[ovs-discuss] How to buffer on OVS

[Ben Pfaff]

OpenFlow 1.3 support is incomplete, as documented in the FAQ and
OPENFLOW-1.1+.  I did not look up whether this particular aspect of
OpenFlow 1.3 support is a matter of conformance, but it could be
improved.  Please consider contributing improvements.

On Fri, May 03, 2013 at 11:12:03AM +0900, Hiroshi Miyata wrote:
> Hi Ben,
> 
> In OpenFlow 1.3.1, the switch needs explict table-miss entry to be added,
> otherwise the packet which does not match any entry is discarded.
> The table-miss entry needs OFPAT_OUTPUT output action to OFPP_CONTROLLER.
> 
> -----------------------------
> OpenFlow1.3.1
> 5.4 Table-miss (last paragraph)
> If the table-miss flow entry does not exist, by default packets
> unmatched by flow entries are dropped
> (discarded). A switch configuration, for example using the OpenFlow
> Configuration Protocol, may
> override this default and specify another behaviour.
> -----------------------------
> 
> Therefore,
> 
> > In OVS, no packet_in message that results from an action ever
> allocates a buffer.
> 
> It seems to happen to Table-miss entry.
> 
> > Only a packet_in message that results from a flow table miss
> allocates a buffer.
> 
> If you supporse no action is specified to the table-miss entry, it
> does not seem to happen.
> 
> With above mentioned condition, OVS working in OpenFlow1.3.1 will
> not buffer the packet at all, correct?
> 
> 
> BTW.
> Regarding to the Reason code.
> 
> According to OpenFlow1.3.1
> A.4.1 Packet-In Message
> At the bottom of Page 92
> ----------------------------
> /* Why is this packet being sent to the controller? */
> enum ofp_packet_in_reason {
> OFPR_NO_MATCH = 0, /* No matching flow (table-miss flow entry). */
> OFPR_ACTION = 1, /* Action explicitly output to controller. */
> OFPR_INVALID_TTL = 2, /* Packet has invalid TTL */
> };
> ----------------------------
> 
> OFPR_NO_MATCH seems to be appropriate reason for table-miss entry
> even though it is the result of action.
> Otherwise, OFPR_NO_MATCH will not be used at all.
> 
> How do you think?
> 
> ...hiroshi miyata
> 
> (13/05/03 8:36), Ben Pfaff wrote:
> >On Fri, May 03, 2013 at 08:32:10AM +0900, Hiroshi Miyata wrote:
> >>Then, in what action requests to buffer?
> >>Sorry, I could not find appropriate part in the specification.
> >In OVS, no packet_in message that results from an action ever
> >allocates a buffer.  Only a packet_in message that results from a flow
> >table miss allocates a buffer.
>