[ovs-discuss] sFlow

Neil McKee neil.mckee at inmon.com
Fri Sep 4 23:02:46 UTC 2009


Justin,

Please accept this email as written confirmation that you may use and  
adapt the source code for the InMon Virtual Probe (http://inmon.com/ 
products/virtual-probe/index.php) for the implementation of an sFlow  
agent in the "Open vSwitch" project (http://openvswitch.org/) under  
the terms of the sFlow License (http://www.sflow.org/developers/ 
licensing.php).

Neil McKee
Director
InMon Corp.


On Aug 28, 2009, at 10:38 PM, Neil Mckee wrote:

> The sFlow SNMP MIB,  while very useful,  is optional.  It can be  
> ignored for now.
>
> The only counter-block you really need is the "generic" one,  which  
> exports the basic MIB-II ifTable counters as a single snapshot.  I  
> can see that this might be awkward because these counters must be  
> updated with every packet,  in the fast-path.   Still,  you'll  
> probably be expected to provide them eventually one way or another.
>
> The simplest sampling implementation is usually to have just one  
> packet-sampler for the whole switch,  and the critical path there  
> is just to decrement the countdown to the next sample,  so that  
> part is not going to slow you down at all.  I guess it's just a  
> question of figuring out the best way to queue the samples for  
> processing in user-space.
>
> There are patents involved,  yes,  but the main sFlow license  
> should not be an obstacle (http://www.sflow.org/developers/ 
> licensing.php).   The license you were looking at was specific to  
> the virtual probe implementation.    I'll check what we need to do  
> to,  but it looks like it's probably enough for me to say in  
> writing that you are welcome to use that code as long as you  
> conform to the main sFlow license.  You'll probably rewrite the  
> code anyway :).  Our main goal in putting it out there was just to  
> say "wow, look how easy this is".
>
> regards,
> Neil
>
>
> On Aug 28, 2009, at 6:23 PM, Justin Pettit wrote:
>
>> Hi, Neil.  Thanks for the information!  We'd like to add native  
>> support, but there are a few things that would need to be done:
>>
>> 	- sFlow uses SNMP to communicate between the collector and  
>> agents, and we do not yet have support for SNMP.
>>
>> 	- For packet sampling, we'd need to make some modifications to  
>> the protocol used to communicate with the datapath (in addition to  
>> changes in the kernel and userspace).
>>
>> 	- For counter sampling, we'd need to keep track of a lot more  
>> information than we currently do.
>>
>> Luckily, none of these technical issues are hard.  Our biggest  
>> concern has been related to licensing and patents, since this is  
>> an open source project.  Does InMon claim any patents or licensing  
>> restrictions over projects that implement RFC 3176?
>>
>> The Virtual Switch Probe looks like a neat program and should work  
>> with the current version of Open vSwitch.  However, clause 1(b) in  
>> the license agreement that prevents using it for any commercial  
>> purposes seems a bit worrying.
>>
>> --Justin
>>
>>
>> On Aug 28, 2009, at 5:17 PM, Neil McKee wrote:
>>
>>> Hello all,
>>>
>>> I saw you had sFlow on your list of features that are "under  
>>> development",  so I thought I would offer to help if I can.   If  
>>> you're just getting started, the source code linked from this  
>>> page might help:
>>>
>>> http://inmon.com/products/virtual-probe/index.php
>>>
>>> (It the C source code to an sFlow agent designed to connect to a  
>>> virtual SPAN port using libpcap).
>>>
>>> If you already have something running,  then I'd be happy to help  
>>> with the testing.
>>>
>>> Neil McKee
>>> InMon Corp.
>>>
>>>
>>> _______________________________________________
>>> discuss mailing list
>>> discuss at openvswitch.org
>>> http://openvswitch.org/mailman/listinfo/discuss_openvswitch.org
>





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