netdev - Re: What makes a good fake MAC address?

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Date:	Wed, 22 Apr 2009 15:59:09 -0700
From:	Stephen Hemminger <shemminger@...tta.com>
To:	Inaky Perez-Gonzalez <inaky@...ux.intel.com>
Cc:	Mark Smith <ipng@...06e6720323030352d30312d31340a.nosense.org>,
	netdev@...r.kernel.org
Subject: Re: What makes a good fake MAC address?

On Wed, 22 Apr 2009 15:38:10 -0700
Inaky Perez-Gonzalez <inaky@...ux.intel.com> wrote:

> On Wednesday 22 April 2009, Stephen Hemminger wrote:
> > On Wed, 22 Apr 2009 15:15:05 -0700
> >
> > Inaky Perez-Gonzalez <inaky@...ux.intel.com> wrote:
> > > On Wednesday 22 April 2009, Mark Smith wrote:
> > > > Hi Inaky,
> > > >
> > > > (please CC me, I'm not on the list)
> > > >
> > > > "The problem with using a zero mac address is that it confuses
> > > > the bridging software (and maybe others). I was wondering, what
> > > > would be a fake mac address we could put in there that is legal
> > > > for this kind of "faking"? [or the closest thing to legal?]"
> > > >
> > > > Since you're from an organisation with an OUI allocation or
> > > > two, I think a real Intel one would be best. It then wouldn't
> > > > be fake, and no matter where it was exposed (host only, local
> > > > network, or globally e.g. in IPv6 node addresses), it would be
> > > > guaranteed not to collide with any other addresses (unless
> > > > Intel make error an error in their own OUI administration.)
> > >
> > > It doesn't really work, because it is for the "from" end of the
> > > connection; as said somewhere else in the thread, the WiMAX link
> > > is P2P, IP only. The card has a local address, that we use for
> > > the "to" field, but for the from, we need to fake an address from
> > > the network -- which is not necessarily an intel device :)
> > >
> > > So maybe local addresses would not be the right choice, and
> > > clearly Intel assigned ones neither :)
> >
> > You need a from address for the bridge to be able to populate its
> > forwarding table. If remote end is always same, just get some random
> > address at start of tunnel and reuse it.
> 
> Nope, the remote end will change as you move around from base station
> to base station :(
> 

Then don't bridge.
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