Gratuitous Arp; Configuring Arp Entries; Displaying Arp Entries - HP 1910 User Manual

Dynamic ARP entry
ARP automatically creates and updates dynamic entries. A dynamic ARP entry is removed when its aging
timer expires or the output interface goes down. In addition, a dynamic ARP entry can be overwritten by
a static ARP entry.
Static ARP entry
A static ARP entry is manually configured and maintained. It does not age out and cannot be overwritten
by any dynamic ARP entry.
Using static ARP entries enhances communication security. After a static ARP entry is specified, only a
specific MAC address is associated with the specified IP address. Attack packets cannot modify the
IP-to-MAC mapping. Thus, communications between devices are protected.
NOTE:
Usually ARP dynamically resolves IP addresses to MAC addresses, without manual intervention.

Gratuitous ARP

Gratuitous ARP packets
In a gratuitous ARP packet, the sender IP address and the target IP address are the IP address of the
sending device.
A device sends a gratuitous ARP packet for either of the following purposes:
Determine whether its IP address is already used by another device. If the IP address is already used,
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the device will be informed of the conflict by an ARP reply.
Inform other devices of a MAC address change.
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Gratuitous ARP packets learning
With this feature enabled, a device, upon receiving a gratuitous ARP packet, adds an ARP entry that
contains the sender IP and MAC addresses in the packet to its ARP table. If the corresponding ARP entry
exists, the device updates the ARP entry.
With this feature disabled, the device uses the received gratuitous ARP packets to update existing ARP
entries only.

Configuring ARP entries

Displaying ARP entries

From the navigation tree, select Network > ARP Management. The ARP Table page appears, as shown
in Figure 231.
All ARP entries are displayed on the page.
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