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Re: [Xen-devel] [PATCH]: xl: use libuuid to generate random UUID's

To: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Subject: Re: [Xen-devel] [PATCH]: xl: use libuuid to generate random UUID's
From: Ian Campbell <Ian.Campbell@xxxxxxxxxx>
Date: Tue, 10 Aug 2010 11:44:46 +0100
Cc: Ian Pratt <Ian.Pratt@xxxxxxxxxxxxx>, Xen Devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>, "Gianni Tedesco \(3P\)" <gianni.tedesco@xxxxxxxxxx>, Stefano Stabellini <Stefano.Stabellini@xxxxxxxxxxxxx>
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On Thu, 2010-08-05 at 03:27 +0100, Jeremy Fitzhardinge wrote:
> On 08/04/2010 07:19 PM, Ian Pratt wrote:
> > The best approach is to generate locally administered MAC addresses
> hence giving us 46 bits of freedom rather than XenSource registered
> OUI addresses which have just 24 bits -- collisions will be *much*
> less likely. Further, it's best not to generate random addresses every
> time, but to derive the MAC address from a good hash of the VM UUID
> and the NIC number so that they are deterministic.
> Yes!  I've been doing that manually (where my hash is '+'), but its 
> irritating to keep doing over and over.

Where I care about a stable MAC I use
        vif = [ 'mac=xx:xx:xx:xx:xx:xx' ]
in my domain config file. AFAICT that is the only 100% reliable way to
get a stable MAC address since the other schemes all have some corner
case or other...


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