RE: [Xen-users] uniq mac address generator

[Timo Benk <timo.benk@xxxxxx>]

On Fri, 13 Apr 2007 16:04:21 +0200, "Petersson, Mats" <Mats.Petersson@xxxxxxx> 
wrote:
>  
> 
>> -----Original Message-----
>> From: Timo Benk [mailto:timo.benk@xxxxxx] 
>> Sent: 13 April 2007 15:00
>> To: Petersson, Mats
>> Cc: trilok nuwal; Xen list
>> Subject: RE: [Xen-users] uniq mac address generator
>> 
>> On Fri, 13 Apr 2007 15:40:45 +0200, "Petersson, Mats" 
>> <Mats.Petersson@xxxxxxx> wrote:
>> >  
>> > 
>> >> -----Original Message-----
>> >> From: Timo Benk [mailto:timo.benk@xxxxxx] 
>> >> Sent: 13 April 2007 14:34
>> >> To: trilok nuwal
>> >> Cc: Petersson, Mats; Xen list
>> >> Subject: Re: [Xen-users] uniq mac address generator
>> >> 
>> >> Hi,
>> >> 
>> >> > But How i can insure that mac geneareted by this script will
>> >> > be uniq in whole world. Some body in the same network also
>> >> > might use the same script
>> >> > and can get the same  mac as i am .
>> >> 
>> >> You can add a little python to your config files. That way
>> >> you can bind the MAC to the vmid parameter. The vmid
>> >> code is directly extracted off the example configuration.
>> > 
>> > But that's CERTAINLY doesn't make it unique, unless you 
>> also make sure
>> > the rest of the numbers that make up the MAC address are 
>> unique to the
>> > world. I also think you need to restrict your VMID to 0..255 in some
>> > way, such as "and 255" or "modulo 256". [Don't know for 
>> sure how you do
>> > that in Python].  
>> 
>> Well, i don't think that the intention of the original author 
>> was to ensure
>> worldwide uniqueness.
>> 
>> But with the skript you can ensure unique MAC-Adresses inside 
>> you network.
>> 
>> By changeing the prefix you can run multiple Domain-0s, each 
>> with a uniq
>> MAC-Adress space.
> 
> Yes, but if you start/restart/save/restore/migrate your domain(s)
> sufficient number of times (and implement the modulo, otherwise you'll
> just end up with a "badly formed mac-address"), you'll have a collision
> every 256 VMid's. 

Why that?

I don't think that you will have 256 running domains, and if you have
such many domains, add another parameter, another prefix, whatever.

vmid is not equal to the domain id, but a new xm parameter.

Greetings,
-timo

-- 
Timo Benk - Jabber ID: fry@xxxxxxxxxxxx - ICQ ID: #414944731
PGP Public Key: http://www.m28s01.vlinux.de/timo_benk_gpg_key.asc



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