[Bridge] Bridge responds on its IP address even when br0 is down.

[Stephen Hemminger]

On Wed, 9 Jun 2010 18:30:17 +0200
Joakim Tjernlund <joakim.tjernlund at transmode.se> wrote:

> Stephen Hemminger <shemminger at linux-foundation.org> wrote on 2010/06/09 17:23:19:
> >
> > On Wed, 9 Jun 2010 16:46:01 +0200
> > Joakim Tjernlund <joakim.tjernlund at transmode.se> wrote:
> >
> > >
> > > System A:
> > > eth0 has ip 192.168.1.16
> > >
> > > Then do in system A
> > > brctl addbr br0
> > > ifconfig br0 192.168.1.18 down
> > >
> > >
> > > From system B I ping 192.168.1.18
> > > and system A responds!
> > >
> > > Even though interface br0 is down I can still
> > > access system A with 192.168.1.18, this feels
> > > like a bridge bug?
> > >
> >
> > No that is how Linux works. All addresses are property of the
> > system not the interface.
> >    http://en.wikipedia.org/wiki/Host_model
> 
> I see, I know the about the host model but I was surprised it applied
> to interfaces that is down. Does it not make sense to exclude the
> IP address when the I/F is down?

Responding on a all interfaces all the time does make sense on a multi-homed server
(which was the original Linux use case), but it does on a router.
There is a configurable value in to control it in Vyatta to handle that.  
The patch got rejected when submitted upstream because of the developers worries
about breaking existing applications.