[ovs-discuss] why ovs it does not ask the controller

Ben Pfaff blp at nicira.com
Sat May 2 16:57:50 UTC 2015

I noticed that you mentioned wireless.  Are you sure that isn't the
problem?  The FAQ says:

### Q: I can't seem to use Open vSwitch in a wireless network.

A: Wireless base stations generally only allow packets with the source
   MAC address of NIC that completed the initial handshake.
   Therefore, without MAC rewriting, only a single device can
   communicate over a single wireless link.

   This isn't specific to Open vSwitch, it's enforced by the access
   point, so the same problems will show up with the Linux bridge or
   any other way to do bridging.

On Sat, May 02, 2015 at 01:58:36PM +0900, Minh Nghiem Gia wrote:
> Thanks Ben for your confirmation.
> I used wireshark to capture packets on the bridge br0 and physical wlan NIC
> (wlan0).
> I executed a simple ping from the PC to the gateway. No arp cache so I only
> saw arp request for the gatway. when OVS still has normal rule, I saw the
> arp packet on both br0 and wlan0. When I deleted all flow rules, I did not
> see arp on the bridge but saw arp on the wlan0.
> Could you tell me why there is no flow rule, the packet can reach wlan0? I
> mean should the OVS drop the packet? Or do arp packets not go through the
> switch? And is there any ways to debug/capture this behavior (i.e., OVS
> communicate with the system via netlink? The system sends out arp packets?)
> Best regards,
> Minh.
> 2015-05-01 23:33 GMT+09:00 Ben Pfaff <blp at nicira.com>:
> > On Fri, May 01, 2015 at 03:51:07PM +0900, Minh Nghiem Gia wrote:
> > > I have a simple question, however I could not find any way to answer is
> > > "why ovs has no rules, it does not ask the controller". In theory, when a
> > > new packet comes, if there is no matching found, the switch will ask the
> > > controller for actions. In fact, I can see the Packet_in message if I use
> > > mininet to connect to a controller on a different PC.
> > > What I did is I installed both controller and OVS on the same PC which
> > has
> > > multiple network interfaces act as ports of OVS. Then I deleted all flow
> > > rules on the switch (sudo ovs-ofctl del-flows br0) and executed a ping
> > from
> > > that PC to the gateway. I think the switch must ask the controller, but
> > > there is no OF messages!
> >
> > OVS should work the same way in the second case as in the first.  OVS
> > doesn't know whether the controller is on the same PC or a different
> > one.
> >

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