[ovs-dev] [PATCH] OPENFLOW-1.1+: note on table-miss

[YAMAMOTO Takashi]

> On Tue, Oct 15, 2013 at 05:12:22PM +0900, YAMAMOTO Takashi wrote:
>> Signed-off-by: YAMAMOTO Takashi <yamamoto at valinux.co.jp>
>> ---
>>  OPENFLOW-1.1+ | 7 +++++++
>>  1 file changed, 7 insertions(+)
>> 
>> diff --git a/OPENFLOW-1.1+ b/OPENFLOW-1.1+
>> index 07b2660..4f30520 100644
>> --- a/OPENFLOW-1.1+
>> +++ b/OPENFLOW-1.1+
>> @@ -121,6 +121,13 @@ didn't compare the specs carefully yet.)
>>        [optional for OF1.3+]
>>  
>>      * More flexible table miss support.
>> +      This requires the following.
>> +      - Change the default table-miss action (in the absense of table-miss
>> +        entry) from packet_in to drop for OF1.3+.  Decide what to do if
>> +        a switch is configured to support multiple OF versions.
> 
> I'm wondering what is a good approach to take here.
> 
> It is possible to configure Open vSwitch (ovs-vswtichd) to only accept Open
> Flow 1.3+ connections.  In which case it should be possible to select the
> default behaviour described above.  However it is also possible for Open
> vSwitch (ovs-vswtichd) to be configured to accept a connections for Open
> Flow versions prior to 1.3, and 1.3+.
> 
> This is complicated by the fact that OpenFlow 1.3 conveniently deprecates
> all the TABLE_MOD bits that allow configuration of this behaviour. Though I
> assume deprecated doesn't mean not allowed.
> 
> With the constraints describe above and making the bold assumption that I'm
> not missing any further constraints I propose the following:
> 
> A:
>   1. If Open vSwtich is configured to only accept connections
>      for Open Flow 1.3+ then default to drop.
> 
>   2. Otherwise use the current default, packet_in.
> 
>   Is this a good idea? It may be to subtle to be useful in practice.

it sounds difficult to handle for controller-side programmers.

> 
> B:
>   Implement TABLE_MOD to allow it to be used to control the behaviour
>   of each table's miss behaviour.
> 
>   We could even go so far as to encourage people to use it,
>   even if they are using Open Flow 1.3+, to ensure that the
>   behaviour is what they expect.

this leaves the question what should be the default.

C:
    decide what to do (packet-in or drop) per ofconn basis,
    depending on OF versions.
    (ofconn_receives_async_msg can take care of this.)

    optionally, if a switch is configured to accept OF 1.3+ only,
    drop it in kernel as an optimization.

YAMAMOTO Takashi

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