3Com WX3000 operation manual ARP Table, ARP Process, Chaos, ARC network

Value	Description
5	Chaos
6	IEEE802.X
7	ARC network

ARP Table

In an Ethernet, the MAC addresses of two hosts must be available for the two hosts to communicate with each other. Each host in an Ethernet maintains an ARP table, where the latest used IP address-to-MAC address mapping entries are stored. The device provides the display arp command to display the information about ARP mapping entries.

ARP entries in a device can either be static entries or dynamic entries, as described in Table 1-3.

Table 1-3ARP entries

ARP entry	Generation Method	Maintenance Mode
Static ARP entry	Manually configured	Manual maintenance
Dynamic ARP entry	Dynamically generated	ARP entries of this type age with time. The aging
		period is set by the ARP aging timer.

ARP Process

Figure 1-2 ARP process

Host A 192. 168.1.1 0002-6779-0f4c

Sender MAC	Sender IP	Target MAC
address	address	address
0002 -6779 -0f4c	192 .168.1.1	0000 -0000-0000

Host B 192. 168.1.2 00a0-2470 -febd

Target IP address 192.168 .1. 2

Sender MAC	Sender IP		Target MAC	Target IP
address	address		address	address
00a0-2470 -febd	192.168.1.	2	0002-6779-0f4c	192.168.1.1

Suppose that Host A and Host B are on the same subnet and that Host A sends a message to Host B. The resolution process is as follows:

2)Host A looks in its ARP mapping table to see whether there is an ARP entry for Host B. If Host A finds it, 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.

3)If Host A finds no entry for Host B, Host A buffers the packet and broadcasts an ARP request, in which the source IP address and source MAC address are respectively the IP address and MAC address of Host A and the destination IP address and MAC address are respectively the IP address of Host B and an all-zero MAC address. Because the ARP request is sent in broadcast

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