arp learning strict (interface view)

Function

The arp learning strict command enables strict ARP learning on the interface.

The undo arp learning strict command restores the global configuration on the interface.

By default, strict ARP learning is disabled on the interface.

Format

arp learning strict { force-enable | force-disable | trust }

undo arp learning strict

Parameters

Parameter	Description	Value
force-enable	Indicates that strict ARP learning is enabled.	-
force-disable	Indicates that strict ARP learning is disabled.	-
trust	Indicates that the configuration of strict ARP learning is the same as the global configuration. NOTE: The effect of the trust parameter is the same as the effect of the undo arp learning strict command.	-

Views

Interface view

Default Level

2: Configuration level

Usage Guidelines

Usage Scenario

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.

Prerequisites

On an Ethernet interface working in Layer 2 mode, the undo portswitch command has been run to switch the interface to Layer 3 mode.

Only the S5720-EI, S5720-HI, S5730-HI, S5731-H, S5731-S, S5731S-H, S5731S-S, S5732-H, S6720-EI, S6720-HI, S6720S-EI, S6730-H, S6730S-H, S6730-S, and S6730S-S support switching between Layer 2 and Layer 3 modes.

Precautions

The configuration on an interface takes precedence over the global configuration.

When ARP attacks occur on many interfaces of the device, you can run the arp learning strict command to enable strict ARP learning globally.

Example

# Enable strict ARP learning on VLANIF 100.

<HUAWEI> system-view
[HUAWEI] vlan 100
[HUAWEI-vlan100] quit
[HUAWEI] interface vlanif 100
[HUAWEI-Vlanif100] arp learning strict force-enable

# Enable strict ARP learning on Layer 3 interface GE0/0/1.

<HUAWEI> system-view
[HUAWEI] interface gigabitethernet 0/0/1
[HUAWEI-GigabitEthernet0/0/1] undo portswitch
[HUAWEI-GigabitEthernet0/0/1] arp learning strict force-enable