3com 5500-SI Manual De Usuario

Introduction to Gratuitous ARP 275

Note that:

■

Static ARP map entry will be always valid as long as the Switch works normally. But 
if the VLAN corresponding to the ARP mapping entry is deleted, the ARP mapping 
entry will be also deleted. The valid period of dynamic ARP map entries will last 
only 20 minutes by default.

■

The parameter 

 must be the ID of a VLAN that has been created by the 

user, and the Ethernet port specified behind this parameter must belong to the 
VLAN.

■

The aggregation port or port with LACP enabled cannot be set as the egress port 
of static ARP.

For purpose of flexible configuration, the system provides the following commands to 
assign dynamic ARP aging period. When the system learns a dynamic ARP entry, its 
aging period is based on the current value configured.

Perform the following configuration in System View.

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

Use the following command to specify whether the Switch should create ARP table 
entries for multicast MAC addresses. Address resolution, for multicast packets, is not 
required because the IANA (Internet Assigned Numbers Authority) have reserved a 
block of Ethernet addresses that map on to the Class D multicast addresses.

Perform the following configuration in System View.

By default, this feature is enabled.

The following are the characteristics of gratuitous ARP packets:

■

Both source and destination IP addresses carried in a gratuitous ARP packet are the 
local IP address, and the source MAC address carried in the packet is the local 
MAC address.

■

If a device finds that the IP address carried in a received gratuitous packet conflict 
with that of its own, it returns an ARP response to the sending device to notify of 
the IP address conflict.

Table 270   Configuring the Dynamic ARP Aging Timer

Configure the dynamic ARP aging timer

 aging_time

Restore the default dynamic ARP aging time

Table 271   Configuring the Creation of ARP Entries for Multicast Packets

Configure the Switch NOT to create ARP entries

Configure the Switch to create ARP entries