Learn how **IGMP snooping** and **multicast filtering** prevent network flooding in Dante, AES67, and NDI broadcast environments.
Essential for maintaining stable IP media fabrics. For specific switch configurations, use our network switch configurator. Explore more broadcast engineering tools for IP video and media networking.
In a standard IT network, data is usually transferred via Unicast—a direct one-to-one conversation between a sender and a receiver. But in a broadcast environment, you often need to send one camera's video feed to five different monitors, or one microphone's audio channel to three different mixing consoles simultaneously.
Sending five separate Unicast streams of the same 150 Mbps NDI video feed would immediately choke the source device's network interface limit. The solution is Multicast. The sender broadcasts a single stream to a specific IP address (e.g., 239.255.0.1), and any device that wants to see the video simply "subscribes" to that address.
However, basic, unmanaged network switches do not understand Multicast subscriptions. When a "dumb" switch encounters a Multicast packet, it panics and treats it like a Broadcast packet—duplicating the 150 Mbps video stream out of every single port on the switch. If you attach a 10 Mbps control surface or a wireless access point to that switch, it will be instantly flooded with video data and crash. This is known as Multicast flooding.
To prevent this catastrophic network collapse, Managed (Layer 2) and Layer 3 Ethernet switches use a protocol called IGMP Snooping (Internet Group Management Protocol).
When IGMP Snooping is enabled, the switch actively "listens" (snoops) on the conversations between the devices to see who is requesting to join or leave a Multicast group. The switch builds an internal roadmap—a Multicast forwarding database.
IGMP Snooping by itself is a passive feature. The switch only listens to "Join" commands. But what happens if a device is restarted, or the switch rebooted? The switch forgets who wants what, and the Multicast stream stops routing.
This is why you absolutely must configure an IGMP Querier. The Querier is an active service (usually ticked on inside your core switch's settings) that periodically shouts out to the entire network: "Hey, who still wants to receive Multicast Group 239.255.0.1?"
The connected devices respond with their membership reports, keeping the switch's internal map updated. In a multi-switch AV network, you must ensure that only one single switch is elected as the active IGMP Querier for a given VLAN, usually the Core or highest-capacity router in the topology.
Dante networks, utilizing AES67 compatibility, often rely heavily on Multicast flows, particularly for PTPv2 clock synchronization packets. A misconfigured IGMP topology will result in Clock Drift (read our PTP Clocking Guide) or dropped audio frames, because switch ports will prioritize the overwhelming Multicast flood over priority audio streams.
For high-bandwidth NDI, the stakes are even higher. A single Full NDI 1080p60 stream requires roughly 125 Mbps. (Read the NDI Bandwidth breakdown here). Multicasting three cameras without an IGMP Querier on a 1GbE switch will mathematically saturate the backplane almost instantly, resulting in frozen video feeds and tearing across the entire production.