3Com 10014298 manual Manually Adding/Deleting Static ARP Mapping Entries, Learning Gratuitous ARPs

Configuring Address Resolution Protocol (ARP) 71

corresponding MAC address is not found, Host A will store the IP packet in the queue waiting for transmission, and broadcast an ARP request to attempt to resolve the MAX address of Host B.

The ARP request packet contains the IP address of Host B and the IP address and MAC address of Host A. Since the ARP request packet is broadcast, all hosts on the network segment receive the request. However, only the requested host (i.e., Host B) needs to process the request. Host B will first store the IP address and the MAC address of the request sender (Host A) from the ARP request packet in its own ARP mapping table. Host B will then generate an ARP reply packet and add the MAC address of Host B before sending it to Host A. The reply packet will be sent directly to Host A instead of being broadcast. Upon receiving the reply packet, Host A will extract the IP address and the corresponding MAC address of Host B and add them to its own ARP mapping table. Then Host A will send Host B all the packets standing in the queue.

Normally, dynamic ARP executes and automatically attempts to resolve the IP address to an Ethernet MAC address with no intervention from the administrator.

Configuring ARP The ARP mapping table can be maintained dynamically or manually. Addresses that are mapped manually are referred to as static ARP. The user can display, add, or delete the entries in the ARP mapping table through manual commands.

ARP configuration includes tasks described in the following sections:

■Manually Adding/Deleting Static ARP Mapping Entries

■Learning Gratuitous ARPs

■Configuring the Dynamic ARP Aging Timer

■Displaying and Debugging ARP

Manually Adding/Deleting Static ARP Mapping Entries

Perform the following configuration in System view.

Table 65 Manually Adding/Deleting Static ARP Mapping Entries

Operation	Command
Manually add a static ARP mapping entry	arp static ip-address mac-address
	VLANID { interface_type
	interface_num interface_name }
Manually delete a static ARP mapping entry	undo arp static ip-address

Static ARP mapping entries will not time out, however dynamic ARP mapping entries time out after 20 minutes.

The ARP mapping table is empty and the address mapping is obtained through dynamic ARP by default.

Learning Gratuitous ARPs

Perform the following configuration in System view.

Table 66 Learning Gratuitous ARPs

Operation	Command
Enable the switch to learn gratuitous ARPs	gratuitous-arp-learning enable