Arp Process - H3C S5500-SI Series Operation Manual

Operation Manual – ARP
H3C S5500-SI Series Ethernet Switches
address, the value of the hardware address length field is "6". For an IP(v4)
address, the value of the protocol address 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 (MAC) address of the
device sending the message.
Sender protocol address: This field specifies the IP 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 IP address of the device the
message is being sent to.

1.1.3 ARP Process

Figure 1-2 ARP proces
Suppose that Host A and Host B are on the same subnet and that Host A sends a
message to Host B. 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.
2) If Host A finds no entry for Host B, Host A buffers the packet and broadcasts an
ARP request, in which the source IP address and source MAC address are
respectively the IP address and MAC address of Host A and the destination IP
address and MAC address are respectively the IP address of Host B and an
all-zero MAC address. As ARP request packet is broadcast, an ARP request
packet is received by all the hosts in the network segment. However, only the
intended host (host B) processes and responds to it.
3) Host B compares its own IP address with the destination IP address in the ARP
request. If they are the same, Host B saves the source IP address and source
Host A
192 .168 . 1 . 1
0002 .6779 .0 f4 c
Source MAC address Source IP address
0002 .6779 .0 f 4 c 192 . 168 . 1 .1
Source MAC address Source IP address
00 a 0 .2470 .febd 192 . 168 . 1 .2
s
1-2
Chapter 1 ARP Configuration
Host B
192 . 168 . 1 .2
00 a0 .2470 .febd
Destination MAC address Destination IP
00 a 0 .2470 .febd 192 .168
Destination MAC address Destination IP
0002 .6779 .0f 4 c
192 . 168
address
. 1 . 2
address
. 1 .1