Re: [IPFIX] RFC5101: time first flow dropped and time last flow dropped

[Benoit Claise <[e-mail]>]

Brian,
> Hi, Paul, all,
>
> I suppose I should state for the sake of completeness that this is the first I've ever actually _thought_ about the MPRSO. I find the whole use case for it rather dubious -- it presumes an MP with somehow trustworthy knowledge about packet loss, which is never the case,
Well, I can give you an example of Cisco devices, with metering in 
hardware, that displays the number of packets that were not taken into 
account, due to excessive cache collisions.

Regards, Benoit.
>   and relying on such information at the collector side for anything other than entertainment purposes is fraught with peril -- so I saw the MAY on section 4 in 5101, was thankful it wasn't a MUST I had to fight against and/or simply ignore, and never looked back.
>
> That said, it does make sense to fix, since it's there.
>
> On Sep 27, 2011, at 10:25 PM, Paul Aitken wrote:
>
>> How do you know that the received template is a MPRSO?
> Does it matter? Seriously, what is the difference between "an MPRSO" and "a template containing information about lost packets for a given time interval, along with maybe some other information"? Do we actually want to require an MP to keep time interval information for loss? Wouldn't those resources be better deployed not losing packets in the first place? So let's say I want to report missing packets, but don't have information about when I lost them. Do I have to throw a timestamp in there anyway in order for it to be "an MPRSO"?
>
> I think these are arguments against having the timestamps at all (or to include them, with a further instruction that they are optional).
>
>>     - must the fields be exactly in the specified order and no other combination in order to be a valid MPRSO?
> This isn't a valid template recognition strategy in IPFIX. At least, it hasn't been to date, and it's a bad idea to make it so. IE-Doctors contains language meant to instruct IPFIX application authors to refrain from specifying such magic templates.
>
>>     - how do you know which of the observationTime* elements (or missingObservationWindowEdge elements) is the first and which is the last?
>>         - only from their position in the template (so, field order and position are crucial)
>>         - by comparing them (so field order and position aren't important)
> Time intervals can be treated as a special case, here, since time can generally be assumed to go in only one direction. "The time interval from A to B" is completely equivalent to "the time interval from B to A", so one could argue order doesn't matter. (We don't argue that anywhere in IPFIX, to be true. But what do I do when I get a flow with an endTime before the startTime?)
>
>> Suppose a mediator adds, removes, or re-orders the fields.
>>     - does this invalidate the MPRSO?
>>     - how does a mediator know not to do this?
>>     - how does the collector cope if a mediator does?
> These questions seem to apply only to the case where MPRSO is magical. I'm trying to define it such that it isn't.
>
>> The change to "missingObservationWindowEdge" is simply a rename of observationTime. I don't see that it adds anything.
> observationTime already has a meaning. "This Information Element specifies the absolute time in seconds of an observation." In other words, "I saw the thing I'm talking about in this record at the specified time". It has never to date been specified in such a way that it means "I saw the thing I'm talking about in this record at the specified time, unless the record contains two observationTimes, in which case I saw the thing in the time interval between those two things".
>
> missingObservationWindowEdge means "there is missing information within an interval described between this IE and the other identical IE in the record". If we keep the MPRSO defined as it is (and fix it only by dropping in , missingObservationWindowStartSeconds and missingObservationWindowEndSeconds, since it's more IPFIXish, but there was concern voiced in this thread about IE space explosion, so I figured we could exploit the nature of time and cut down on the IEs required by half.
>
> The advantage of a new IE is that it isn't overloaded, but more importantly that it does not lead to an ambiguous interpretation of the entire template at the collector.
>
>> A long basicList isn't the right solution because
>>     - various list lengths mean there are multiple possible templates making the detection of the MPRSO a little more difficult
