Hi Klaus, thanks for your reply.
So are you saying that the best way to support multicast in a VBOX environment is to use the bridging configuration for my VM's network cards, and if I do that, then all multicast is passed into VMs? Or does it actually do something smarter like IGMP filtering?
If I want to receive multicast in my VM, then it (or better: my application inside the VM) would normally register on IP multicast addresses via IGMP. On a non-virtualized system, the network card of the machine would be switched into multicast listening mode and would only register on that particular address (at Ethernet level) to pass packets to that address up to the host OS. It would not go into promiscous mode. And multicast packets to other addresses I didn't register for, will be dropped.
If I now have a VM environment, then how do I get the host NIC to register for multicast addresses my VMs are interested in? Does that work with VBOX? Or will, with bridging, the host NIC be set into all promiscous mode by default? That seems to be a performance hit. Will it pass ANY multicast packets into my VM and not do any sort of filtering at all, I guess?
Thanks for your help.
Karoline
Klaus Espenlaub <klaus.espenlaub at oracle.com> schrieb am 13:35 Donnerstag, 10.Juli 2014:
Karoline
Post by Karoline HausDo the host-only network interfaces in any way behave differently to the
typical tun/tap Ethernet devices Linux offers? I mean in terms of
multicast reception. So if I bridge from the physical device to the
host-only interface then it should be able to process multicast pakets
as well right?
It should - but why would one want to touch the linux bridging support?
The reason why we dumped it years ago was that it was extremely
unreliable. Caused random connectivity problems, and there were setups
where for unexplainable reasons no data would ever pass through br0 to
the tap device used by VirtualBox. Of course it might be all fixed by
now, but using linux bridging to connect to a host only network sounds
like a very complicated way to replace VirtualBox bridging straight to
the desired interface.
There is no intentional multicast blocking done anywhere in VirtualBox.
Klaus
Post by Karoline HausKaroline,
? > Hi there, I was just wondering, if it was possible to control multicast
? > reception for VMs via host-only interfaces via the VBOX API? I could not
? > find anything but not sure I searched in the right place. Thanks for any
? > pointers!
There's nothing in the API controlling this, and the reason is that the
emulation itself deals with ethernet frames. It couldn't care less what
they mean. Of course the actual behavior heavily depends on the
networking mode (NAT definitely doesn't handle multicast in a sensible
way), and bridged/host only/internal network should be able to handle
them. Theoretically. Not aware of this getting tested :)
Klaus
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