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From: Paul Brook <paul@codesourcery.com>
Subject: Re: [Qemu-devel] Connecting two tap interfaces to one qemu instance
Date: Fri, 29 May 2009 12:54:50 +0100
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To: qemu-devel@nongnu.org
Cc: Brian Jackson <iggy@theiggy.com>, Jedrzej Kalinowski <kalinoj1@iem.pw.edu.pl>

> Yes, I tried STP on bridge and it helps.
> But it's fighting effects, not cause of the problem
>
> My understanding is that qemu should not work like this. Usual host with
> two network devices connected to the same network doesn't create loops
> like this.

You aren't emulating a host with two devices. You're emulating a switch with 
three ports. One connected to the guest, and the other two connected to tap 
interfaces. Exactly the same thing will happen if you implement this topology 
with real hardware.

Paul