[ovs-discuss] tunctl tap device attached to openvswitch bridge, why the type changed to system interface

张伟 zhangwqh at 126.com
Fri Nov 21 02:28:02 UTC 2014

I want to clear my problem I met. 

I have two physical machines A and B. Each machine I want to create a tap device and vxlan device, configure the flow entries according my requirement. I want to successfully ping the tap device on  machine B from  the tap device on machine A. 

However, if I use tunctl -t tap0 to create the tap device and then attach to the openvswitch. When I check the tap device type, it is empty. From the man, the empty means system type. Usually the physical eth has the system type. When I use ovs-vsctl add-port bridge-name device-name -- set Interface device-name type=internal to create the device and attach, it works. From google, internal type actually is the tap device. This is my confused question: why I directly use tunctl to create the tap device and attach to the bridge, my tap device will directly drop the packets. 

I have another question:
I want to configure the multipath feature using ovs-ofctl add-flow command line. However, I do not clearly know how to do that. Can you give me some advice? Where I can check and find how to use it? I have checked the man ovs-ofctl and man 5 ovs-vswitchd.conf.db and did not find useful information. 

At 2014-11-21 00:41:16, "Ben Pfaff" <blp at nicira.com> wrote:
>On Thu, Nov 20, 2014 at 03:58:18PM +0800, zhangwqh wrote:
>> I met a problem. I want to firstly create a tap device. I used the
>> tool tunctl to create the tap device, After that, I attached the
>> interface to openvswitch bridge. When check the type, the type is
>> empty string. 
>That's fine and expected.
>> From the man 5 ovs-vswitchd.conf.db,
>>  type: string
>>               The interface type, one of:
>>               system An  ordinary  network  device,  e.g.  eth0  on Linux.  Sometimes referred to as ''external interfaces'' since they are generally connected to hardware
>>                      external to that on which the Open vSwitch is running.  The empty string is a synonym for system.
>Note the final sentence above.
>>  it seems that after attaching to bridge, the type is system
>>  type. Usually the physical ethernet port is system type. When I want
>>  to send the packets to vxlan device from the tap device I created
>>  using tunctl(I have set a flow entry from tap device to vxlan
>>  device), I found that the tap device dropped all of the packets. Can
>>  anybody give me some advices why this happens?
>I don't know, because I don't have enough information, but the interface
>type is not what you should focus on.
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