Arp Message Format; Arp Address Resolution Process - H3C S7500E Series Operation Manual

Operation Manual – ARP
H3C S7500E Series Ethernet Switches

1.1.2 ARP Message Format

Figure 1-1 ARP message format
The following explains the fields in
Hardware type: This field specifies the hardware address type. The value "1"
represents Ethernet.
Protocol type: This field specifies the type of the protocol address to be mapped.
The hexadecimal value "0x0800" represents IP.
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".
OP: Operation code. This field specifies the type of ARP message. The value "1"
represents an ARP request and "2" represents an ARP reply.
Sender hardware address: This field specifies the hardware address of the device
sending the message.
Sender protocol address: This field specifies the protocol address of the device
sending the message.
Target hardware address: This field specifies the hardware address of the device
the message is being sent to.
Target protocol address: This field specifies the protocol address of the device the
message is being sent to.

1.1.3 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
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.
Figure 1-1.
Figure 1-2. The resolution process is as follows:
1-2
Chapter 1 ARP Configuration