Introducing Cast — a multicast network testing tool for engineers who need answers, not guesswork

Verify IGMP snooping behaviour, probe switch group limits, and capture live multicast traffic — all from a single desktop app.

Multicast networks are notoriously opaque. When something breaks — traffic not forwarding, groups silently dropped, a switch behaving unexpectedly under load — the diagnostic process tends to involve a patchwork of CLI tools, protocol analysers, and a fair amount of intuition. We built Cast to change that.

Cast is a desktop application purpose-built for testing and monitoring multicast networks. Whether you're commissioning a new AV-over-IP deployment, stress-testing a managed switch before it goes into production, or hunting down a forwarding anomaly in an existing network, Cast gives you the tools to work systematically.

What's included

Switch Tester — Find your switch's group limit

Incrementally joins groups across two NICs, uses binary search to identify the exact IGMP snooping table capacity, and reports leave/rejoin behaviour and latency stats. Results can optionally be published to a community leaderboard for benchmarking against similar hardware.

Endpoint Tester — Monitor device IGMP behaviour live

See in real time which groups each device joins or leaves, which IGMP version it reports, and whether it responds correctly to querier messages.

Distributed Tester — Multi-machine reachability testing

A commander node orchestrates remote agents across interfaces to verify that multicast traffic reaches every segment of your network simultaneously — without requiring manual coordination between machines or sessions.

Receiver — Capture, inspect, and replay traffic

Capture live multicast on any interface. Inspect packets with a hex dump and UTF-8 decoder, filter by group or source, save sessions to disk, and replay them on demand. Useful for reproducing issues in a lab environment without the original source device.

Transmitter — Send test packets with precision

Single-shot or interval-based transmission to one or more groups. Supports plain text and raw hex payloads. Protocol presets for Dante, AES67, NDI, sACN, PTP, mDNS, and SSDP. Can replay saved recordings directly from the Receiver.

A few things worth highlighting

The Switch Tester is the feature most often reached for during commissioning work. It's not enough to know that a switch supports IGMP snooping — you need to know where it breaks under real load. Cast joins groups incrementally from a sender NIC while a listener NIC confirms forwarding; when drops appear, a binary search narrows in on the exact limit.

The Receiver and Transmitter are designed to work together. Capture a production session, save it, then replay it in a lab environment to reproduce an issue precisely — without needing the original source device on the network.

For larger networks, the Distributed Tester addresses a gap that single-machine tools can't fill. Verifying end-to-end multicast reachability across VLANs and routed segments typically requires coordination between multiple people or multiple sessions. Cast centralises that into a single test run, orchestrated from one machine.

Requirements

• IGMP snooping must be enabled on the switch under test.

• An IGMP querier must be running on the network.

• The Switch Tester requires two separate network interfaces — one for sending, one for listening.

Download

Cast is available now for macOS, Windows, and Linux. Download the package for your platform from the releases page and open it to install.