Address Resolution Protocol

Address Resolution Protocol (ARP) is a critical Layer 2 protocol of the Internet Protocol (IP) suite that translates IP addresses to Media Access Control (MAC) addresses (IP – MAC). Playing an indispensable role in enabling network connectivity, ARP tool enables discovering and mapping the hardware address of a device on a local network to its IP addresses. Address Resolution Protocol in computer networks is essential for resolving and associating IP addresses with corresponding MAC addresses, ensuring efficient communication between devices.

On this page, we will explain the basics of ARP, including:

What is Address Resolution Protocol (ARP)?

Resolving the data link layer IP addresses to the physical layer MAC addresses, ARP protocol is used by several network components to determine the target network device based on the specified IP. The Address Resolution Protocol can be used to discover the MAC address of a device on the same network as the sender. While it aids in resolving physical layer addresses, ARP operates at Layer 2 of the Open Systems Interconnection (OSI) model, which is the data link or network layer.

How ARP works?

Address Resolution Protocol - ManageEngine OpUtils

IP – MAC associated details form the basis of enabling network communication between different components. When a network device requires to send a data packet to a target device, it needs the MAC address of the target device.

The device first checks its ARP cache to check if it has the MAC address of the target device.

If the IP – MAC association detail of the target device is found, the device uses this detail to establish communication with the target device.

If the IP – MAC association detail of the target device is not found, the device should first identify the MAC address of the target device. To do this:

  • The device that wishes to establish communication broadcasts an ARP request packet in the network, requesting the MAC address of the device with the specified IP address.
  • The ARP request packet contains the IP address of the destination device and the MAC address of the sending device.
  • On receiving a ARP request broadcast packet, network devices compare the IP address in the packet with their own IP address.
  • The device whose IP address matches with the IP in the ARP request then sends an ARP reply packet to the requesting device. The ARP reply packet contains the MAC address of the device that sent the reply.
  • The requesting device, upon receiving the ARP reply packet with the IP – MAC association detail, uses this information to send data directly to the target device.

Hence, ARP software is instrumental in facilitating the translation of IP addresses to MAC addresses and optimizing communication among devices within the network.

ARP cache and its role in IP address management (IPAM)

As discussed earlier, network devices rely on their ARP cache to identify IP – MAC associations and forward data packets. Each network device, including routers and switches, maintains an ARP cache that logs a list of recent ARP requests and identified IP – MAC associations in their network.

The ARP caches aid in speeding up future ARP lookups and ARP requests by minimizing the need for ARP broadcast on the network for frequently communicating devices. An ARP cache entry typically contains the IP address and MAC address of a device, along with a timestamp of when the entry was last used. With networks changing dynamically, and to avoid stale or outdated entries, the ARP cache is to be periodically cleared. In summary, ARP in networks enhances efficiency by utilizing ARP caches to expedite future ARP lookups and requests, minimizing the reliance on broadcast traffic.


ARP is not a platform but a rather a protocol used in networking. Here are a few platforms that use ARP in networking:

  • Network switches
  • Rogue detection and security tools
  • Network monitoring tools
  • IP address management tools

Let's look at how an IP address management solution uses ARP(Address Resolution Protocol):

An effective IP address manager relies on tracking up-to-date ARP caches or tables in the network. This is critical for maintaining efficient network operations, since relying on stale ARP caches can result in issues such as slow network performance. Thus, here are few ARP solutions network admins need to ensure:

  • The ARP caches are periodically cleared or updated with the latest information.
  • The IPAM tool deployed is configured to monitor reliable ARP data sources to collect and update IP address details in real time.

By integrating an IP address management tool with ARP cache management, network admins can have a more complete picture of the network layer and its IP – MAC associations. IPAM solutions can provide real-time visibility into the ARP cache, enabling administrators to quickly identify and resolve issues.

Also, leveraging an ARP cache to gain insights into the real-time IP – MAC associations in the network can help admins avoid issues such as IP address conflicts and subnet over utilization.

ARP poisoning: The enabler of rogue device attacks

Address Resolution Protocol (ARP) Software - ManageEngine OpUtils

ARP cache poisoning, also known as ARP spoofing or ARP poisoning, is a technique used to intercept the network traffic by manipulating the ARP cache of a targeted device. To execute ARP poisoning, the attacker, on detecting an ARP request broadcast, sends an ARP reply with their MAC address, under the pretext that the MAC address is associated with the requested IP address. The target device, on receiving this ARP reply, updates its ARP cache with the malicious IP – MAC association detail. The targeted device will then send data packets to the attacker's MAC address, allowing the attacker to intercept and modify the packets.

ARP poisoning often enables further complex attacks. Networks supporting BYOD policies, IoT, and shadow IT should be precautious, since rogue devices can easily carry out network attacks on these technologies using ARP poisoning.

Rogue devices, which enter the network under the pretext of being a trusted user device, can use ARP poisoning to intercept network traffic and run several complex attacks including man in the middle attacks, data theft, and malware ingestion.

Also, by using ARP cache poisoning, an attacker can redirect network traffic to a rogue device that they control, instead of allowing the traffic to reach its intended destination. This rogue device can then be used to launch a variety of attacks, such as eavesdropping, data theft, and denial-of-service attacks.

For instance, an attacker can use ARP poisoning to intercept and modify network traffic between a client device and a server. The attacker can redirect the traffic to a rogue device they control by launching a man-in-the-middle attack. The client device and the server is unaware of this manipulated traffic and can run confidential data requests through the rogue device.

Given its serious threat to network integrity and security, identifying and preventing ARP spoofing is critical. Network admins must deploy a reliable ARP spoofing detection and prevention tool to spot unusual ARP activity and mitigate ARP spoofing.

Stay in the know of your IP address space with OpUtils

OpUtils is a comprehensive IP address management solution that offers advanced features to help you efficiently manage your network address space. With OpUtils' advanced IP scanning and IP tracking of your network's ARP logs, you can easily manage your IP addresses, subnets, and DHCP server scopes in real time, and monitor your network for potential issues.

Address Resolution Protocol Tool in Computer Networks - ManageEngine OpUtils

It's rogue detection and prevention module easily detects and removes rogue devices, preventing them from accessing your network. Along with throttling malicious access to your network, OpUtils enables you to detect ARP spoofing attacks in real-time and receive alerts that aid in instant ARP poisoning mitigation.

New to OpUtils? Download a free, 30-day trial or schedule a personalized demo with our product experts to learn more.

Address Resolution Protocol (ARP) FAQs

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