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Configuring IGMP Snooping on Switches

Internet Group Management Protocol (IGMP) snooping constrains the flooding of IPv4 multicast traffic on VLANs on a device. With IGMP snooping enabled, the device monitors IGMP traffic on the network and uses what it learns to forward multicast traffic to only the downstream interfaces that are connected to interested receivers. The device conserves bandwidth by sending multicast traffic only to interfaces connected to devices that want to receive the traffic, instead of flooding the traffic to all the downstream interfaces in a VLAN.

The default factory configuration on some switches enables IGMP snooping by default on all VLANs. In this case, you don’t need any other configuration for IGMP snooping to work. However, if you want IGMP snooping enabled only on some VLANs, you can either disable the feature on all VLANs and then enable it selectively on the desired VLANs, or simply disable the feature selectively on those where you do not want IGMP snooping. You can also customize other available IGMP snooping options.

Tip:

When you configure IGMP snooping using the vlan all statement (where supported), any VLAN that is not individually configured for IGMP snooping inherits the vlan all configuration. Any VLAN that is individually configured for IGMP snooping, on the other hand, does not inherit the vlan all configuration. Any parameters that are not explicitly defined for the individual VLAN assume their default values, not the values specified in the vlan all configuration. For example, in the following configuration:

all VLANs except employee-vlan have a robust count of 8. Because you individually configured employee-vlan, its robust count value is not determined by the value set under vlan all. Instead, its robust-count value is 2, the default value.

On switches without IGMP snooping enabled in the default factory configuration, you must explicitly enable IGMP snooping and configure any other of the available IGMP snooping options you want on a VLAN.

Use the following configuration steps as needed for your network to enable IGMP snooping on all VLANs (where supported), enable or disable IGMP snooping selectively on a VLAN, and configure available IGMP snooping options:

Platform-Specific IGMP Snooping Behavior

Use Feature Explorer to confirm platform and release support for specific features.

Use the following table to review platform-specific behavior for your platform.

Table 1: Platform-Specific IGMP Snooping Behavior

Platform

Difference

EX Series

  • The default factory configuration on some legacy EX Series switches enables IGMP snooping by default on all VLANs.

  • You cannot configure IGMP snooping on a secondary (private) VLAN (PVLAN). However, starting in Junos OS Release 18.3R1 on EX4300 switches and EX4300 Virtual Chassis, and Junos OS Release 19.2R1 on EX4300 multigigabit switches, you can configure the vlan statement at the [edit protocols igmp-snooping] hierarchy level with a primary VLAN, which implicitly enables IGMP snooping on its secondary VLANs and avoids flooding multicast traffic on PVLANs. See IGMP Snooping on Private VLANs (PVLANs) for details.
  1. To enable IGMP snooping on all VLANs :

    Or disable IGMP snooping on all VLANs:

  2. To enable IGMP snooping on a specified VLAN, for example, on a VLAN named employee-vlan:
  3. To configure the switch to immediately remove group memberships from interfaces on a VLAN when it receives a leave message through that VLAN, so it doesn’t forward any membership queries for the multicast group to the VLAN (IGMPv2 only):
  4. To configure an interface to statically belong to a multicast group:
  5. To configure an interface to forward IGMP queries it receives from multicast routers:
  6. To change the default number of timeout intervals the device waits before timing out and removing a multicast group on a VLAN:
  7. If you want a device to act as an IGMP querier, enter the following:

    The switch sends IGMP queries with the configured source address. To ensure this switch is always the IGMP querier on the network, make sure the source address is lower (a lesser number) than the IP addresses for any other multicast routers on the same local network.

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