[ovs-discuss] tunnel between open vswitch on xenservers

terryxing xingtianyi at gmail.com
Sun Oct 2 05:44:54 UTC 2011


Dear Jesse,

Thanks for you reply. That makes sense.

I have one question,  you said

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.


Is open Vswitch a layer 2 switch ? Where is the routing table residing ? And
what can we do with that routing table ?

Thanks very much.

On Fri, Sep 30, 2011 at 3:45 PM, Jesse Gross <jesse at nicira.com> wrote:

> On Thu, Sep 29, 2011 at 11:11 PM, terryxing <xingtianyi at gmail.com> 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.
>



-- 
Best regards,

Tianyi Xing (邢天翼)

PhD Student, Research & Teaching Associate
SNAC:Secure Networking and Computing group
School of Computing, Informatics, and Decision Systems Engineering
Ira A. Fulton School of Engineering,
Arizona State University
Tempe, AZ 85281, USA
Cell: (+1) 480-678-3090
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