3com 4210 PWR 9-Port 3CR17341-91-ME 用户手册

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:

1 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.

2 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 mode, all hosts on this 
subnet can receive the request, but only the requested host (namely, Host B) will 
process the request.

3 Host B compares its own IP address with the destination IP address in the ARP 

request. If they are the same, Host B saves the source IP address and source MAC 
address into its ARP mapping table, encapsulates its MAC address into an ARP 
reply, and unicasts the reply to Host A.

4 After receiving the ARP reply, Host A adds the MAC address of Host B into its ARP 

mapping table for subsequent packet forwarding. Meanwhile, Host A 
encapsulates the IP packet and sends it out.

Usually ARP dynamically implements and automatically seeks mappings from IP 
addresses to MAC addresses, without manual intervention.

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After the above configuration, you can execute the display command in any view 
to display the running of the ARP configuration, and to verify the effect of the 
configuration.

You can execute the reset command in user view to clear ARP entries.