[ovs-discuss] Forwarding between Multiple interfaces Openflow

Ben Pfaff blp at nicira.com
Tue Mar 1 04:37:38 UTC 2011

On Mon, Feb 28, 2011 at 8:04 PM, Aaron Rosen <arosen at clemson.edu> wrote:
> Any idea what could be going on here:
> From I'm pinging (I've setup routes on the
> network so that packets get to the right end points)
> I have dp1 ( and dp0 ( on the same computer. If I
> run tcpdump on dp1 (which is the interface directly connected to the
> internet) I see these packets .
> 22:58:17.462526 IP > ICMP echo request, id
> 16684, seq 113, length 64
> 22:58:17.613943 IP > ICMP echo request, id
> 30764, seq 13, length 64
> Though If I run tcpdump at dp0 I don't see these packets nor do I get
> packet-in events for them. You said before that Open vSwitch isn't an IP
> stack so does that mean tcpdump isn't going to be working there? Any idea
> what I need to do to get packets to route between the two interfaces?
> Shouldn't the linux routing tables handle this or not at all?

tcpdump works on Linux network devices whether they have an IP address
configured or not, so that isn't the problem.

Do you want to do switching or routing between the two interfaces?  OVS is
a switch, not a router, so if you want to do routing, then OVS is not the
obvious choice, although it might usefully be a component of a solution.
If you do want to do switching, then the Linux routing table is not

If you want to set up a switch named br0 with interfaces eth0 and eth1,
then starting from a clean setup you can run:
  ovs-vsctl add-br br0
  ovs-vsctl add-port br0 eth0
  ovs-vsctl add-port br0 eth1

You haven't really said what setup you are currently using, unless I
missed it somewhere.  It sort of sounds like you have two separate
bridges, one of which contains one Ethernet interface and the other
of which contains the other.  That setup only makes sense if you are
doing routing or tunneling or something else to span between one bridge
and the other.

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