ARP Protocol-Address Resolution Protocol, 4-Types, Working, Advantages

Today we will tell you about What is ARP Protocol in this blog and how many types are there and will also know the working and message format.

What is ARP Protocol?

The full name of this protocol is ARP (Address Resolution Protocol). This protocol is also known as communication protocol which is used to find the MAC address of the device by the IP address of a device.

This is the 3rd layer of the OSI Model, the most important protocol of the network layer.

The main function of this protocol is to convert 32-bit IP addresses to 48-bit MAC addresses. It is used to determine the MAC address of as many network devices as possible.

When a network device wants to communicate with another network device via a local area network or ethernet. So this protocol is then used.

As you know ARP is a network layer protocol. It is considered a very important protocol in the TCP/IP protocol suite.

It was defined in RFC 826 in the 1982 era. However, it was developed only in the early 80s. Address resolution protocol has been implemented with some important technologies such as IPv4, X.25, frame relay, and ATM.

ARP protocol finds the MAC address based on the IP address of any network device.

The IP address is used to communicate with any network device at the application layer of the OSI model. But if the same is seen, a MAC address is required to communicate or send data packets to any device at the data link layer in the network.

When we send data to a local network host, then this data travels between networks through IP addresses.

But to reach that local area network host in the same LAN, it needs the MAC to address that local host. In this situation, the address resolution protocol plays an important role.

Types of ARP Protocol

It has four types, which are as follows:-

  • Proxy ARP
  • Gratuitous ARP
  • Reverse ARP
  • Inverse ARP
Proxy ARP:-

This is a technique where the network on the proxy server can answer ARP queries from IP addresses that are not on the network.

That is, another network with this proxy server can respond to ARP queries from IP addresses.
In this the sender is stupid. Because the MAC address of the device is used instead of the MAC proxy server address.

Gratuitous ARP:-

Gratuitous ARP is an ARP request made by a computer host, which is used to identify a duplicate IP address.

That is, Gratuitous ARP is used to update the ARP table of other network devices and it also checks whether the computer host is using its original IP address or is using a duplicate IP address.

Reverse ARP:-

Reverse ARP is a network protocol used by a computer host. The computer host uses it to extract information about its own internet protocol (IPv4) from the computer network.

To understand it this way, It is a TCP/IP network protocol by which a computer user can obtain IP address information from a network server.

Inverse ARP 

What is InARP is the inverse of ARP protocol. It is used to find the IP address of the device by MAC address.
It is mainly used in frame relays and ATM networks.

Work of ARP Protocol

The working of address resolution protocol is being explained by some steps:-

ARP Protocol-Address Resolution Protocol
  • When the sender wants to communicate with the receiver, it first checks the ARP cache, it takes information on whether the MAC address of the receiver is already present in the ARP cache or not?
  • If it happens that the MAC address of the receiver is already present in the ARP cache, then the sender will be able to communicate with the receiver using that MAC address.
  • And if the MAC address of a network device does not already have an ARP cache, then in this case an ARP request message is generated by the sender device.

This message contains the sender’s MAC address, the sender’s IP address, and the receiver’s IP address. The field containing the MAC address of the receiver is left blank as it is being searched.

  • The sending device broadcasts this ARP request message over the LAN. Since it is a broadcast message it is connected to the LAN to receive this message for this purpose.
  • All devices derive the IP address of the receiver from this request message to fit the IP address. Those who do not have the address of the device’s IP address for this request message.
  • Match the IP address of the request to the IP address of the recipient that received the message and generate an ARP reply message. It is a unicast message which is sent only to the sender.
  • ARP protocol reply message is used to send a reply message to the sender’s IP address and MAC address. Simultaneously the recipient also sends your IP address and MAC address in this message.
  • It updates the ARP cache with new information (the receiver’s MAC address) as soon as the sending device receives it’s ARP message.
  • Now data can be sent and received in MAC address without hassle to the recipient of the sender.

Advantages of ARP Protocol

Its advantages are given below:-

  • With the help of this protocol, we can easily find the MAC address of any network device.
  • In this protocol, there is no need to configure the end nodes to find the MAC address.

ARP Protocol Message Format

Address resolution protocol is sent to the MAC address to find the MAC address. These messages are broadcast to all the devices on the LAN.

All the field details given in ARP Protocol message format are explained below:-

  • Hardware Type – This is the size of 2 bytes. This field defines the type of hardware used to send the message to the message. The most common type of hardware – is Ethernet. Ethernet has 1 value.
  • This type of protocol – This field tells which protocol has been used to send the message. Most of the 2048 values ​​denote IPv4.
  • Hardware Address Length – This shows the length of the hardware address in bytes. Ethernet MAC addresses have a size of 6 bytes.
  • Protocol Address Length – This refers to the latest IP address. 4 bytes is the size of the IP address.
  • OP Code – This message told the type of the field. If this field has a value of 1, it is a request message and if this field has a value of 2, then it is a reply message.
  • Sender Hardware Address – This MAC address is the device to send the message to.
  • Sender Protocol Address – This is the IP address field of the device to send the message.
  • Target Address Hardware – This field is empty in request messages. This field contains the MAC address of the receiving device.
  • Target Protocol Address – This field contains the IP address of the receiving device.

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