What is the role of ARP in addressing?

The ARP protocol is responsible for mapping IP addresses to MAC addresses. MAC address is a physical address that works in the data link layer in the TCP/IPTransfer Control Protocol Internet Protocol model.

Note: To read more about MAC addresses, refer here.

Role of ARP in addressing

One of the significant protocols of the network layer in the OSI model is the Address Resolution Protocol (ARP), which assists in determining the MAC address provided by the IP address of the device present on the network. The primary function of the ARP is to convert the 32-bit IP addressIPv4 to the 48-bit MAC address.

ARP

Address Resolution Protocol (ARP) is a request-response or request-reply protocol in which one device requests information, and the other replies by providing the requested information. ARP packets are distributed solely within a specific network and are encapsulated by the link layer. Therefore, ARP is referred to as a link layer protocol.

Note: ARP request is generally referred as broadcastRequest sent to all the nodes present on the network, and ARP response is unicastResponse sent to the only corresponding device which requested it.

Need

MAC addresses rather than IP addresses are used for communication by the underlying ethernet devices or LAN. For this purpose, ARP protocol comes into the picture.

Working

The following steps will help to understand the role of ARP protocol in addressing:

• When a source wants to determine the MAC address of a destination device at the network layer, it first checks the ARP cache or ARP tableThe ARP sends the resolved MAC address to the source, which is stored in a table for further use. . If present, it will communicate using that MAC address.

• The source device will produce an ARP requestIt broadcasts a packet over the network, to check if the destination MAC address is found or not. message if the MAC address is not already present in the ARP table. The source includes its own MAC address, IP address, and destination IP address in the request message, leaving the destination MAC address empty because the source is seeking to locate it.

ARP request is illustrated as:

• The source device will broadcast the ARP request message to the local network.

• Every other device in the LAN network receives the broadcast message.

• Each device will now check the destination's IP address against its IP address. ARP replyThe response that the source receives from the destination helps with subsequent data transmission. message is sent if the destination's IP address matches. The device will only drop the packet if the IP address does not match.

• The device whose IP address matches the destination IP address in the packet sends an ARP reply message. The destination device modifies its ARP table and saves the source's MAC address because it will need to get in touch with the source shortly. For this device, the source is now the destination, and the ARP reply message is sent.

ARP reply is visualized as:

• The source updates its ARP cache and learns the destination MAC address when it receives the ARP reply. Now that the source knows the destination MAC address, the packets are exchanged smoothly.