[ovs-discuss] Set up OpenFlow using OpenvSwitch

Jesse Gross jesse at nicira.com
Thu Nov 11 03:12:17 UTC 2010

2010/11/9 Yue ZHANG <cassidy.zy at gmail.com>:
> Hi, dear,
> Thanks for your quickly reply.
> I've insmod the OvS to replace original kernal bridge in the KVM host, and
> configured br0 and vif1(qemu param:-net tap,vlan=0,ifname=vif1) which is the
> interface of the KVM guest.
> #ovs-vsctl add-br br0
> #ovs-vsctl add-port br0 vif1
> Then it seems like that:
> #ovs-dpctl show br0
> system at dp0:
>  flows: xxxx
>         ...
>         port 0: br0 (internal)
>         port 1: vif1               <--- The KVM guest interface
> Then I ifconfig br0 with in the KVM host, and ifconfig eth0 with
> in the KVM guest.
> I think the KVM guest( and br0( should be connected
> automatically, is it? But the tcpdump result is strange that the vif1 could
> send packet to br0, but could not receive any incoming packet.
> If ping from kvm guest(2.2) to br0(2.1), br0 will receive arp request and
> return mac addr correctly, but the guest(2.2) will not receive the returned
> mac addr.
> If ping from br0 to kvm guest, br0 sent arp request, but kvm guest(2.2)
> still received no packet.
> There maybe something wrong, either the configuration of OvS or the KVM, it
> will be great help if you have some ideas, or give me some suggestions on
> how to debug, thanks!

Hmm, normally traffic should be able to flow in both directions,
assuming a default configuration.  Are you using an OpenFlow

Assuming not, there are a few things that I would look at:
ovs-ofctl dump-flows br0 (this will give the high level OpenFlow flows)
ovs-dpctl dump-flows br0 (this will show how the OpenFlow flows are
applied to the current traffic)
tcpdump on the various interfaces: br0, vif1, eth0 in the guest to see
where traffic is getting dropped or if it is making it through but the
OS is not responding

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