2-1This document is organized as follows:z ARP Configurationz Proxy ARP Configurationz ARP Attack Defense Configuration2 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 MACaddress (or physical address).In a LAN, when a host or other network device is to send data to another host or device, the sendinghost or device must know the network layer address (that is, the IP address) of the destination host ordevice. Because IP datagrams must be encapsulated within Ethernet frames before they can betransmitted over physical networks, the sending host or device also needs to know the physicaladdress of the destination host or device. Therefore, a mapping between the IP address and thephysical address is needed. ARP is the protocol to implement the mapping function.ARP Message FormatFigure 2-1 ARP message formatThe following explains the fields in Figure 2-1.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 the
