H3C Technologies H3C SecPath F1000-E - Manual (Page 267)

242
Configuring ARP
The term "router" in this chapter refers to both routers and firewalls.
Overview
ARP resolves IP addresses into physical addresses such as MAC addresses. On an Ethernet LAN, a
device uses ARP to get the MAC address of the target device for a packet.
ARP message format
ARP uses two types of messages, ARP request and ARP reply. Figure 150 shows the format of the ARP
request/reply. Numbers in the figure refer to field lengths.
Figure 150 ARP message format
The following describes the fields in Figure 150 .
• Hardware type—Hardware address type. The value 1 represents Ethernet.
• Protocol type—Type of the protocol address to be mapped. The hexadecimal value 0x0800
represents IP.
• Hardware address length and protocol address length—Length, in bytes, of a hardware address
and a protocol address, in bytes. For an Ethernet address, the value of the hardware address length
field is 6. For an IPv4 address, the value of the protocol address length field is 4.
• OP—Operation code, which describes type of the ARP message. Value 1 represents an ARP request,
and value 2 represents an ARP reply.
• Sender hardware address—Hardware address of the device sending the message.
• Sender protocol address—Protocol address of the device sending the message.
• Target hardware address—Hardware address of the device to which the message is being sent.
• Target protocol address—Protocol address of the device to which the message is being sent.
ARP operation
If Host A and Host B are on the same subnet and Host A sends a packet to Host B, as shown in Figure
151 , the resolution process is: