[ovs-discuss] OVS sends ARP request to the controller also broadcasts ARP request

[Ben Pfaff]

The way you describe the problem confuses me.  As I read your
description, when OVS processes an ICMP packet, it forwards an ARP
packet to the controller.  OVS processes one packet at a time in an
almost-stateless way, so this is not really possible: as OVS processing
an ICMP packet, it only chooses how to deal with that ICMP packet; it
cannot easily influence the processing of ARP packets.

On Sat, Apr 14, 2018 at 01:50:12PM -0400, Sh j wrote:
> Thank you very much for your helpful explanation.
> 
> 
> I have another question.
> 
> When a ping packet is generated from node1 to node3 (the mentioned
> topology), in the next step, OVS1 is supposed to check its own flow table
> to see if there are any flow rules for this ICMP(IP) packet, and since the
> default flow rules installed by the controller tells that send the packet
> to the controller, the next packet_in message should include ICMP message.
> 
> But instead of that OVS1 forwards ARP request in the packet_in message. I
> am confused about this part. When I trace the packet, the action is sending
> to the controller. But somehow OVS1 skips this ICMP messages and goes to
> the ARP.  I suppose sending ARP happens when nodes know they are in one-hop
> neighbors. But in this case, nodes do not know the flow rules (routing path
> and next hop) and have to send packet_in (ICMP) to the controller. I do not
> know why these ARP are generating.
> 
> I am using CORE emulator to emulate this network. So I think I should check
> the Linux Kernel.  Could you let me know if you have any suggestion about
> the configuration?
> 
> Thank you
> 
> On Tue, Apr 10, 2018 at 6:27 PM, Ben Pfaff <blp at ovn.org> wrote:
> 
> > I think there's some confusion here.  OVS doesn't originate ARP
> > requests.  It only forwards ARP requests generated by some other
> > software, such as the Linux kernel.  If you don't want OVS to pass ARP
> > requests to the controller via packet_in, then you can either configure
> > the software that generates them not to do so, or you can configure OVS
> > (via the controller) to forward them without generating a packet_in.
> >
> > On Tue, Apr 10, 2018 at 05:54:36PM -0400, Sh j wrote:
> > > Thank you. I fixed the problem through the flow table installed by ONOS
> > and
> > > I do not see ARP broadcasts anymore.
> > >
> > >
> > >
> > >
> > > I have another question about packet_in messages to the controller.
> > Before
> > > that, I will explain about my topology. I asked related questions before
> > > but I still have a problem.
> > >
> > >
> > > Usually, in the topology, OVS connected to hosts and they help hosts to
> > > communicate with each other. I prefer not to have any host and all nodes
> > in
> > > my network acts as forwarding elements (running OVS) (especially in case
> > of
> > > wireless networks, it is easier to add mobility to nodes without hosts).
> > >
> > > After having this topology (OVS1--OVS2---OVS3), with the following
> > > configuration:
> > >
> > > OVS1(eth0) ------- (eth0)OVS2
> > >
> > > ovs-vsctl add-br brx
> > > ovs-vsctl add-port brx ethx
> > > ip addr flush dev ethx
> > > ip addr add 10.0.0.x/16 dev brx
> > > ip link set brx up
> > >
> > >
> > > when 10.0.0.1 (br1) pings 10.0.0.2(br2), node1 sends a packet_in
> > > message(ICMP) to the controller(ONOS).
> > >
> > > But, when 10.0.0.1(br1) pings 10.0.0.3(br3), node1 sends a packet_in
> > > message(ARP) to the controller.
> > > While I do not except this ARP request to the controller. I am expecting
> > > ICMP message as a packet_in to the controller in the first place, after
> > > that based on the packet_out, node1 is supposed to send the ARP request
> > for
> > > the next hop. I do not know why OVS sends this ARP requests.
> > >
> > >  In this case, which part of the network needs to change? should I change
> > > the configuration of OVS and how?
> > >
> > > Thank you in advance
> > >
> > >
> > >
> > >
> > > On Tue, Apr 10, 2018 at 4:27 PM, Ben Pfaff <blp at ovn.org> wrote:
> > >
> > > > On Mon, Apr 09, 2018 at 01:09:37PM -0400, Sh j wrote:
> > > > > Hello,
> > > > >
> > > > > I have the following topology:
> > > > >
> > > > > host1 ----openvswitch1 ----openvswitch2----host2
> > > > >
> > > > > and both openvswitches are connected to the ONOS controller.
> > > > >
> > > > > The problem is that when host1 ping host2, openvswitch1 sends the ARP
> > > > > request as a packet_in to the controller, Also, it broadcasts the ARP
> > > > > request so that openvswitch2 receives this broadcast.
> > > > >
> > > > > Do you have any suggestion how to avoid this ARP broadcast?
> > > >
> > > > I would guess that ONOS can control this behavior through the flow
> > > > table.
> > > >
> >