igmp-snooping fast-switch enable

Usage Scenario

When the Layer 2 network topology changes, multicast forwarding paths may change. You can configure the switch to send Query messages upon topology changes using the igmp-snooping send-query enable command. In this way, multicast data flows can be switched to new forwarding paths quickly after the Layer 2 network topology changes. However, the downstream device may not receive the Query message immediately after convergence of the Layer 2 network, because the Query message is sent after a certain interval (60s by default). As a result, multicast traffic cannot be quickly switched to the new forwarding paths.

If the Layer 2 network is running the Spanning Tree Protocol (STP), you can enable fast multicast forwarding path switching upon STP topology changes. When the STP topology changes, this function quickly changes the ports in Forwarding state into router ports to direct multicast data flows to the new forwarding paths.

Prerequisite

Global IGMP snooping has been enabled using the igmp-snooping enable (system view) command.

Precautions

• This function takes effect only when STP is used as the loop prevention protocol on a Layer 2 network and the STP operation mode is MSTP, RSTP, or STP.
• With this function configured, the switch sets all ports in Forwarding state as router ports when the STP topology changes. In this case, multicast data flows are forwarded to all the router ports before the router ports are aged. This will cause increase in multicast traffic on the network.