arp broadcast enable

Function

The arp broadcast enable command enables ARP broadcast on a VLAN tag termination sub-interface.

The undo arp broadcast enable command disables ARP broadcast on a VLAN tag termination sub-interface.

By default, ARP broadcast is disabled on a VLAN tag termination sub-interface.

Format

arp broadcast enable

undo arp broadcast enable

Only 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 this command.

Parameters

None

Views

GE sub-interface view, XGE sub-interface view, 25GE sub-interface view, 40GE sub-interface view, 100GE sub-interface view, Eth-Trunk sub-interface view, MultiGE sub-interface view

Default Level

2: Configuration level

Usage Guidelines

Usage Scenario

VLAN tag termination sub-interfaces discard broadcast packets after receiving the packets. To permit a VLAN tag termination sub-interface to forward broadcast packets, run the arp broadcast enable command on the sub-interface to enable ARP broadcast.

Configuration Impact

When IP packets need to be sent out from the termination sub-interface and there is no corresponding ARP entry on the device, the following situations may occur:

If ARP broadcast is not enabled on the termination sub-interface, the system does not send or forward broadcast ARP packets to learn ARP entries. In this case, the IP packets are discarded directly.
The system tags an ARP broadcast packet and forwards it through the VLAN tag termination sub-interface when ARP broadcast is enabled run on the VLAN tag termination sub-interface.

Precautions

When you enable or disable ARP broadcast on a VLAN tag termination sub-interface, the routing status of the sub-interface becomes Down and then Up. This may result in route flapping on the entire network, affecting services.

After the ARP broadcast function is enabled using the arp broadcast enable command, if a service packet is sent from a termination sub-interface but does not have an ARP entry, an ARP request is copied and sent in all VLANs of the sub-interface. If a large number of VLANs are configured, the number of ARP requests to be copied and sent is large, which may bring a heavy burden on the peer devices that receive the ARP requests. Consequently, the peer devices may encounter exceptions, such as high CPU usage and broadcast suppression. The local device may also fail to immediately send ARP requests as it is busy in processing packet copying, leading to ARP learning failures. To prevent this issue, you are advised to reduce the number of VLANs configured on sub-interfaces.

Example

# Enable ARP broadcast on XGigabitEthernet0/0/1.1.

<HUAWEI> system-view
[HUAWEI] vcmp role silent
[HUAWEI] interface xgigabitethernet 0/0/1
[HUAWEI-XGigabitEthernet0/0/1] port link-type hybrid
[HUAWEI-XGigabitEthernet0/0/1] quit
[HUAWEI] interface xgigabitethernet 0/0/1.1
[HUAWEI-XGigabitEthernet0/0/1.1] dot1q termination vid 10
[HUAWEI-XGigabitEthernet0/0/1.1] arp broadcast enable