[ovs-discuss] Open vSwitch question

Jesse Gross jesse at nicira.com
Thu Nov 11 03:22:53 UTC 2010

On Wed, Nov 10, 2010 at 5:28 PM, Nad Karim <nadk at yahoo.com> wrote:
> To whom it may concern:
> We are experimenting with Open vSwitch 1.1.0-pre2 with default settings and
> forwarding based on some flows.  We noticed that the mirroring function
> (SPAN) appears to be mutually exclusive with setting of a controller
> address.  Mirroring stops functioning when we add a controller to a bridge
> and restarts when we clear the controller entry from the bridge.  Is this by
> design?

OpenFlow has a "normal" action, which means to follow the typical
behavior of an L2 switch.  When Open vSwitch is not connected to a
controller all traffic is directed to this action by default.  Port
mirroring is part of the processing of the "normal" action.  If a
controller specifies a particular output port as the action then this
logic is bypassed and mirroring does not take place.  It would
probably be confusing to the controller writer to do so since traffic
would be directed to additional ports that they did not specify,
removing some of the control associated with OpenFlow.  In any case,
it is fairly easy to implement mirroring in the controller by
specifying additional output actions.  It is also possible for a
controller to directly use the "normal" action.

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