Ignoring Spanning-Tree Topology Change Messages

By default the IGMP snooping process on an MX Series router detects interface state changes made by any of the spanning tree protocols (STPs).

In a VPLS multihoming environment where two PE routers are connected to two interconnected CE routers and STP root protection is enabled on the PE routers, one of the PE router interfaces is in forwarding state and the other is in blocking state.

If the link interconnecting the two CE routers fails, the PE router interface in blocking state transitions to the forwarding state.

The PE router interface does not wait to receive membership reports in response to the next general or group-specific query. Instead, the IGMP snooping process sends a general query message toward the CE router. The hosts connected to the CE router reply with reports for all groups they are interested in.

When the link interconnecting the two CE routers is restored, the original spanning-tree state on both PE routers is restored. The forwarding PE receives a spanning-tree topology change message and sends a general query message toward the CE router to immediately reconstruct the group membership state.

The default behavior for the IGMP snooping process on an MX Series router can be changed to ignore messages about the spanning-tree topology state change.

To ignore the spanning-tree interface state, include the ignore-stp-topology-change statement:

You can include this statement at the following hierarchy levels:

• [edit bridge-domains bridge-domain-name multicast-snooping-options]
• [edit routing-instances routing-instance-name bridge-domains bridge-domain-name multicast-snooping-options]

Note: The ignore-stp-topology-change statement is supported for the virtual-switch routing instance type only.