TAP tunnels and multicast traffic

[Damien Miller]

On Tue, 30 Jan 2018, Tom Cook wrote:

> I then start the vendor's software and ask it to discover the remote
> equipment.  This fails and, at the same time, my python script on the
> laptop stops working.  I can still ping remote addresses from both the
> laptop and the VM, but multicast UDP across the link no longer works.  Even
> if I shut down the VM, the tunnel is still working for 'normal' IP traffic
> is still working but the multicast UDP discovery doesn't work any more.

You could start by diffing the routing table on the Windows VM before
and after the vendor software runs, and/or running tcpdump or wireshark
to see what it's trying to do. Also consider running tcpdump on the
intermediate hops to see whether the multicast packets are propagating
as you'd expect.

-d