MulticastProxy

MulticastProxy is a Windows Service that relays multicast traffic between two Layer 3 networks.

It is designed for environments where multicast discovery or application traffic must cross a routed boundary, but native multicast routing is unavailable, undesirable, or too complex for the use case.

The service works by:

1. listening for multicast traffic on one or more configured UDP ports,
2. forwarding the received packet to a remote peer over unicast UDP,
3. receiving the packet on the remote peer,
4. re-emitting it as multicast on the destination network,
5. optionally rewriting subnet references inside the payload when needed.

For troubleshooting, the repository also includes a desktop debug viewer that tails structured relay events from the service and shows:

• multicast packets received locally
• packets forwarded over the tunnel
• packets accepted or dropped on the tunnel receiver
• payload rewrites
• packets re-multicasted locally

When running as a Windows service, configuration is resolved from the executable directory rather than the service working directory, so the installed appsettings.json is used consistently in both service and interactive runs.

---

Project status

This repository currently focuses on a production-oriented design and implementation path for the service.

The intended target is:

• .NET 8
• Windows Service hosting
• configuration through appsettings.json
• Windows Event Log logging
• MSI-based installation and upgrades
• safe, maintainable production code rather than a one-off proof of concept

---

Use case

Some devices and applications rely on multicast traffic for discovery or communication on a local subnet. That traffic usually does not cross a Layer 3 boundary by default.

MulticastProxy provides a controlled relay model:

• multicast traffic is received locally
• the payload is tunneled to a remote instance using unicast UDP
• the remote instance re-emits it as multicast on the destination network

This makes it possible to bridge multicast-dependent traffic between two routed networks without implementing full multicast routing.

---

Key features

• Windows Service design
• support for one or more multicast UDP ports
• unicast tunnel between two peers
• optional payload subnet rewrite
• typed configuration with startup validation
• Windows Event Log integration
• support for explicit interface binding on multi-NIC systems
• production-friendly architecture with clear separation of concerns

---

Non-goals

This project is not intended to be:

• a full Layer 2 bridge
• a general multicast router
• an automatic self-updating agent
• a catch-all network proxy for arbitrary protocols

The focus is narrow and intentional: relay selected multicast traffic safely and predictably.

---

High-level architecture

Each instance performs the same role and is configured to point at its peer.

Example flow:

• Site A receives multicast traffic on a configured group and port
• Site A forwards the packet to Site B over unicast UDP
• Site B receives the packet on the tunnel port
• Site B optionally rewrites subnet references in the payload
• Site B re-emits the packet as multicast on its local network

This same pattern works in both directions.

For more detail, see:

• docs/architecture.md
• docs/configuration.md

---

Repository structure

.
├── AGENTS.md
├── README.md
├── docs
│   ├── architecture.md
│   ├── configuration.md
│   └── appsettings.example.json

/src
  /MulticastProxy.Service
    Program.cs
    appsettings.json
    /Options
    /Validation
    /Services
    /Protocol
    /Debugging

  /MulticastProxy.DebugViewer
    Program.cs
    MainForm.cs

/tests
  /MulticastProxy.Service.Tests