[ovs-discuss] Need help on extending OVS to monitor/control network devices via SNMP

Giorgio Buffa buffagio+ml at gmail.com
Sat Jan 28 17:49:36 UTC 2012


Dear Ben,
Thanks for your interest to my problem.

Two pictures with the scenario and the role of OVS in this scenario are
attached. Following a brief explanation.

I would like to have a legacy network device (i.e. with no support to
OpenFlow) to be monitored and controlled by an OpenFlow Controller via the
OpenFlow Protocol.

Thus, the OpenFlow Protocol is to be translated to the management protocol
exposed by the network device (e.g., SNMP) by an adaptation layer, and vice
versa.

(There are some relevant limitation in this scenario, e.g. with the
handling of packet_out messages, or the production of packet_in messages,
but this is another story.)

I'd like to use OVS as the base for developing such adaptation layer, by
extending it with a module that would provide the OpenFlow-SNMP translation.

OVS already manages OpenFlow and provides a framework to handle with
different software/hardware platform, as described in the " How to Port
Open vSwitch to New Software or Hardware" document. Thus I'd leverage with
such framework and deploy my module as a dpif-provider / ofproto-provided
(I'm still not sure about which one to use).

Some of the use cases I'm evaluating are related to information retrieval
from device (e.g. get port statistics) or device configuration (e.g. the
forwarding table of a router -- next hop for a given destination). Truth to
be told, I'm still trying to figure out relevant usage stories.  :)

A long story short, THE PROBLEM IS how do I actually configure OVS to
load/use my module as the datapath to be managed?

I think I have to do something like:

 % ovs-vswitchd unix:/usr/local/var/run/openvswitch/db.sock --pidfile
--detach
% ovs-vsctl add-br my_test_bridge
 % ovs-vsctl set Bridge my_test_bridge datapath_type=snmp_adapter

# Use ovs-ofctl or OpenFlow controller to play with the network device via
the snmp_adapter

But I don't know how to register my module "snmp_adapter" with OVS and
whether I can use 'ovs-ofctl' to manage/debug it. Moreover I'm not sure
which part of the OVS codebase I have to modify, if any (e.g. the database
properties, …).

I was not able to find any relevant documentation on that. Can anyone
provide hits on the subject?

I hope that the explanation is more clear.
Kind regards,
Giorgio Buffa

On Sat, Jan 28, 2012 at 5:16 PM, Ben Pfaff <blp at nicira.com> wrote:

> On Sat, Jan 28, 2012 at 04:38:19PM +0100, Giorgio Buffa wrote:
> > I would like to use Open vSwitch for the monitoring/control of a legacy
> > data plane (i.e. with no support to OpenFlow). The idea is to extend OVS
> to
> > make it an adapter between the OpenFlow protocol (used by the control
> > plane) and SNMP (exposed by the underlying network devices). I'm
> evaluating
> > whether I can use OVS as the base for such adapter.
> >
> > I've studied the PORTING documentation, and relative interfaces
> > (lib/netdev-provider.h , lib/dpif-provider.h ,
> ofproto/ofproto-provider.h).
> > The problem is I cannot figure out how to deploy my own module (the one
> > which would provide the adaptation layer between OpenFlow and SNMP). In
> > other words, how do I configure OVS to load/use my module as the Openflow
> > datapath to be controlled?
>
> It's really unclear to me what exactly you want to do.  Could you
> implement what you want to do as an OpenFlow controller, or as an
> OpenFlow flow table, for example?  Can you give an example of what your
> module or your adaptation layer would do?
>
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