RE: [Xen-users] uniq mac address generator

["Petersson, Mats" <Mats.Petersson@xxxxxxx>]

> -----Original Message-----
> From: Timo Benk [mailto:timo.benk@xxxxxx] 
> Sent: 13 April 2007 15:16
> To: Petersson, Mats
> Cc: trilok nuwal; Xen list
> Subject: RE: [Xen-users] uniq mac address generator
> 
> 
> 
> 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.

Ah, ok, that explains something I hadn't caught on to (I'm by far not an
expert on the xm-level of Xen). 

Having more than 256 VM's on the same machine is probably pretty rare
indeed. 

--
Mats
> 
> 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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