Re: [Xen-devel] Re: nfsroot and brige

[Adam Sulmicki <adam@xxxxxxxxxxxx>]

any chance to have generalized version of this in User's Manual? i think 
many ppl would find this usefull.
On Fri, 14 Jan 2005, Grzegorz Milos wrote:

> > > Instead use routing and iptables (masquerade) as follows:
> > > dom0 eth0 stays with 10.128.107.187
> > > dom0 eth1 stays with 192.168.0.65
> > > dom0 acts as a NAT for unpriviledged domains
> > that's what I was kind of figuring I would need to do.
> >
> > But a real bridge (I used to use them) would transparently bridge packets
> > from vif1.0 to eth1, right? This is what I never saw working, unless I did
> > things that made no sense (e.g. ifconfig xen-br0 192.168.0.65), and even
> > then I only got from domU to dom0. (it makes no real sense to me for a
> > *bridge* to have an IP address).
> > I would expect something working as a real bridge to allow me to do this:
> >
> > ifconfig eth1 192.168.0.65
> > brctl  xen-br0 addif eth1
> > brctl  xen-br0 addif vif1.0
> I am suprised that does not work. This is roughly what we are doing here. Let
> me just go through the steps you need to do to set up the bridge - maybe that
> will clarify something:
>
> a) create the bridge:
> brctl addbr xen-br0
> ifconfig xen-br0 up
>
> b) add the ip address of eth1 to the bridge (can also do it with ifconfig, but
> ip is easier to use):
> ip addr add 192.168.0.65 brd 10.212.4.255 scope global dev xen-br0
>
> c) setup routing:
> route del -net 192.168.0.0/24 eth1
> route add -net 192.168.0.0/24 xen-br0
>
> d) add eth1 to the bridge:
> brctl addif xen-br0 eth1
>
> The above sets up the bridge, then upon domain creation:
> e) add virtual interface to the bridge:
> brctl addif xen-br0 vif1.0
> ifconfig vif1.0 up
>
> That is all implemented in the two network scripts:
> /etc/xen/scripts/network
> /etc/xen/scripts/vif-bridge
>
> So if you decide not to use them make sure to have them disabled.
>
> All that should allow your unpriviledged domains to appear as if they were
> connected to your local network (through a switch or whatever else).
>
> In order to allow domU to access the internet you will have to:
> a) set up routing on domU:
> route add default gw 192.168.0.65
>
> b) set dom0 to work as a NAT
> iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
>
>
> Get back to me if that still does not work.
>
>
> > This is essentially wiring the two ifs up to xen-br0.
> >
> > then I dhcp from domU and I would think packets ought to flow to
> > vif1.0->eth1, and eth1->vif1.0, broadcasts would flow across the bridge
> > transparently and, once the right MAC discovery happened, packets from
> > vif1.0 would make it to 192.168.0.1
> >
> > I'm still not sure they didn't -- tcpdump seemed to think the DHCP
> > requests were going to eth1, but my home router didn't seem to think it
> > was seeing them. I will do a little more fooling around.
> >
> > ron
> Cheers
> Gregor

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