Re: [Qemu-devel] tun/tap networking

[Oliver Gerlich <olig9@gmx.de>]

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Jim C. Brown schrieb:
> On Fri, Sep 30, 2005 at 03:13:21PM -0700, Don Kitchen wrote:
> 
[...]
> 
>>I'm interested in the handling of ethernet frames because I haven't been
>>able to get the bridge to pass packets between added interfaces (yes,
>>they're all up and promisc) and I'm not too thrilled with networking being
>>bridged anyway,
> 
> 
> Do you mean the kernel bridge, br0? Or are you talking about some sort of
> user space bridge, like bridged (which uses a series of packet sockets to
> bridge between multiple ethernet (ethX) devices) ?
> 
> 
>>and it seems to me that if an fd were hooked up to a
>>BPF capturing everything from the real ethernet device in promiscuous
>>mode, and pushing out any raw frames it receives, that I could bypass
>>the bridge and make it as if the emulator's virtual ethernet device is
>>a real one. Or is there some reason this won't work? (after all, other
>>products don't have this, there must be a reason right?)
> 
> 
> Ah, you're talking about using a packet socket, right?
> 
> That works fine for the most part. There is one thing that you have missed
> though: guest->host communication doesn't work when you do that.
> 
> When you push out a raw frame, it leaves the real ethernet device before the
> host sees it. So guest->host doesn't work. You need to find another way to
> send packets from the guest to the host. Most host OSes will not let you
> do this at all. (Windows seems to be the exception, winpcap's pcap_sendpacket()
> appears to work fine for that job.)
> 

That means it would work if the host NIC is connected to a switch? Then
the switch would send packets from the guest which are meant for the
host back to the host NIC and everything's fine! Or did I misunderstand
that now?

Regards,
Oliver Gerlich
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