H3C Technologies H3C SecPath F1000-E - Manual (Page 279)

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Configuring gratuitous ARP
Overview
In a gratuitous ARP packet, both the sender IP address and the target IP address are the IP address of the
device issuing the packet.
A firewall implements the following functions by sending gratuitous ARP packets:
• Determining whether its IP address is already used by another device. After any other device
receives a gratuitous ARP packet, it checks whether the IP address contained in the packet is the
same with its own. If yes, the device returns an ARP reply to notify the sending device of the IP
address conflict.
• Informing other devices about the change of its MAC address so that they can update their ARP
entries.
With the gratuitous ARP packet learning function enabled, a firewall can modify its own ARP entry table
according to the information carried in a received gratuitous ARP packet, including the source IP address
and source MAC address. Upon receiving a gratuitous ARP packet, the firewall looks up its ARP entry
table to check whether there is an ARP entry for the source IP address contained in the packet:
• If not, the firewall creates an ARP entry according to the information carried in the gratuitous ARP
packet.
• If yes, the firewall modifies the corresponding ARP entry according to the information carried in the
gratuitous ARP packet.
With the gratuitous ARP packet learning function disabled, a firewall does not create ARP entries
according to received gratuitous ARP packets; it only modifies existing ARP entries accordingly. If you do
not want ARP entries to be created according to received gratuitous ARP packets, you can disable the
learning function to save ARP entry resources.
Configuring gratuitous ARP in the web interface
Select Firewall > ARP Management > Gratuitous ARP from the navigation tree to enter the page shown
in Figure 162 .
Figure 162 Gratuitous ARP configuration page
Table 43 Configuration items
Item Description
Disable gratuitous ARP packets learning function
Disable learning of ARP entries according to
gratuitous ARP packets.