Operation Manual – ARPH3C S7500E Series Ethernet Switches Chapter 1 ARP Configuration1-21.1.2 ARP Message FormatFigure 1-1 ARP message formatThe following explains 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 hexadecimal value “0x0800” represents IP.z Hardware address length and protocol address length: They respectively specifythe length of a hardware address and a protocol address, in bytes. For an Ethernetaddress, the value of the hardware address length field is "6”. For an IP(v4)address, the value of the protocol address length field is “4”.z OP: Operation code. This field specifies the type of ARP message. The value “1”represents an ARP request and “2” represents an ARP reply.z Sender hardware address: This field specifies the hardware address of the devicesending the message.z Sender protocol address: This field specifies the protocol address of the devicesending the message.z Target hardware address: This field specifies the hardware address of the devicethe message is being sent to.z Target protocol address: This field specifies the protocol address of the device themessage is being sent to.1.1.3 ARP Address Resolution ProcessSuppose that Host A and Host B are on the same subnet and that Host A sends amessage to Host B, as show in Figure 1-2. The resolution process is as follows:1) Host A looks in its ARP mapping table to see whether there is an ARP entry forHost B. If Host A finds it, Host A uses the MAC address in the entry to encapsulatethe IP packet into a data link layer frame and sends the frame to Host B.
