Gratuitous arp, Introduction to gratuitous arp – H3C Technologies H3C SecPath F1000-E User Manual
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# Create a static ARP entry.
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Select Firewall > ARP Management > ARP Table from the navigation tree and click Add to
perform configurations shown in
.
Figure 9 Create an ARP entry
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Type 192.168.1.1 for IP Address.
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Type 00e0-fc01-0000 for MAC Address.
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Select the Advanced Options checkbox.
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Type 10 for VLAN ID.
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Select GigabitEthernet0/1 for Port.
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Click Apply.
Gratuitous ARP
Introduction to Gratuitous ARP
In a gratuitous ARP packet, the sender IP address and the target IP address are both the IP address of
the device issuing the packet, the sender MAC address is the MAC address of the device, and the target
MAC address is the broadcast address ff:ff:ff:ff:ff:ff.
A device 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 device 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 device looks up its ARP
entry table to check whether there is an ARP entry for the source IP address contained in the packet:
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If not, the device creates an ARP entry according to the information carried in the gratuitous ARP
packet.