[ovs-discuss] a problem about passing metadata in packet-in

Ben Pfaff blp at ovn.org
Sat Nov 14 19:15:23 UTC 2015


Yes, I agree that write_metadata is limited; it's defined by OpenFlow
that way so we can't easily change it.  Using "load" is a better
approach.

On Fri, Nov 13, 2015 at 01:46:37AM +0000, Chao Hu wrote:
> Hi Ben,
> 
> Thanks for your reply!
> Seems the action "write_metadata" is not allowed to set before "Controller", so I tried to use " load:****->NXM_NX_REG*" instead, to pass any data to controller and it worked.
> I think the usage of metadata is very limited if so. 
> Pls correct me.
> 
> Thanks
> Chao
> 
> -----Original Message-----
> From: Ben Pfaff [mailto:blp at nicira.com] 
> Sent: Tuesday, August 25, 2015 1:37 AM
> To: Chao Hu
> Cc: discuss at openvswitch.org
> Subject: Re: [ovs-discuss] a problem about passing metadata in packet-in
> 
> On Fri, Aug 21, 2015 at 07:51:15PM +0000, Chao Hu wrote:
> > I'm trying to pass metadata from OVS switch to controller but always get 0. Anything wrong with my steps?
> > My test environment is:
> > OVS: 2.0.2
> > OVS-controller: 2.3.1
> > OF: OpenFlow1.3
> > 
> > My test steps are:
> > 
> > 1.  Make OVS-controller to send a OFPRAW_NXT_SET_PACKET_IN_FORMAT 
> > message to OVS switch, to set the packet-in-format to NXM (Nicira 
> > Extended). As I captured, it's a OFPT_EXPERIMENTER packet and the 
> > content is exactly the same with the packet of running "ovs-ofctl 
> > monitor -P nxm tcp:myip:6653 -O OpenFlow13". Seems Switch do nothing 
> > after received this packet.
> 
> This is a bad idea.  The OpenFlow 1.3 packet-in format is already extensible so there should be no need to change it.
> 
> > 2.        Add a flow to OVS switch:
> > cookie=0x0, duration=28.019s, table=0, n_packets=0, n_bytes=0, 
> > in_port=2 actions=CONTROLLER:65535,write_metadata:0x11/0xffff
> > 
> > 3.       OVS switch send the packet-in traffic to controller when it matches above flow, but metadata is 0.
> 
> The actions above set the metadata after sending the packet to the controller.



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