[ovs-discuss] packet reorderoing

Gray, Mark D mark.d.gray at intel.com
Wed Mar 4 16:53:45 UTC 2015


> From: Ben Pfaff [mailto:blp at nicira.com]
> Sent: Wednesday, March 4, 2015 4:51 PM
> On Wed, Mar 04, 2015 at 04:42:36PM +0000, Gray, Mark D wrote:
> > >
> > > On Wed, Feb 25, 2015 at 11:28:56AM -0600, swair shah wrote:
> > > > When packets which does not match any rule in ovs, are buffered at
> > > > the ingress switch, say first n packets are buffered. Switch sends
> > > > a flow_mod and message and packet_out for the buffered packets,
> > > > meanwhile if some more packets of the same flow arrive (say n+1 to
> > > > m), they'll also get buffered (as flow_mod) hasn't arrived yet.
> > > >
> > > > Once flow_mod message arrives at the switch then subsequent
> > > > packets of the flow will be forwarded but packets (n+1 to m) will
> > > > still be buffered waiting for their packet_outs. This results in
> > > > reordering of
> > > packets.
> > > >
> > > > Is there a way around this, besides from proactively setting up a flow?
> > > >
> > > > Is there a way to match flow_mod to existing buffered packets?
> > >
> > > Reordering can happen.  There isn't a way to avoid it entirely
> > > (besides proactive flow setup).  It isn't usually a problem, though,
> > > because most protocols only send one packet before they receive a
> > > reply from the opposite end.
> >
> > The only way that I can think to nail up a flow is via dpctl. Is this
> > how you suggest to do this?
> 
> Can you be more specific about what you want to do?  I can think of a few
> possibilities.

I don't know what Swair wants but I would like to be certain to avoid
reordering of packets traversing the vswitch. I suspect the way to do this
is to add a flow into the datapath and make it persistent so that upcalls
are never triggered.



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