What is Address Resolution Protocol : Working & Its Applications

Generally, the IP address or logical address is used by most computer programs or computer applications to transmit or receive messages. But actually, the communication takes place over the MAC address or physical address that is from layer-2 of the OSI model (TCP/IP). So to get the destination MAC address to communicate with other devices, the address resolution protocol is used. The functionality of ARP is to convert the IP address into physical addresses.

In the OSI model, the ARP is one of the most essential protocols of the Network. This protocol finds the address of hardware which is called as MAC (Media Access Control) address. This article discusses an overview of address resolution protocol basics or ARP.

What is Address Resolution Protocol?

Address resolution protocol definition is, a protocol which is used to connect an ever-changing IP address to an address of fixed physical machine like MAC (media access control) address within a LAN is known as address resolution protocol.

This mapping process is significant because the IP & MAC addresses the change & conversion of the length so that the systems can identify one another. At present, the most frequently used IP is IPv4 (IP version 4). An IP address is 32-bits long whereas a MAC address is 48-bits long. Address resolution protocol changes the 32 address bit into 48 address bit. The address resolution protocol diagram is shown below.

In the OSI networking model, there are different layers that provide an idea of what is going on with a specific networking system to IT teams. So that they can determine which network layer is affecting the device, application, or the installed software on the network. So that the IT engineer is responsible for handling the specific layer.

The MAC address or media access control address is also called the data link layer. This layer setups & finishes a connection in between two physically coupled devices so that transfer of data can occur. The internet protocol address can be defined as the network layer which is accountable for forwarding data packets using different routers. Here, address resolution protocol works in between layers like IP & MAC

How does Address Resolution Protocol Work?

The example of address resolution protocol is discussed below. When the source at the network layer wants to converse with the destination, first the source requires discovering the Physical Address or MAC address of the destination. For this, the source will verify the ARP table or ARP cache with the destination of the MAC address. If this destination address is available within the ARP table or ARP cache, then the source utilizes the address of MAC for communication.

If the address of MAC for the destination is not available in the ARP table or cache, then the source will generate a request message of an ARP. The ARP table is mainly used to maintain a connection between every MAC address & its equivalent IP address. This table can be entered manually by the user. Here, the request message includes the IP address & MAC address of the source and the destination. The destination’s MAC address will leave null since the user has demanded this.

The request message of an address resolution protocol will be transmitted to the local network through the source computer. In the network of LAN, all the devices will get the broadcast message. Now, every device evaluates its own IP address through the destination IP address.

If both the IP address of the device and the destination match, then the device will send an ARP to reply message. Similarly, if the IP address does not match, then the device will drop the packet automatically.

The destination transmits an address resolution protocol reply packet once the address of the destination equals the device. The reply packet of ARP includes the device’s MAC address. The destination device updates the table automatically to store the MAC address of the source as this address will be necessary from the source for communication purposes.

At present, the source for the destination device performs like a target & the destination device transmits the reply message of ARP which is unicast rather than broadcast.

Once the source device gets the reply message of ARP, then it will recognize the destination devices’ MAC address because the reply packet of ARP includes the destination device’s MAC address with the other addresses. Here, the MAC address will be updated by the destination MAC address within the ARP cache. So the sender is capable to converse to the destination directly.

Address Resolution Protocol Types

There are four types of ARP which include the following.

• Proxy ARP
• Gratuitous ARP
• Reverse ARP (RARP)
• Inverse ARP

Proxy ARP

Proxy ARP is a system that replies to the requests of ARP on the behalf of a different system. Once the request is sent through an outside system of the network host, the router functions as a gateway to transmit the packets outside of the networks to their destinations.

Reverse ARP (RARP)

Reverse ARP is a convention used through the framework of the customer within LAN to command its IPv4 address from the gateway-router table. A table is prepared by the manager of the organization within the gateway router that is used to determine the address of MAC to the connecting IP address.

Gratuitous ARP

The gratuitous ARP is a type of protocol that requests from the broadcast to obtain the IP address of the router. It is mainly utilized once an end system includes an IP address however wishes to protect its MAC address from the local area network if the address of IP is not used through any other system.

This protocol is mainly used to update the table of ARP for other devices. It also verifies whether the host is utilizing the actual IP address otherwise a duplicate one.

Inverse ARP

The inverse of ARP is known as Inverse ARP which is mainly utilized to find out the system’s IP addresses over local area network from its MAC addresses. It is most frequently used in frame relays, ATM networks where the data from level-3 to level 2 are obtained.

Address Resolution Protocol Vs Reverse Address Resolution Protocol

Both the ARP & RARP are LAN protocols which are quite the same in some ways. Both the protocols have the objective to complete the mapping from IP to MAC address. The difference between Arp and RARP includes the following.

Advantages

The advantages of address resolution protocol include the following.

• By using an ARP, the address of MAC can be known simply if you know the same system’s IP address.
• End nodes should not be arranged to identify MAC addresses. It can be found once required.
• The main goal of this protocol is to allow every host on a network that permits you to increase a mapping in between two addresses like IP & physical.
• The set of mappings stored within the host is known as ARP cache/table.

Disadvantages

The disadvantages of address resolution protocol include the following.

• ARP attacks may occur like ARP spoofing & Denial of Services.
• ARP Spoofing is a method used to allow an attacker for attacking an Ethernet Network. This network may lead to data frames sniffing on switched LAN otherwise the attacker may end the overall traffic which is also called ARP denial of Services.

Applications

The applications of address resolution protocol include the following.

• The address resolution protocol or ARP is the first network-level protocol that translates addresses of the Internet into an exclusive hardware address on LANs.
• A communication protocol like ARP is mainly used for noticing the address of the link-layer like a MAC address which is associated through an address of a given internet layer, normally an IPv4 address.
• This type of protocol is mainly used to discover the address of MAC for a device from its IP address.
• It is used when a device needs to converse with another device on a LAN or Ethernet.
• This protocol is required because the IP address of the computer linked to the network needs to be changed to a MAC address.

Thus, this is all about an overview of an address resolution protocol. This is one of the main protocols within the OSI layer model. The main function of ARP is to map a 32- bit logical address into a 48-bit MAC address. Here is a question for you, in which layer of the OSI model, the ARP is available?