multicast drop-unknown

Function

The multicast drop-unknown command configures the switch to drop unknown multicast flows in a VLAN.

The undo multicast drop-unknown command restores the default measure taken for unknown multicast flows.

The default method that a switch uses to process unknown multicast flows depends on whether Layer 2 multicast is enabled and which Layer 2 multicast forwarding mode is used.

Format

multicast drop-unknown

undo multicast drop-unknown

Parameters

None

Views

VLAN view

Default Level

2: Configuration level

Usage Guidelines

Usage Scenario

Unknown multicast flows are those that do not match any entry in the multicast forwarding table or match multicast forwarding entries with an empty outbound interface list. These flows are not requested by users. The default method that a switch uses to process unknown IPv4 multicast flows depends on whether Layer 2 multicast is enabled and which Layer 2 multicast forwarding mode is used:

If Layer 2 multicast is not enabled on the switch, the switch broadcasts unknown multicast flows in the corresponding VLAN.
If Layer 2 multicast is enabled on the S2720-EI, they broadcast unknown multicast flows in the corresponding VLAN.
If Layer 2 multicast is enabled on other switch models, they broadcast unknown multicast flows in the corresponding VLAN in MAC address-based forwarding mode and drop unknown multicast flows in IP address-based forwarding mode.

If a switch broadcasts unknown multicast flows in a VLAN, you can configure the switch to drop unknown multicast flows, reducing instant bandwidth usage.

Configuration Impact

After the multicast drop-unknown command is executed, all unknown IPv4 and IPv6 multicast packets are dropped, including the protocol packets that are transparently transmitted within the VLAN and use the reserved multicast address.

For the S5735-L, S5735S-L, S5735S-L-M, S5735-S, S5735-S-I, and S5735S-S, if MAC address-based forwarding is configured as the Layer 2 multicast forwarding mode and the multicast drop-unknown command is executed, unknown multicast packets destined for the following reserved network segments and IP address cannot be dropped: 239.0.0.0/8, 224.0.0.0/24, 224.0.1.0/24, FF0X:0:0:0:0:0:0:0/96, FF0X::DB8:0:0/96, and the IPv6 address with the last 32 bits being 0000:00XX. To drop such unknown multicast packets, configure a traffic policy.

Example

# Drop unknown multicast packets in VLAN 10.

<HUAWEI> system-view
[HUAWEI] vlan 10
[HUAWEI-vlan10] multicast drop-unknown