Understanding ARP – A Guide to the Different Types of ARP

ARP enables communication between devices on the same local area network (LAN). It functions at the data link layer of the OSI model.

ARP links a computer’s ever-changing Internet Protocol (IP) address to its fixed media access control (MAC) address. Without ARP, computers would not be able to communicate with one another.

Type 1

What are the types of ARP? Over the local area network, the ARP protocol enables network devices to translate IP addresses to Media Access Control (MAC) addresses. It is an essential component of computer networking, making communication easier for devices on the same LAN. However, it also introduces several security risks, such as ARP spoofing, which can lead to man-in-the-middle attacks.

When an ARP packet is sent on the LAN, it first checks the ARP cache table to see if a MAC-to-IP mapping is already present. If it does not, it sends an ARP request to the device’s MAC address which needs to know the IP address. The device that knows the IP address responds with its MAC address, returning the ARP reply.

As you can imagine, this process is vital for the efficiency of the LAN and ensures that all hosts have a unique IP address. The ARP protocol was not designed with security in mind and did not verify that the MAC address of the responding device was valid. Cybercriminals can exploit this weakness to conduct ARP spoofing attacks, which can cause data corruption. Therefore, it is vital to implement ARP security measures on your network. For example, consider using DHCP to assign dynamic IP addresses to each network host instead of manually configuring them.

Type 2

When a device in a LAN network wants to connect with another, it first consults its ARP cache. It is a table that contains mappings of IP addresses to MAC addresses, and it lets the device determine if the other device has the same hardware address. If it does, the device can insert the destination MAC address into the layer-2 frame and send it off.

However, if the ARP cache doesn’t have a matching entry, the host sends an ARP request to its neighbors. A router will respond with its own MAC address, and the original device will assume that the responding device is the destination. The ARP packet includes the MAC and IP addresses and an operation code for request or reply.

Hackers can use ARP spoofing to corrupt the MAC-to-IP mappings stored in these tables on vulnerable hosts. It is a form of data breach and can cause serious security problems. For example, hackers may block messages to a host or overwhelm it with so many requests that it can’t function.

When ARP was designed in 1982, security was a minor consideration. As a result, the protocol never included any authentication mechanisms, so any device on the network can answer an ARP request. It opens the door for attacks such as ARP poisoning, which involves sending fake ARP responses that trick devices into accepting them.

Type 3

The ARP protocol discovers MAC addresses and maps them to IP addresses. It’s a communication protocol that operates at the data link layer of the OSI model and is used by computers on a local area network (LAN). With it, network devices could send and receive data to each other.

ARP compares a computer’s 32-bit Internet protocol (IP) address to its 48-bit MAC address, which is unique to each computer on a network. It then uses this information to determine a computer’s identity to send and receive data with that machine.

To do so, the source device checks its ARP cache for a record of the target device’s MAC address. If it doesn’t have a record, it broadcasts an ARP request packet to other network devices on the LAN. The other network devices then respond with an ARP response packet containing the target’s MAC address. The source device then uses the received MAC address to connect with the target device.

The ARP protocol is susceptible to spoofing attacks, a cyberattack that can hijack a computer’s session ID. Network administrators can implement security measures to mitigate this issue to ensure ARP is secure. Moreover, they can also configure their ARP protocols to only operate within the local area network.

Type 4

ARP translates layer two information (the hardware address) to layer three (the protocol address). In Ethernet, ARP translates the device’s hardware or MAC address into its network or IP address. This mapping process happens over the link layer and is part of the OSI model of computer networking.

Each LAN technology has its unique way of identifying connected devices. For example, Ethernet identifies devices by their MAC address, which can be assigned to computers, switches, and routers. But when a new computer joins the network, it receives a different address called an Internet Protocol or IP address. IP addresses are logical and based on the network layer, while the MAC address is related to the data link layer.

So when a data packet destined for a specific computer is received by a gateway, it will check to see if the host has a record of that MAC address in its ARP table. If it does, the gateway will transmit the packet to that host. Otherwise, it will broadcast an ARP request to the entire LAN, asking any devices in the area for that computer’s MAC address.

When other network devices receive an ARP request, they will reply with their MAC address to help the first host find the destination machine. It is known as proxy ARP. If the ARP request comes from another network, it is called gratuitous ARP or RARP.