3Com 10014298 Dhcp Relay, Configuring the Dynamic ARP Aging Timer, Displaying and Debugging ARP

72 CHAPTER 4: NETWORK PROTOCOL OPERATION

Table 66 Learning Gratuitous ARPs

Operation	Command
Prevent the switch from learning gratuitous	undo gratuitous-arp-learning
ARPs	enable

By default, the switch does not learn gratuitous ARPs.

Configuring the Dynamic ARP Aging Timer

The following commands assign a dynamic ARP aging period to enable flexible configurations. When the system learns a dynamic ARP entry, its aging period is based on the currently configured value.

Perform the following configuration in system view.

Table 67 Configure the Dynamic ARP Aging Timer

Operation	Command
Configure the dynamic ARP aging timer	arp timer aging aging-time
Restore the default dynamic ARP aging time	undo arp	timer aging

By default, the aging time of the dynamic ARP aging timer is 20 minutes.

Displaying and Debugging ARP

After the previous configuration, execute display command in all views to display the operation of the ARP configuration, and to verify the effect of the configuration. Execute the debugging command in user view to debug the ARP configuration.

Table 68 Display and Debug ARP

Operation	Command
Display ARP mapping table	display arp [ ip-address [
	static dynamic ] [ { begin
	include exclude } text ] ]
Display the current setting of the dynamic ARP	display arp timer aging
map aging timer
Enable ARP information debugging	debugging arp { packet status }
Disable ARP information debugging	undo debugging arp { packet
	status }

By default, all ARP mapping entries of the Ethernet switch are displayed.

DHCP Relay	Dynamic Host Configuration Protocol (DHCP) offers dynamic IP address
	assignment. DHCP works in Client-Server mode. With this protocol, the DHCP
	Client can dynamically request configuration information and the DHCP server can
	configure the information for the Client.
	The DHCP relay serves as conduit between the DHCP Client and the server located
	on different subnets. The DHCP packets can be relayed to the destination DHCP
	server (or Client) across network segments. The DHCP clients on different
	networks can use the same DHCP server. This is economical and convenient for
	centralized management.