Configuring ARP
This chapter describes how to configure the Address Resolution Protocol (ARP).
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.
NOTE:
You can set an Ethernet port as a Layer 3 interface by using the port link-mode route command (see
2—LAN Switching Configuration Guide
ARP message format
ARP uses two types of messages, ARP request and ARP reply.
request/reply. Numbers in the figure refer to field lengths.
Figure 1 ARP message format
•
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. 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
As shown in
follows:
Figure
2, Host A and Host B are on the same subnet. Host A sends a packet to Host B as
).
1
Figure 1
shows the format of the ARP
Layer