Thanks Iwase and Carlos for your thoughts,

2 cases that this feature is interesting to me for would be:

Integrating Ryu with other software that is already running a different
webserver/asynchronous library. Nicer in this case not to have to deal with
2 different webservers/coroutine types.

Efficient failover if one Ryu application should fail for any reason, the
new one can instantly connect to the switch. Your suggestion to use the
ovsdb library could help with this one.

Thanks,
Matt

On Tue, Oct 3, 2017 at 7:20 PM, Iwase Yusuke <iwase.yusu...@gmail.com>
wrote:

> Hi Carlos,
>
> Thank you for your reply!
>
> As you said, the OpenFlow Spec does not restrict Switches must initiate
> connection to Controllers.
> But initiating connection by Controllers seems to be the "optional"
> feature.
> ===
> Quote: OpenFlow Spec 1.3.5 "6.3.3 Connection Setup"
> ===
> Optionally, the switch may allow the controller to initiate the
> connection. In this case, the switch should
> accept incoming standard TLS or TCP connections from the controller, using
> either a user-specified
> transport port or the default OpenFlow transport port 6653. Connections
> initiated by the switch and
> the controller behave the same once the transport connection is
> established.
> ===
>
> If OVS does not know on where Ryu is listening when OVS starting up, how
> about using OVSDB library
> to tell controller's IP:Port to OVS?
> If OVS listening on OVSDB connection, "set-controller" API can tell its
> own address to OVS.
>   https://github.com/osrg/ryu/blob/6e69e9b8a6ebd2bb06aa864cc76
> ef0b79d1ac9c3/ryu/lib/ovs/bridge.py#L128
>
> And apart from that, initiating connection by Controllers looks
> interesting feature for me.
>
> Thanks,
> Iwase
>
>
>
> On 2017年10月04日 08:57, Carlos Ferreira wrote:
>
>> This is just a question, not a critic.
>> Doesn't the OpenFlow standard stipulates that it is the Switch that
>> must connect to a Controller, and not the other way around?
>>
>> Carlos Ferreira
>>
>> On 4 October 2017 at 00:42, Iwase Yusuke <iwase.yusu...@gmail.com> wrote:
>>
>>>
>>> Hi Matt,
>>>
>>> As far as I know, Ryu does not provide such feature (only do wait
>>> incoming connection like server).
>>> Would you share us if you have any use-case or situation where Ryu must
>>> act as a client?
>>> If there are useful use-cases, better to implement it, I guess!
>>>
>>> Thanks,
>>> Iwase
>>>
>>>
>>>
>>> On 2017年10月04日 07:16, Matthew Moskowitz wrote:
>>>
>>>>
>>>> Hi,
>>>>
>>>> By default when a Ryu application is started, it is listening for a
>>>> connection request that comes from the switch. (For instance, using ovs,
>>>> you would run ovs-vsctl set-controller to tell it where to talk to the Ryu
>>>> application). However, OpenvSwitch can also behave like a server and wait
>>>> for a request from an openflow controller.
>>>>
>>>> Is there an existing setting that allows a Ryu application act as a
>>>> client such that the Ryu app will make the initial request to connect with
>>>> the openflow switch?
>>>>
>>>> Thanks,
>>>> Matt
>>>>
>>>>
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