Re: [Qemu-devel] tap devices not receiving packets from a bridge

[Stefan Hajnoczi <stefanha@gmail.com>]

On Thu, Nov 22, 2012 at 03:29:52PM +0100, Peter Lieven wrote:
> is anyone aware of a problem with the linux network bridge that in very rare circumstances stops
> a bridge from sending pakets to a tap device?
> 
> My problem occurs in conjunction with vanilla qemu-kvm-1.2.0 and Ubuntu Kernel 3.2.0-34.53
> which is based on Linux 3.2.33.
> 
> I was not yet able to reproduce the issue, it happens in really rare cases. The symptom is that
> the tap does not have any TX packets. RX is working fine. I see the packets coming in at
> the physical interface on the host, but they are not forwarded to the tap interface.
> The bridge itself has learnt the mac address of the vServer that is connected to the tap interface.
> It does not help to toggle the bridge link status,  the tap interface status or the interface in the vServer.
> It seems that problem occurs if a tap interface that has previously been used, but set to nonpersistent
> is set persistent again and then is by chance assigned to the same vServer (=same mac address on same
> bridge) again. Unfortunately it seems not to be reproducible.

Not sure but this patch from Michael Tsirkin may help - it solves an
issue with persistent tap devices:

http://patchwork.ozlabs.org/patch/198598/

Stefan