[Bridge] RE: [Xen-devel] nfsroot and brige (fwd)

Stephen Hemminger shemminger at osdl.org
Thu Jan 13 11:17:33 PST 2005

On Wed, 12 Jan 2005 16:40:25 -0500 (EST)
Adam Sulmicki <adam at cfar.umd.edu> wrote:

> any comments?
> if nothing else, is there any way to atomically setup bridge?
> not on list, please cc.
> ---------- Forwarded message ----------
> Date: Wed, 12 Jan 2005 21:08:15 -0000
> From: Ian Pratt <m+Ian.Pratt at cl.cam.ac.uk>
> To: Adam Sulmicki <adam at cfar.umd.edu>, xen-devel at lists.sourceforge.net
> Subject: RE: [Xen-devel] nfsroot and brige
> > hello,
> >  	it seems like a catch-22 to me. I boot xen0 with nfsroot,
> >  	and then try to setup bridge stuff. something like this
> >
> > /sbin/brctl addbr xen-br0
> > /sbin/brctl addif xen-br0 eth0
> > /sbin/ifconfig xen-br0 netmask up
> > /sbin/ifconfig eth0 promisc up
> >
> >  	however, once I start it running it crashes down with error
> >  	that nfs server is not available.
> >
> >  	does it mean that I must use initramfs to configure bridge
> >  	first, or is there some other way?
> It really bugs me that there's no atomic way to configure a bridge and
> transfer an IP address already active on another interface to it. I'm
> not 100% convinced that the current behaviour is actually what the
> bridge code author's intend: a the host can still transmit packet's with
> an IP associated with an eth interface that is part of a bridge, it just
> can't receive packets on that IP. I'd certainly appreciate it if someone
> could ask the question on the bridge mailing list...
> The workarounds for using nfsroot in dom0 at the moment are: a) use a
> ramfs to configure the bridge; b) use a routed rather than bridged
> setup.
> I'm actually going off the whole idea of bridging rather than routeing
> as the default...
> Ian

It wouldn't be that hard to write a small command that does the ioctl's
you need to setup the bridge and ip addresses at one time.  To just
create a bridge, add interface and move the IP address would be relatively

Or just put brctl and ifconfig in a ram filesystem (like initrd).

Stephen Hemminger	<shemminger at osdl.org>

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