What Is Address Resolution Protocol?

Written by Coursera Staff • Updated on

Learn about the address resolution protocol and how it connects a computer's IP address to a MAC address within a local area network.

[Featured Image] Two employees discuss Address Resolution Protocol in the office.

By facilitating the connection between the internet protocol (IP) address and media access control (MAC) address, the address resolution protocol (ARP) enables communication between devices connected to a local area network. This allows for the transfer of data back and forth between software and the devices within a network. The MAC address is also known as the physical address of the device or machine.

How does the address resolution protocol work?

When transferring data from devices through the network and to a host machine, the data first arrives at a gateway that supports the flow of data throughout different networks. From there, the gateway relies on the ARP to find a matching IP and MAC address. This information exists within the ARP cache or ARP cache table.

After confirming the matching addresses, the data is free to travel through the network to the correct device. However, if a device is unable to find the matching IP and MAC addresses in the ARP cache, then an ARP request initiates. An ARP request allows devices to establish communication with one another, resulting in a new addition to the ARP cache table.

Due to the small size of the ARP cache, removing addresses from the cache often occurs to ensure ample space for new addresses, as well as help mitigate the risk of cyber attackers who could attempt to steal IP addresses.

Types of address resolution protocols

Here are the four different types of address resolution protocols and the details that make each unique:

  • Proxy ARP: During a proxy ARP, a proxy device responds to the request for the IP address of a device that doesn’t belong to the local area network. Rather than sending the MAC address of the targeted device, the proxy device shares its own MAC address instead.

  • Gratuitous ARP: Instead of responding to an ARP request, a gratuitous ARP response occurs to help host devices update the ARP cache with IP and MAC addresses found throughout the entire network.

  • Reverse ARP: In cases where systems or networks don’t have the memory to store their own IP address, reverse ARP sends an IP address instead of a MAC address, allowing the system to discover its IP address and enabling it to communicate within the network.

  • Inverse ARP: A traditional access protocol uses an IP address to locate a MAC address. However, an inverse ARP performs oppositely, translating MAC addresses to IP addresses. 

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