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

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

On Sun, 28 Mar 2010 17:19:13 +0200
Joakim Tjernlund <joakim.tjernlund@transmode.se> wrote:

> Nicolas de Pesloüan <nicolas.2p.debian@free.fr> wrote on 2010/03/26 22:35:40:
> >
> > Joakim Tjernlund a écrit :
> > >
> > > 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.
> >
> > I tested the following setup:
> >
> > # eth0 setup:
> >
> > ip addr add $IP dev eth0
> > ip link set up dev eth0
> > ip route add default via $DEF_ROUTE
> >
> > # bridge setup:
> >
> > brctl addbr br0
> > brctl setfd br0 0
> >
> > Then I tested the following migration sequence to move the IP addresse to br0:
> >
> > ip addr add $IP dev br0
> > ip link set up dev br0
> >
> > brctl addif br0 eth0
> > ip addr del $IP dev eth0
> > ip route add default via $DEF_ROUTE
> >
> > Thanks to "brctl setfd br0 0", this migration cause no trouble to active connections.
> >
> > So I cannot find a good reason to try and use eth0 as the "main" bridge interface.
> >
> > Do you have a process really linked to eth0 ?
> 
> So I did a quick test and it did seem to work for the simple case. However
> there may be other routes connected to eth0 than just the default route so
> one have to scan the whole route table. There is also the another problem,
> now the I/F is named br0 and all config/status ops related to eth0 must
> be changed to use br0 instead.
> The routing daemon(Quagga) also needs to update its config to use br0 instead.
> All in all, using br0 instead of eth0 works on a technical level but
> all apps dealing with routes and interfaces needs to be updated and this
> is not trivial nor wanted.
> 
> Allowing eth0 be used as I suggested would really help in these
> configurations. Would such a change be welcomed and is it
> hard to impl. ?

The bridge code is becoming a mess as everyone implements there favorite
rework. I prefer to have custom modifications handled by netfilter (the all purpose
packet patch kit). 

I am considering some patches to allow a "master interface" but this solves a different
issue, which relates to booting in virtual environments.

You can always rename interfaces.

ip li set dev eth0 name eth0_link
ip li set dev br0 name eth0




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