Arp Configuration; Introduction To Arp - 3Com 4200G 12-Port Configuration Manual

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Introduction to ARP

Necessity of the Address
Resolution
ARP Packet Structure
ARP C
ONFIGURATION
Address resolution protocol (ARP) is used to resolve IP addresses into MAC addresses.
IP address is used on the network layer and cannot be used directly for
communication, because network devices can only identify MAC addresses. To enable
packets travel on the network layer to reach the destination host, the MAC address of
the host is required. Therefore, before sending a packet, the sender needs to resolve
the IP address of the destination into the corresponding MAC address.
ARP packets are classified into ARP request packets and ARP reply packets. Table 162
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.
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Table 162 Structure of an ARP request/reply packet
Length of hardware address
Table 163 describes the fields of an ARP packet.
Table 163 Description on the fields of an ARP packet
Field
Hardware Type
Protocol type
Length of the hardware address
Length of protocol address
Operator
Hardware address of the sender
IP address of the sender
Hardware type (16 bits)
Protocol type (16 bits)
Operator (16 bits)
IP Address of the sender
Hardware address of the sender
IP Address of the receiver
Hardware address of the receiver
Description
Identifies the type of the hardware interface.
Refer to Table 164 for the information about
the field values.
Identifies the type of the protocol used by the
sending device. In TCP/IP, it is usually EtherType.
Hardware address length (in bytes)
Protocol address length (in bytes)
Indicates the type of a data packets, which can
be:
1: ARP request packets
2: ARP reply packets
3: RARP request packets
4: RARP reply packets
Hardware address of the sender
IP address of the sender
Length of protocol address