3Com Switch 7750 Configuration Guide Guide

52
ARP CONFIGURATION
Introduction to ARP Address resolution protocol (ARP) is used to map IP addresses to the
corresponding MAC addresses so that packets can be delivered to their
destinations correctly.
Necessity of the Address
Resolution
After a packet is forwarded to the destination network, MAC address is necessary
for the packet to reach the very device. So the destination IP address carried in a
packet need to be translated into the corresponding MAC address.
ARP Packet Structure ARP packets are classified as ARP request packets and ARP reply packets.
Figure 141 illustrates the structure of these two types of ARP packets.
■ As for an ARP request packet, all the fields except the hardware address of the
receiver field are set. The hardware address of the receiver is what the sender
request for.
■ As for an ARP reply packets, all the fields are set.
Figure 141 Structure of an ARP request/reply packet
Table 415 describes the fields of an ARP packet.
IP address of the receiver
Hardware address of the receiver
IP address of the sender
Hardware address of the sender
Operator (16 bits)
Length of the hardware address Length of protocol address
Protocol type (16 bits)
Hardware type (16 bits)