[ovs-dev] switch local port

Gaetano Catalli gaetano.catalli at gmail.com
Wed Feb 23 15:30:12 UTC 2011


On Fri, Feb 11, 2011 at 6:09 PM, Ben Pfaff <blp at nicira.com> wrote:
> On Fri, Feb 11, 2011 at 06:05:08PM +0100, Gaetano Catalli wrote:
>> I have some doubts to resolve about switch local port.
>> Firstly, in the ovs-openflowd manpage I can read: "...The Open???Flow
>> local port is a virtual network port that ovs-openflowd bridges to the
>> physical switch ports...". I'm searching through the sources but I
>> can't find out where this bridging operation is realised. Can you
>> kindly show it to me? I'm working on the 1.1.0pre2 code version.
>
> vswitchd/bridge.c
>
>> Moreover, I don't understand which exactly is the role played by this
>> virtual device and in which cases it is used. Can you explain me it?
>
> If you want to configure an IP address for the bridge, you put that IP
> address on the local port.  (This is the same role as with the Linux
> bridge.)

Why a tap device is used as local port?

Then I can't understand well the comment in 'netdev_linux_open()' :
"We can assume that the first user of the tap device is the primary
user and give them the tap FD. Subsequent users probably just expect
this to be a system device so open it normally to avoid send/receive
directions appearing to be reversed."

Why the send/receive directions could appear reversed?
Why this tap device could be opened more than one time?

Thanks.
-- 
gaetano catalli




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