---
title: "Multicast"
slug: "multicast"
updated: 2025-12-19T19:59:01Z
published: 2025-12-19T19:59:01Z
canonical: "docs.swxtch.io/multicast"
---

> ## Documentation Index
> Fetch the complete documentation index at: https://docs.swxtch.io/llms.txt
> Use this file to discover all available pages before exploring further.

# Multicast

> [!NOTE]
> WHAT TO EXPECT
> 
> In this article, users will learn what is Software Defined Multicast and how it works in a cloudSwXtch environment.

### Multicast

Software Defined Multicast (SDMC™) is a feature of the **cloudSwXtch** overlay network. With SDMC, existing applications and services that expect standards-based, IP multicast traffic will work **without requiring any code changes** and with performance that approaches that of bare metal.

At a high level, **cloudSwXtch** implements a ***software switch*** that serves the same role as a hardware switch. **cloudSwXtch** receives multicast packets from producers and sends a copy of each packet to every subscribed destination. The **cloudSwXtch** control plane utilizes the industry-standard IGMPv2/3 specification for managing group membership.

The **xNIC** service handles multicast traffic between the switch and the VM operating system. The xNIC service must be installed on every VM that needs to send or receive multicast traffic on the cloud.

SUMMARY

The **cloudSwXtch** system consists of a software switch instantiated within a virtual network and a set of virtual machines that have an xNIC virtual interface. Optionally, users can connect their on-prem network to the cloudSwXtch and agents using a swXtchBridge.

Applications can send and receive IP multicast by targeting the virtual network interface. IGMP control packets are generated by the local operating system, and the xNIC virtual interface seamlessly picks these up and sends them to the **cloudSwXtch** instance. Local applications will work in this environment just as they would on a similar bare-metal network.

### Source Specific Multicast

Source Specific Multicast, or SSM, as defined by IGMPv3, is a method for delivering multicast packets in which the only packets that are delivered to the receiver are those originating from a specific source address requested by the receiver. Not only does this improve security within the cloudSwXtch, but it also alleviates strain on the network since the sender will know to only send a multicast stream from the specified single source and not via other source addresses.

This feature can be tested using `swx-perf`, a cloudSwXtch-based tool for generating and consuming synthetic traffic, as well as external applications that support SSM. For more information on testing SSM, please see the [swx-perf](/v2/docs/swxtch-perf) article under Testing cloudSwXtch.