1-11 ARP ConfigurationWhen configuring ARP, go to these sections for information you are interested in:z ARP Overviewz Configuring ARPz Configuring Gratuitous ARPz Displaying and Maintaining ARPARP OverviewARP FunctionThe Address Resolution Protocol (ARP) is used to resolve an IP address into an Ethernet MAC address(or physical address).In an Ethernet LAN, when a device sends data to another device, it uses ARP to translate the IPaddress of the destination device to the corresponding MAC address.ARP Message FormatARP messages are classified into ARP requests and ARP replies. Figure 1-1 shows the format of theARP request/reply.Figure 1-1 ARP message formatThe following describe the fields in Figure 1-1.z Hardware type: This field specifies the hardware address type. The value “1” represents Ethernet.z Protocol type: This field specifies the type of the protocol address to be mapped. The hexadecimalvalue “0x0800” represents IP.z Hardware address length and protocol address length: They respectively specify the length of ahardware address and a protocol address, in bytes. For an Ethernet address, the value of thehardware address length field is "6”. For an IP(v4) address, the value of the protocol address lengthfield is “4”.z OP: Operation code. This field specifies the type of the ARP message. The value “1” represents anARP request and “2” represents an ARP reply.z Sender hardware address: This field specifies the hardware address of the device sending themessage.
