3com 8807 User Guide
Displaying and Debugging ARP
675
■
If a device finds that the IP addresses carried in a received gratuitous packet
conflict with those of its own, it returns an ARP response to the sending device
to notify of the IP address conflict.
conflict with those of its own, it returns an ARP response to the sending device
to notify of the IP address conflict.
By sending gratuitous ARP packets, a network device can:
■
Determine whether or not IP address conflicts exist between it and other
network devices.
network devices.
■
Trigger other network devices to update its hardware address stored in their
caches.
caches.
With the gratuitous ARP packet learning function enabled, a network device
stores the ARP address carried in a received gratuitous ARP packet in its ARP
address table if no ARP address in the cache of the network device matches the IP
address carried by the gratuitous ARP packet. If the cache contains an ARP entry
that matches the received gratuitous ARP packet, the switch updates the ARP
entry using the hardware address of the sender carried in the gratuitous ARP
packet. A switch operates like this whenever it receives an ARP packet.
stores the ARP address carried in a received gratuitous ARP packet in its ARP
address table if no ARP address in the cache of the network device matches the IP
address carried by the gratuitous ARP packet. If the cache contains an ARP entry
that matches the received gratuitous ARP packet, the switch updates the ARP
entry using the hardware address of the sender carried in the gratuitous ARP
packet. A switch operates like this whenever it receives an ARP packet.
Gratuitous ARP packet learning configuration
The following table lists the operations to configure the gratuitous ARP packet
learning function.
learning function.
Configuring ARP Packets
Not to Broadcast in
VLAN
In order to disable the mutual access function for two devices in the same network
segment, you can manually control ARP packets and send them as trap packets to
the CPU, so that ARP request packets will not be broadcast in the VLAN. Thus, the
two devices cannot learn the addresses of each other from ARP packets and the
function above is implemented.
segment, you can manually control ARP packets and send them as trap packets to
the CPU, so that ARP request packets will not be broadcast in the VLAN. Thus, the
two devices cannot learn the addresses of each other from ARP packets and the
function above is implemented.
Displaying and
Debugging ARP
Debugging ARP
After the above configuration, execute the display command in any view to
display the running of the ARP configuration, and to verify the effect of the
configuration.
display the running of the ARP configuration, and to verify the effect of the
configuration.
Table 612 Configure the gratuitous ARP packet learning function
Operation
Command
Description
Enter system view
system-view
-
Enable the gratuitous ARP
packet learning function
packet learning function
gratuitous-arp-learning
enable
enable
Required
By default, the gratuitous ARP
packet learning function is
enabled.
packet learning function is
enabled.
Table 613 Configure non-flooding ARP request packets in VLAN
Operation
Command
Description
Enter system view
system-view
-
Enter Ethernet port view
interface interface-type
interface-number
interface-number
The port specified by the
interface-type argument can
be Ethernet port only
interface-type argument can
be Ethernet port only
Enable ARP non-flooding in a
VLAN
VLAN
arp non-flooding enable
Required
This function is disabled by
default
default