Linux Ethernet Bridging - Jun 2010 - [Bridge] Bridge responds on its IP address even when br0 is down.

System A:
eth0 has ip 192.168.1.16

Then do in system A
brctl addbr br0
ifconfig br0 192.168.1.18 down

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

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?

        Jocke

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.