Strict ARP Learning

Context

If many user hosts send a large number of ARP packets to a device simultaneously, or attackers send bogus ARP packets to the device, the following problems occur:

Processing ARP packets consumes many CPU resources. The device learns many invalid ARP entries, which exhaust ARP entry resources and prevent the device from learning ARP entries for ARP packets from authorized users. Consequently, communication of authorized users is interrupted.
After receiving bogus ARP packets, the device incorrectly modifies the ARP entries. As a result, authorized users cannot communicate with each other.

To avoid the preceding problems, enable strict ARP learning on the gateway. This function indicates that the device learns only ARP entries for ARP Reply packets in response to ARP Request packets sent by itself, but does not allow the device to learn the ARP entries for the ARP packets received from other devices. In this way, the device can defend against most ARP attacks.

Procedure

Configuring global strict ARP learning
1. Choose Configuration > Security Services > IP Security > Strict ARP Learning. The Strict ARP Learning page is displayed.
2. Click the button next to Strict ARP Learning to enable the global strict ARP learning function.
Configuring strict ARP learning on an interface
1. Choose Configuration > Security Services > IP Security > Strict ARP Learning. The Strict ARP Learning page is displayed.
2. Select the name of a target interface, or click in the entry of a target interface.
  - Click Enable or select Enable from the drop-down list to enable strict ARP learning on the interface.
  - Click Disable or select Disable from the drop-down list to disable strict ARP learning on the interface.
  - Click As Per Global or select As Per Global from the drop-down list to configure strict ARP learning on the interface to be the same as the global strict ARP learning function.
3. Click Refresh to update the interface configuration list, and check strict ARP learning on the interface.