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

张伟 zhangwqh at 126.com
Sat Nov 22 02:10:23 UTC 2014

Can you give some advice what is the difference between tap device and internal device? 

From man and some examples, I know the meaning of fields, basis, algorithm multipath(fields, basis, algorithm, n_links, arg, dst[start..end]), n_links. However I do not know how I should give the dst[start..end]. What is the relation between n_links and dst[start..end]? n_links means that if I have 4 ports using multipath, it should be 4, right? I have a confused a question. Where can I  define, which ports I want to use it as the multipath ports group?   How the system can know which ports I want to use and give the result?

At 2014-11-22 06:50:31, "Ben Pfaff" <blp at nicira.com> wrote:
>On Fri, Nov 21, 2014 at 10:28:02AM +0800, ???? wrote:
>> 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.
>Internal devices are not tap devices, unless you are using the
>userspace switch (datapath_type=netdev), so they do not behave


>> 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.
>What information do you want?  It sounds like you have already read
>the documentation.
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