Chapter 1 Arp Configuration; Introduction To Arp - H3C S9500 Series Operation Manual

Operation Manual – ARP
H3C S9500 Series Routing Switches

Chapter 1 ARP Configuration

When configuring ARP, go to these sections for information you are interested in:

Introduction to ARP

Configuring ARP
Displaying and Debugging ARP
1.1 Introduction to ARP
Address resolution protocol (ARP) is used to resolve an IP address into a MAC
address.
I. Why ARP
An IP address cannot be directly used for communication on an Ethernet because
network devices can identify only MAC addresses. An IP address is a network layer
address. To send datagrams through the network layer to the destination host, the MAC
address of the host is required. Therefore, the IP address must be resolved into a MAC
address.
II. ARP address resolution process
Figure 1-1 ARP address resolution process
Suppose that Host A and Host B are on the same subnet and Host A sends a packet to
Host B. The resolution process is as follows:
1) Host A checks its ARP table to see whether there is an ARP entry for Host B. If yes,
Host A uses the MAC address in the entry to encapsulate the IP packet into a data
link layer frame and sends the frame to Host B.
2) If Host A finds no entry for Host B, Host A buffers the packet and broadcasts an
ARP request, in which the sender IP address and sender MAC address are
respectively the IP address and MAC address of Host A and the target IP address
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Chapter 1 ARP Configuration