as IEEE 802.3, a significant portion of the early development of IP was conducted on the then-emerging Ethernet local area networking technology. To enable communication over Ethernet networks, a method for mapping IP addresses to Ethernet addresses has to be established. The flexibility that comes from employing the dynamic resolution paradigm was something the IP designers wanted. They created the TCP/IP Address Resolution Protocol to achieve this (ARP). One of the early Internet RFCs currently in use, RFC 826, An Ethernet Address Resolution Protocol, released in 1982, has a description of this protocol.

How Does the Address Resolution Protocol Work?

When two computers are on the same network, they can use ARP to find each other and communicate. Here’s how it works:

  • First, one computer sends a broadcast message over the network looking for the hardware address of the other computer.
  • All computers on the network receive this message and simply ignore it if it does not apply to them.
  • The computer with the IP address that matches the hardware address of the message receives it and sends a reply.
  • The computer that sent the initial message receives the reply and stores the hardware address of the other computer in its network table.
  • It then sends a message to let the other computer know the table has been updated to include the new address.

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Why is ARP Important?

The ability for machines on the same network to find one another makes ARP crucial. This makes it possible for two computers to communicate even when they are using different protocols. For instance, a computer can transmit print jobs to a network printer that communicates via the Internet Printing Protocol (IPP), thanks to ARP.

Differences between an ARP and a DHCP server

It's often common to mistake ARP for DHCP (Dynamic Host Configuration Protocol).

  • ARP resolves IP addresses to MAC addresses and vice versa if you’re able to trace the network where the device is connected. ARP finds the Physical address of a device on the network, such as a WiFi router or printer, by knowing the device's IP address.
  • DHCP servers are Internet servers that assign IP addresses easily and quickly. These IP addresses are usually assigned from a pool of addresses that DHCP servers have been assigned.

Conclusion

You can see that the Address Resolution Protocol is a crucial component of computer networking, particularly on a Local Area Network. Even if they are utilising different protocols, it enables computers to locate one another and interact. As a backend engineer, Understanding ARP functions is crucial whether you're setting up a computer network or connecting a device to one in order to keep the network operating smoothly.

 
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