Acked-by: Jarno Rajahalme <jrajaha...@nicira.com>
On Sep 11, 2013, at 10:02 AM, Ben Pfaff <b...@nicira.com> wrote:
> Reported-by: Aws Auger <ovshel...@gmail.com>
> Signed-off-by: Ben Pfaff <b...@nicira.com>
> ---
> FAQ | 50 ++++++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 50 insertions(+)
>
> diff --git a/FAQ b/FAQ
> index 7181484..20a3e3b 100644
> --- a/FAQ
> +++ b/FAQ
> @@ -1249,6 +1249,56 @@ A: An empty set of actions causes a packet to be
> dropped. You can
>
> ovs-ofctl add-flow br0 priority=65535,actions=drop
>
> +Q: I added a flow to send packets out the ingress port, like this:
> +
> + ovs-ofctl add-flow br0 in_port=2,actions=2
> +
> + but OVS drops the packets instead.
> +
> +A: Yes, OpenFlow requires a switch to ignore attempts to send a packet
> + out its ingress port. The rationale is that dropping these packets
> + makes it harder to loop the network. Sometimes this behavior can
> + even be convenient, e.g. it is often the desired behavior in a flow
> + that forwards a packet to several ports ("floods" the packet).
> +
> + Sometimes one really needs to send a packet out its ingress port.
> + In this case, output to OFPP_IN_PORT, which in ovs-ofctl syntax is
> + expressed as just "in_port", e.g.:
> +
> + ovs-ofctl add-flow br0 in_port=2,actions=in_port
> +
> + This also works in some circumstances where the flow doesn't match
> + on the input port. For example, if you know that your switch has
> + five ports numbered 2 through 6, then the following will send every
> + received packet out every port, even its ingress port:
> +
> + ovs-ofctl add-flow br0 actions=2,3,4,5,6,in_port
> +
> + or, equivalently:
> +
> + ovs-ofctl add-flow br0 actions=all,in_port
> +
> + Sometimes, in complicated flow tables with multiple levels of
> + "resubmit" actions, a flow needs to output to a particular port
> + that may or may not be the ingress port. It's difficult to take
> + advantage of OFPP_IN_PORT in this situation. To help, Open vSwitch
> + provides, as an OpenFlow extension, the ability to modify the
> + in_port field. Whatever value is currently in the in_port field is
> + the port to which outputs will be dropped, as well as the
> + destination for OFPP_IN_PORT. This means that the following will
> + reliably output to port 2 or to ports 2 through 6, respectively:
> +
> + ovs-ofctl add-flow br0 in_port=2,actions=load:0->NXM_OF_IN_PORT[],2
> + ovs-ofctl add-flow br0 actions=load:0->NXM_OF_IN_PORT[],2,3,4,5,6
> +
> + If the input port is important, then one may save and restore it on
> + the stack:
> +
> + ovs-ofctl add-flow br0 actions=push:NXM_OF_IN_PORT[],\
> + load:0->NXM_OF_IN_PORT[],\
> + 2,3,4,5,6,\
> + pop:NXM_OF_IN_PORT[]
> +
>
> Contact
> -------
> --
> 1.7.10.4
>
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