Arp Management; Arp Overview; Arp Function; Arp Message Format - 3Com Baseline 2928 PWR Plus User Manual

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ARP Management

ARP Overview

ARP Function

The Address Resolution Protocol (ARP) is used to resolve an IP address into an Ethernet MAC address
(or physical address).
In an Ethernet LAN, when a device sends data to another device, it uses ARP to translate the IP
address of the destination device to the corresponding MAC address.

ARP Message Format

ARP messages are classified into ARP requests and ARP replies.
ARP request/reply.
Figure 1-1 ARP message format
The following describe 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 the 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.
Figure 1-1.
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Figure 1-1 shows the format of the