[ovs-discuss] How to use Click with OVS

Hamid Farhadi hamid.farhadi.nsc at gmail.com
Fri Oct 14 13:25:27 UTC 2011

Thank you very much Jesse,

any command you wanna see the output please?
My environment:
Ubuntu 10.10 2.6.35-30-generic inside a VMware Fusion. actually I am 
testing on this single machine. my route table is empty and I am doing 
everything on L2. I mean I do not use ARP/IP. I just set destination MAC 
directly on the packet using Click and send it over an interface. this 
is my simple click configuration file that starts the loop:

FromDevice(eth0) -> Queue -> ToDevice(tap1);

Also, one time I got the this message in dmesg: "/Dead loop on virtual 
device/ tap1, fix urgently"

this message is occurs when a virtual device's hard_start_xmit() 
function tries to transmit a packet using itself as output device.


On Fri Oct 14 09:39:41 2011, Jesse Gross wrote:
> On Thu, Oct 13, 2011 at 3:00 AM, Hamid Farhadi
> <hamid.farhadi.nsc at gmail.com> wrote:
>> Hi
>> I made a simple integration of Click router and OVS. when I receive a
>> packet, I modify it with Click then pass it to OVS via an Internal port
>> (Tap0) and then receive it from another port of OVS (i.e. Tap1) and 
>> modify
>> it again using Click and send it out of the box:
>> eth0 -> Click -> tap0 -> OVS -> tap1 -> Click -> eth0
>> both taps are internal ports made by OVS. once I send a packet to 
>> eth0, the
>> CPU goes up and system hangs down. I think there is a loop in system. 
>> as the
>> config, I have only two taps connected to br0. I am using click kernel
>> module.
>> any help pls?
> It does sound like you have a loop but it's pretty to debug without
> actually seeing the setup. OVS by itself has built-in loop prevention
> for traffic that stays on the box, so I'm guessing that the loop is
> being formed with something else on the network. A normal switch will
> have a self-forwarding check so it shouldn't form a loop by itself but
> maybe you have two of these things on the network?

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