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Re: [Qemu-devel] network fails on windows

From: Derek Fawcus
Subject: Re: [Qemu-devel] network fails on windows
Date: Sat, 17 Jul 2004 22:52:40 +0100

On Sat, Jul 17, 2004 at 05:07:40PM +0200, Matthias Jung wrote:
> I was just on the verge of giving up until i tried one last thing:
> I switched the mac address parameter. Til then I had used the mac  
> a3:b2:23:54:7e:cf which is a valid mac

What do you mean 'valid'? - all values are 'valid'.

> and windows did detect the interface 
> without flaws, but no network access was possible.
> With 00:ff:7f:fc:36:d2 it suddenly worked, I only can imagine a bug in the 
> ne2000 windows driver, or in windows (95,98,2000 tested) itself, not allowing 
> such a mac. 

Well there would appear to be an important difference between those two MACs,
one is multicast,  one is unicast.

The first two bits of the MAC address (as transmitted on the wire) are the
group/unicast bit followed by the local/global bit.  These generally translate
into bits 0 and 1 of the first byte of the MAC address when written as above.

So the first address has A3 - which is multicast and local,  whereas the
second address has 00 which is unicast and global.  You may want to try
the first address again but with the first byte replaced as follows:

   a2 - A local unicast address
   a0 - A global unicast address


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