Re: [IPFIX] Export of long lived flow information

[Brian Trammell <[e-mail]>]

Hi, Gerhard, all,

Thought about this a bit too, and I can't come up anything better than the negative clarification. I might consider changing "preceding" and "succeeding" to "before" and "after" to simplify the language for non-native speakers, and stick an "observed" in there to make clear we're talking about observation time:

If this Information Element is present in a Flow Record, Flow properties in this Flow Record do not refer to packets observed before/after this timestamp.

It either case, it does make things a lot more explicitly clear, so I'd definitely add it to the timestamp/duration IEs.

Thanks, cheers,

Brian

On Oct 31, 2012, at 8:52 AM, Gerhard Muenz wrote:

> 
> Hi all,
> 
> I scanned through the IANA registry and briefly checked occurrences of "this Flow". I do not think that we need change them in general, except for those IEs which define a measurement interval.
> 
> So, we have:
> - flowStart* (including flowStartDeltaMicroseconds)
> - flowEnd* (including flowEndDeltaMicroseconds)
> - flowDuration*
> 
> My first shot was the following change for absolute flowStart*/flowEnd* timestamps:
> 
> OLD:
> The absolute timestamp of the first|last packet of this Flow.
> NEW:
> The absolute timestamp of the first|last packet accounted in this Flow Record.
> 
> We could add a sentence clarifying that the Flow properties reported in this Flow Record refer to the given measurement interval.
> At the moment, I only find a good "negative" way to describe this:
> "If this Information Element is present in a Flow Record, Flow properties in this Flow Record do not refer to packets preceding|succeeding this timestamp."
> 
> Do you have better suggestions?
> Or do you think that this clarification is not necessary?
> 
> Regards,
> Gerhard
> 
> 
> On 30.10.2012 13:38, Brian Trammell wrote:
>> Hi, Paul, all,
>> 
>> If someone throws together a quick summary of the position for me I'd
>> be happy make a couple of slides and do the presentation in person in
>> Atlanta.
>> 
>> From where I sit, it looks like we just go ask IANA to make the
>> registry change. Wearing my IE-Doctors-author hat (I can't wear an IE
>> Doctor hat, there aren't any yet. :) ), I'd say this revision would be
>> covered (and permissible) under point 2 in section 5.2 of ie-doctors.
>> 
>> Best regards,
>> 
>> Brian
>> 
>> 
>> On 30 Oct 2012, at 13:21 , Paul Aitken wrote:
>> 
>>> Gerhard,
>>> 
>>> I agree with your definitions. Thanks for clarifying.
>>> 
>>> So what's the next step?
>>> 
>>>   * Update the IANA definitions?
>>>   * Add clarifications to the WG documents?
>>> 
>>> 
>>> Do we need a short presentation at the upcoming WG meeting?
>>> 
>>> P.
>>> 
>>> 
>>> On 30/10/12 11:51, Gerhard Muenz wrote:
>>>> Paul,
>>>> 
>>>> On 26.10.2012 20:20, Paul Aitken wrote:
>>>>> Andrew, Gerhard,
>>>>> 
>>>>>>> My understanding is that both, deltaCounts and totalCounts contain the number of packets or octets observed in the indicated time interval. So, for identical flowStart* and flowEnd* timestamps, the values are the same.
>>>>>> This is my understanding as well.
>>>>> 
>>>>> There has to be a difference between delta and total counts, else we
>>>>> wouldn't have both of them!
>>>>> 
>>>>> Suppose we have a permanent cache, so the cache entries never expire.
>>>>> 
>>>>> For a new flow starting at t0 with a first export at t1, the
>>>>> timestamps, delta, and total counts are the same.
>>>>> 
>>>>> However with the second export at t2, the total and delta counts are
>>>>> different although their timestamps match (they'll both say, "t0 to
>>>>> t2").
>>>> 
>>>> No, this would contradict the new definition of flowStart* we are just discussing.
>>>> If delta counts are exported for the interval (t1,t2), then flowStart* is t1.
>>>> If delta counts are exported for the interval (t0,t2), then flowStart* is t0.
>>>> If total counts are exported, flowStart is always t0.
>>>> These statements hold regardless of which type of cache is used by the Metering Process. In general, the information model does not care about how the cache is implemented. The exported information just must follow the IE definition.
>>>> 
>>>>> 
>>>>> With the traditional (non-permanent) cache, the entry would probably
>>>>> have been removed at t1 and re-created on a subsequent packet, so at
>>>>> t2 the delta and total counts would both be equal. However it'd be
>>>>> incorrect to report the total count, because that's defined as the
>>>>> total number of packets or bytes ..."since the Metering Process
>>>>> (re-)initialization for this Observation Point".
>>>> 
>>>> You must not export total counters in this case because you reset counters before re-initialization of the Metering Process.
>>>> 
>>>> Thanks,
>>>> Gerhard
>>>> 
>>>>> 
>>>>> 
>>>>>>> However, the description of totalCounts says that you report the number of packets or octets observed for this Flow since re-initialization. So, you must never reset the counter for this Flow, even after observing a FIN or RST.
>>>>>>> If you reset flow counters, or if you remove Flows from your Cache, you cannot use totalCounts any more unless you re-initialize the Metering Process (e.g. after flushing the entire permanent Cache).
>>>>>> 
>>>>>> I can try some tests later, but from what I have seen (and been told) many totals being exported are in fact just a delta sent once at the end of the flow.  If a later flow had the same IPs, protocol, and ports as an earlier flow I'm pretty sure a new start time will be sent rather than the the first time that flow was seen since reinitializing the metering process.
>>>>> 
>>>>> So the MP uses a traditional (non-permanent) cache. In RFC 6728
>>>>> terms, a TimeoutCache or NaturalCache rather than a PermanentCache.
>>>>> 
>>>>> 
>>>>>> Or to put it an other way I think deltas are being sent, but called totals by the implementation because it seemed like the right thing to do for a value being sent once at the end of the flow.
>>>>> 
>>>>> The collector could be aggregating deltas to keep running totals.
>>>>> 
>>>>> 
>>>>>> I suspect that totals reporting on the export process (eg exportedOctetTotalCount, exportedMessageTotalCount) are, however, reported with a start time that is only reset on reinitialization.
>>>>> 
>>>>> Definitely, because these are defined as "The total number of X that
>>>>> the Exporting Process has sent since the Exporting Process
>>>>> (re-)initialization ...".
>>>>> 
>>>>> P.
>>> 
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