On Thu, Sep 29, 2011 at 11:11 PM, terryxing <[email protected]> wrote:
> Dear Jesse,
>
> Thanks very much for your timely reply.  It works. But I have some confusion
> about the concept.
>
> I assign public ip for xenbr0 on each host, and private ip (172.16) for
> xenbr1 on each site.
>
> On Xenserver Host 1
> ovs-vsctl add-port xenbr1 gre1 -- set interface gre1 type=gre
> options:remote_ip=129.X.X.X (public ip address on xenbr0  of xenserver host
> 2)
> On Xenserver Host 2
> ovs-vsctl add-port xenbr1 gre1 -- set interface gre1 type=gre
> options:remote_ip=198.X.X.X (public ip address on xenbr0  of xenserver host
> 1)
>
> Note that we add gre port onto Xenbr1 but we use the ip of xenbr 0 as the
> remote accessible ip.  I attached the vif onto the xenbr1 so that VMs on two
> xenserver hosts can ping each other. It seems like the tunnel is established
> between two Xenbr1 but they talk to each other through the public ip on
> Xenbr0.   So, when packet sent from VM1, the packet will go from VIF to
> Xenbr1, then will the packet pass from xenbr1 to xenbr0 since it has to go
> through the public ip and internet to arrive at Xenserver host 2, right ?

Yes.

> So, my final question is, how xenbr1 know that  it has to forward this
> packet to xenbr0, and how these two xenbr1 and xenbr0 are connected ?

The routing table determines the interface that is used to output an
IP packet (including GRE), regardless of whether that interface is a
bridge or not.

> Also, what are the gre tunnel established between ? Xenbr1 to Xenbr1 ? or
> Xenbr0 to Xenbr0 ?

The interfaces on xenbr1 are connected by the tunnel, xenbr0 is the
transport network.
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