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Which Destination Address is Used in an ARP Request Frame?

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The Address Resolution Protocol (ARP) is a protocol used by the Internet Protocol (IP), specifically IPv4, to map IP network addresses to the hardware addresses used by a data link protocol. It operates at the Network Layer of the OSI model. The protocol is used when you have a local network IP address and need to find the associated MAC address.

Which Destination Address is Used in an ARP Request Frame?

When an ARP request is sent, it contains the following addresses:

  • Source IP address: The IP address of the device sending the ARP request.
  • Source MAC address: The MAC address of the device sending the ARP request.
  • Target IP address: The IP address of the device for which the ARP request is intended.

Now, coming to the destination address used in an ARP request frame, it is as follows:

  • Destination IP address: This is typically set to the IP address of the device for which the ARP request is intended. However, in the case of an ARP request, this field is not used to route the packet, because ARP requests are always broadcast on the local network.
  • Destination MAC address: In an ARP request, this is set to the broadcast MAC address (FF:FF:FF:FF:FF:FF). This is because the device sending the ARP request does not yet know the MAC address of the target device. By setting the destination MAC address to the broadcast address, the ARP request is sent to all devices on the local network.

Why?

The ARP protocol operates this way to ensure efficient and accurate communication on a network. Here’s why:

  1. Broadcasting the ARP request: Broadcasting the request to all devices on the local network ensures that the device with the matching IP address (if it exists on the network) will receive the request. This is necessary because the device sending the request does not know the MAC address of the target device, so it cannot send the request directly to it.
  2. Using the target IP address: The target IP address is used to identify the device for which the ARP request is intended. Each device on the network will check this address against its IP address. The device with the matching IP address will know it should respond to the ARP request.
  3. Destination MAC address as broadcast address: The destination MAC address is set to the broadcast address because the device sending the request does not know the MAC address of the target device. Using the broadcast address, the request is sent to all devices on the network, ensuring that the target device will receive it.

This process allows a device to discover the MAC address of another device on the same network given only its IP address.

This is crucial for enabling communication on the network, as MAC addresses are used for directing data packets to devices on a local network.

Without ARP, there would be no straightforward way for a device to send data to another device on the network unless it already knew its MAC address.

In summary, an ARP request is broadcasted to all devices on the local network using the broadcast MAC address in the destination MAC address field.

The target IP address is set to the IP address of the device for which the MAC address is required. The device with the matching IP address will respond with its MAC address.

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