3Com 4200G 12-Port Configuration Manual page 311

Figure 1-1 ARP message format
Hardware type (16 bits) Hardware type (16 bits) Hardware type (16 bits)
Protocol type (16 bits) Protocol type (16 bits)
Length of hardware address Length of protocol address Length of hardware address Length of protocol address
Operator (16 bits) Operator (16 bits)
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 Hardware address of the receiver
IP 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
Hardware Type
Protocol type
Length of hardware address
Length of protocol address
Operator
Hardware address of the sender
IP address of the sender
Hardware address of the receiver
IP address of the receiver
Table 1-2 Description on the values of the hardware type field
Value
1
2
3
4
Description
Type of the hardware interface. Refer to
the information about the field values.
Type of protocol address to be mapped. 0x0800
indicates an IP address.
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
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
Ethernet
Experimental Ethernet
X.25
Proteon ProNET (Token Ring)
1-2
Table 1-2
Description
for