[libvirt-users] Domain XML Multicast Tunnel

Daniel P. Berrangé berrange at redhat.com
Mon Dec 2 11:58:04 UTC 2019

On Sat, Nov 30, 2019 at 03:59:54PM +0000, Richard M wrote:
> Hello
> I found under networking in the Domain XML 'Multcast tunnel'.
> My question is does anyone know what is the intended use of multicast
> tunnel networking?What are the potential pitfalls of using such a
> configuration other than what's highlighted in the domain xml. eg:
> can it suffer from throughput issues? Can the tunnel be accessed from
> outside Libvirt?
> I'm struggling to find any information about it. If anyone has any
> information about it, Or where I can obtain such information it would
> be appreciated.

This is something that has been supported by QEMU forever, but I think
it is fair to say it is rarely used.

The main use case would be setting up network communication between
a group in QEMU instances (possibly across hosts) in a case where you
don't have access to any better technology such as tap device + bridging.
eg if you are an unprivileged user & cannot get root.

I doubt performance is going to be anything special. There's also
no meaningful security - any user or process or host can send &
receive on the same multicast address.

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