H3C Technologies H3C WX6000 Series Access Controllers - Manual (Page 364)

33-2
ARP Message Format
Figure 33-1 ARP message format
The following explains the fields in Figure 33-1 .
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 specify the length 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 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 device sending the
message.
z
Sender protocol address: This field specifies the protocol address of the device sending the
message.
z
Target hardware address: This field specifies the hardware address of the device the message is
being sent to.
z
Target protocol address: This field specifies the protocol address of the device the message is
being sent to.
ARP Address Resolution Process
Suppose that Host A and Host B are on the same subnet and that Host A sends a message to Host B,
as show in
Figure 33-2 . The resolution process is as follows:
1) Host A looks in its ARP mapping table to see whether there is an ARP entry for Host B. If Host A
finds it, Host A uses the MAC address in the entry to encapsulate the IP packet into a data link layer
frame and sends the frame to Host B.