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Example: Configuring MLD Snooping on Switches with ELS Support


This example uses Junos OS with support for the Enhanced Layer 2 Software (ELS) configuration style. For ELS details, see Using the Enhanced Layer 2 Software CLI.

You can enable MLD snooping on a VLAN to constrain the flooding of IPv6 multicast traffic on a VLAN. When MLD snooping is enabled, a switch examines MLD messages between hosts and multicast routers and learns which hosts are interested in receiving multicast traffic for a multicast group. On the basis of what it learns, the switch then forwards IPv6 multicast traffic only to those interfaces connected to interested receivers instead of flooding the traffic to all interfaces.

This example describes how to configure MLD snooping:


This example uses the following software and hardware components:

  • One switch running Junos OS with ELS

  • Junos OS Release 13.3 or later for EX Series switches or Junos OS Release 15.1X53-D10 or later for QFX10000 switches

Before you configure MLD snooping, be sure you have:

  • Configured the vlan 100 VLAN on the switch.

  • Assigned interfaces ge-0/0/0, ge-0/0/1, ge-0/0/2, and ge-0/0/12 to vlan100.

  • Configured ge-0/0/12 as a trunk interface.

See Configuring VLANs for EX Series Switches or Configuring VLANs on Switches with Enhanced Layer 2 Support.

Overview and Topology

In this example, interfaces ge-0/0/0, ge-0/0/1, and ge-0/0/2 on the switch are in vlan100 and are connected to hosts that are potential multicast receivers. Interface ge-0/0/12, a trunk interface also in vlan100, is connected to a multicast router. The router acts as the MLD querier and forwards multicast traffic for group ff1e::2010 to the switch from a multicast source.


The topology for this example is illustrated in Figure 1.

Figure 1: MLD Snooping Topology ExampleMLD Snooping Topology Example

In this sample topology, the multicast router forwards multicast traffic to the switch from the source when it receives a membership report for group ff1e::2010 from one of the hosts—for example, Host B. If MLD snooping is not enabled on vlan100, the switch floods the multicast traffic on all interfaces in vlan100 (except for interface ge-0/0/12). If MLD snooping is enabled on vlan100, the switch monitors the MLD messages between the hosts and router, allowing it to determine that only Host B is interested in receiving the multicast traffic. The switch then forwards the multicast traffic only to interface ge-0/0/1.

This example shows how to enable MLD snooping on vlan100. It also shows how to perform the following optional configurations, which can reduce group join and leave latency:

  • Configure immediate leave on the VLAN. When immediate leave is configured, the switch stops forwarding multicast traffic on an interface when it detects that the last member of the multicast group has left the group. If immediate leave is not configured, the switch waits until the group-specific membership queries time out before it stops forwarding traffic.

  • Configure ge-0/0/12 as a static multicast-router interface. In this topology, ge-0/0/12 always leads to the multicast router. By statically configuring ge-0/0/12 as a multicast-router interface, you avoid any delay imposed by the switch having to learn that ge-0/0/12 is a multicast-router interface.


To configure MLD snooping on a switch:


CLI Quick Configuration

To quickly configure MLD snooping, copy the following commands and paste them into the switch terminal window:

Step-by-Step Procedure

To configure MLD snooping:

  1. Enable MLD snooping on the VLAN vlan100:

  2. Configure the switch to immediately remove a group membership from an interface when it receives a leave report from the last member of the group on the interface:

  3. Statically configure interface ge-0/0/12 as a multicast-router interface:


Check the results of the configuration:

Verifying MLD Snooping Configuration

To verify that MLD snooping is enabled on the VLAN and the MLD snooping forwarding interfaces are correct, perform the following task:

Verifying MLD Snooping Interface Membership on VLAN vlan100


Verify that MLD snooping is enabled on the VLAN vlan 100 and that the multicast-router interface is statically configured:


Show the MLD snooping information for ge-0/0/12.0:


MLD snooping is running on vlan100, and interface ge-0/0/12.0 is a statically configured multicast-router interface. Immediate leave is enabled on the interface.