H3C S7500 Series Ethernet Switches Operation Manual

Operation Manual – ARP
H3C S7500 Series Ethernet Switches Chapter 1
ARP Configuration
1-1
Chapter 1 ARP Configuration
When configuring ARP, go to these sections for information you are interested in:
z Introduction to ARP
z Configuring ARP
z Displaying and Maintaining ARP Configuration
1.1 Introduction to ARP
Address Resolution Protocol (ARP) is used to map network layer protocol addresses
(IP addresses) to corresponding data link layer hardware addresses (MAC addresses).
1.1.1 Necessity of ARP
Network devices can directly identify Layer 2 MAC addresses instead of Layer 3 IP
addresses. For a Layer 3 packet to be received by its destination host, it must carry the
MAC address of the destination host. So, before sending a packet, the source device
must map the destination IP address to the MAC address of the destination device.
1.1.2 ARP Packet Format
There are two types of ARP packets: ARP request and ARP reply. Figure 1-1 illustrates
the structure of the two types of ARP packets. In this figure:
z All fields except for the target hardware address field are used in an ARP request.
The target hardware address is just what the sender wants to obtain.
z All fields are used in an ARP reply.
Hardware type (16 bits)
Protocol type (16 bits)
Length of hardware address Length of pr
Operator (16 bits)
Hardware address of the se
IP address of the sender
Hardware address of the rec
IP address of the receiver
otocol address
nder
eiver
Hardware type (16 bits)Hardware type (16 bits)
Protocol type (16 bits)
Length of hardware address Length of pr
Operator (16 bits)
Hardware address of the se
IP address of the sender
Hardware address of the rec
IP address of the receiver
otocol address
nder
eiver
t Figure 1-1 ARP packet forma