Re: [Bridge] IP address on physcial interface instead of bridge interface?

[Stephen Hemminger <shemminger@linux-foundation.org>]

On Sat, 27 Mar 2010 11:50:23 +0100
Joakim Tjernlund <joakim.tjernlund@transmode.se> wrote:

> "richardvoigt@gmail.com" <richardvoigt@gmail.com> wrote on 2010/03/26 22:42:52:
> >
> > On Fri, Mar 26, 2010 at 3:48 PM, Joakim Tjernlund
> > <joakim.tjernlund@transmode.se> wrote:
> > >
> > >
> > > Nicolas de Pesloüan <nicolas.2p.debian@free.fr> wrote on 2010/03/26 21:39:33:
> > >
> > >> From: Nicolas de Pesloüan <nicolas.2p.debian@free.fr>
> > >> To: Joakim Tjernlund <joakim.tjernlund@transmode.se>
> > >> Cc: bridge@lists.linux-foundation.org
> > >> Date: 2010/03/26 21:39
> > >> Subject: Re: [Bridge] IP address on physcial interface instead of bridge interface?
> > >>
> > >> Joakim Tjernlund wrote:
> > >>
> > >> > Figure a small picture will help so here it is:
> > >> >
> > >> > Before adding eth0 to br0:
> > >> > eth0    br0
> > >> >  |
> > >> >  |
> > >> > HW controller
> > >> >
> > >> > after adding eth0 to br0:
> > >> > eth0
> > >> >   \
> > >> >    \
> > >> >      br0
> > >> >    /
> > >> >   /
> > >> > HW controller
> > >>
> > >> I don't understand your ascii art. What is HW controller ? eth0 is an hardware
> > >> controller !?
> > >>
> > >>    Nicolas.
> > >
> > > eth0 is the I/F IP stack will see/use. HW controller is the ethernet HW controller,
> > > the PCI HW if you like.
> >
> > No!
> >
> > br0 does NOT sit between eth0 and the NIC.  eth0 still represents the
> > NIC.  br0 sits on top, and represents the combined traffic stream from
> > eth0 and all other bridge ports.  By adding eth0 to the bridge, you
> > told it to forward all incoming frames to br0 which is the next higher
> > layer in the virtual interface hierarchy.
> 
> Of course the above isn't how the bridge works today. I was trying
> to described a new feature which would let me use eth0 as my normal
> IP interface even after it was added to the bridge.
> The above would emulate connecting the eth0 I/F to an external HW bridge.

If you read the network receive code path in the kernel, you
will see that there is a special hook used. Basically,

  if received_interface_is_part_of_bridge(incoming_interface)
  then process_bridged_packet(packet)

Then bridge looks at packet and decides whether it is local or forwarded.
The problem is with your application if it wants to use eth0 directly.




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