[ovs-discuss] Questions about IPFIX

Felix Konstantin Maurer felix.maurer at comsys.rwth-aachen.de
Wed Jun 21 12:21:02 UTC 2017


Hi Greg,

Just a small update. I tried to find the problem myself, and it seems to
me that there is only ever one packet received per sampling period.
In dpif_ipfix_bridge_sample there is:

2113 /* Use the sampling probability as an approximation of the number
2114  * of matched packets. */
2115 packet_delta_count = UINT32_MAX / di->bridge_exporter.probability;

which is why the IPFIX packet contains a number of packets greater than
one, even though only one is received by vswitch.

So my guess would be (I don't really know how openvswitch works) that
the kernel module only ever sends one packet per configured sampling period?

Regards
Felix

On 06/08/2017 10:32 PM, Greg Rose wrote:
> On 06/06/2017 05:18 AM, Felix Konstantin Maurer wrote:
>> I accidentally only responded to you, so here again what I wrote.
>> Thanks for the quick response! If tested it now but so far I see no
>> difference. All IPFIX packets have the same flowStartDelta and
>> flowEndDelta.
>>
>> Furthermore, about the first lines in ipfix_cache_aggregate_entries?
>>
>> line 1457
>>      to_start = &to_entry->flow_start_timestamp_usec;
>>      to_end = &to_entry->flow_end_timestamp_usec;
>>      from_start = &from_entry->flow_start_timestamp_usec;
>>      from_end = &from_entry->flow_end_timestamp_usec;
>>
>>      if (*to_start > *from_start) {
>>          *to_start = *from_start;
>>      }
>>      if (*to_end < *from_end) {
>>          *to_end = *from_end;
>>      }
>>
>> Is that not supposed to update the timestamps of the old entry, into
>> which the new stats are merged?
>>
>> Regards
>> Felix
>>
> 
> Felix,
> 
> I've been doing further testing on this and noticed that the code in the
> patch I
> submitted is never even being touched.
> 
> I'm debugging it but I am also working on some other bugs.  I'll work on
> this as I
> find time to do so.
> 
> Thanks,
> 
> - Greg

-- 
RWTH Aachen University
Communication and Distributed Systems
http://www.comsys.rwth-aachen.de

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