VLAN design and multicast control
Segmenting show traffic into VLANs and keeping multicast contained, so one chatty device cannot take the whole fabric with it.
What it is
A VLAN splits one physical switch fabric into separate broadcast domains. On a show network that usually means lighting control, tracking data, audio-over-IP, video, and management each get their own domain, with a deliberate decision about where the layer 3 boundary sits and what is allowed to cross it. Multicast is the other half of the same problem. sACN, PSN, OTP and most audio-over-IP transports send one stream to a group address and let the network replicate it. Switches flood multicast to every port in the domain unless IGMP snooping is enabled and an IGMP querier is present on that VLAN to keep group membership alive. The design work is deciding which traffic classes share a domain, and which device owns the querier on each one.
Why it matters
A flat network with unmanaged multicast works fine on a bench with four devices and fails in a loaded venue, which means it fails after the design is frozen and the truck has left. The failure modes are ugly and intermittent: a console that stutters only when the video department powers up, a tracking feed that drops packets on one rack because a switch uplink is saturated with traffic nothing on that rack asked for, a device that renegotiates its link and quietly floods a domain. Across eight shows a week, the version that matters is not whether the network passed a quiet afternoon test but whether it degrades predictably when someone adds a device, swaps a switch, or patches the house network into yours at the worst moment.
IGMP snooping without an active querier degrades to flooding or to dropped groups, depending on the switch
One querier per VLAN with a deterministic winner, rather than several devices quietly electing one
Keep discovery-heavy and broadcast-heavy traffic off the domain carrying real-time position data
Routing multicast between VLANs takes an explicit multicast design, not just an interface with an IP on it
Do we actually need VLANs on a small rig?
It depends on what shares the fabric and how it will grow. A handful of devices on dedicated switches with no other traffic can run flat. The moment lighting, tracking, audio and a house network share physical infrastructure, segmentation is what keeps one department from being able to affect another. It also makes fault isolation possible, which matters more than throughput on most shows.
Where should the IGMP querier live?
On a device that is always powered, always present, and under your control, configured explicitly rather than left to election. Querier election picks a winner by address, so an unmanaged device joining the domain can take the role and change behavior with no visible cause. Set the querier on the core switch for each VLAN carrying multicast, confirm which device is actually serving it, and record that in the handover.
IGMPv2 or v3?
Version support in entertainment gear is uneven, and a good deal of it implements v2 only. A querier configured for v3 exclusively can leave those devices without a working join. The safe move is to check what every multicast consumer on that VLAN supports before choosing, and to verify group membership on the switch rather than assuming the join succeeded because the stream looked right at first.