3Com 4200G 24-Port - Page 311

1-2
Figure 1-1 ARP message format
Hardware type (16 bits)
Protocol type (16 bits)
Length of hardware address
Length of protocol address
Operator (16 bits)
Hardware address of the sender
IP address of the sender
Hardware address of the receiver
IP address of the receiver
Hardware type (16 bits)Hardware type (16 bits)
Protocol type (16 bits)
Length of hardware address
Length of protocol address
Operator (16 bits)
Hardware address of the sender
IP address of the sender
Hardware address of the receiver
IP address of the receiver
Table 1-1 describes the fields of an ARP packet.
Table 1-1 Description on the fields of an ARP packet
Field Description
Hardware Type
Type of the hardware interface. Refer to
Table 1-2 for
the information about the field values.
Protocol type
Type of protocol address to be mapped. 0x0800
indicates an IP address.
Length of hardware address Hardware address length (in bytes)
Length of protocol address Protocol address length (in bytes)
Operator
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 Hardware address of the sender
IP address of the sender IP address of the sender
Hardware address of the receiver
For an ARP request packet, this field is null.
For an ARP reply packet, this field carries the hardware
address of the receiver.
IP address of the receiver IP address of the receiver
Table 1-2 Description on the values of the hardware type field
Value Description
1 Ethernet
2 Experimental Ethernet
3 X.25
4 Proteon ProNET (Token Ring)