>>        ie, it's no longer a fixed template, nor a combination of a few possibilities, but a great many different possible templates.
>>     - there are two different semantics for the start and end of the window, so it's actually an ordered list of pairs ie a subTemplateList.
>> Lists can have zero elements. However, if you want to report that nothing was lost, the ignored*Count = 0 report should indicate the start and end of the 100% period. A list length of zero doesn't tell when stuff was or was not lost - so it's of limited usefulness, unless perhaps as a total figure? Again, see questions above about what is / is not a valid MPRSO.
> I withdraw my basicList comment; it was essentially just "thinking aloud", and I didn't actually intend to include a mention of it in the 5101bis MPRSO. 1. It doesn't really add anything to the original intent of the MPRSO, and 2. adding it in 5101bis would cause 5101bis to have a normative dependency on 6313, which is a terrible idea.
>
> Cheers,
>
> Brian
>
>> On 27/09/11 18:30, Andrew Feren wrote:
>>> Hi Brian,
>>>
>>> Well stated.
>>>
>>> Additional comments inline
>>>
>>> On 09/27/2011 12:15 PM, Brian Trammell wrote:
>>>> Greetings, all,
>>>>
>>>> This is a little bit of an abuse of the ordering of IEs, in my opinion, and of the general rule that only IEs, and the scope in which they are defined, carry semantics. Even for templates which are defined within Standards Track RFCs, the records defined by the template should be decipherable without reference to the RFC. Put another way, we should not define magical templates, and this template as proposed looks pretty magical.
>>> Yes, a black magic sort of magical.  We have been discussing this proposed change in the office and coming to the same conclusion.
>>>> Without reading the text of this thread, and following basically everything we've ever said about multiple IEs in a record, I would interpret a record matching this template as follows:
>>>>
>>>> For the metering process A and observation domain B:
>>>> N packets were ignored; these contained a total of M octets.
>>>> The first observation at this metering process was at time T0.
>>>> The second observation at this metering process was at time T1.
>>> This was exactly how I interpreted this template until I read the updated draft and saw the bit about "the Collecting Process MUST determine which is the oldest and the most recent timestamp in order the determine the right semantic ...."
>>>
>>>> This is quite far from the stated intention. I would strongly suggest that we not so lightly give up on "templates should be unambiguously understandable" requirement, even if the exception itself lives in the core protocol document.
>>>>
>>>> I would suggest, if you want to do a multiple IE solution here, you define something like missingObservationWindowEdge, and have two of them:
>>>>
>>>>    observationDomainId {scope}
>>>>    meteringProcessId {scope}
>>>>    ignoredPacketTotalCount
>>>>    ignoredOctetTotalCount
>>>>    missingObservationWindowEdge
>>>>    missingObservationWindowEdge
>>>>
>>>> This has the advantage that you can have a long basicList of window edges in order to define multiple missing observation windows; each edge pair is a loss window.
>>> I like this suggestion, and I have a few additional thoughts.
>>>
>>> Perhaps the basic list of edge times should either be limited to only one pair or the ignored*TotalCount IEs needs to be in a basiclist with N entries too.
>>>
>>> How about observationWindowEdge instead (no "missing") to be more generally useful.
>>>
>>> I think a list of time edges also works neatly when sending this template at regular intervals (which SHOULD be done).  When the ignored*TotalCount IEs are zero, an empty list makes sense for edge times.
>>>
>>>
>>>> Seconds suffice for these, I think. You might want to do one in milliseconds. But if you have the resources to calculate your packet loss window to nanosecond precision without having the resources to not lose packets, I humbly submit you've picked the wrong engineering tradeoffs. :)
>>> Unless window edge isn't defined specifically for "missing" values.  Then the higher precision timestamps might have some use.
>>>
>>> -Andrew
>>>> Best regards,
>>>>
>>>> Brian
>>>>
>>>> On Sep 23, 2011, at 11:07 PM, Andrew Feren wrote:
>>>>
>>>>> Yes, this makes sense.
>>>>>
>>>>> I gave this some thought and I don't have a better suggestion.  I also agree that even though the flow[Start|End]* collection of IEs conveniently has one IE for both first and last, observationTime* is the more correct choice here.
>>>>>
>>>>> -Andrew
>>>>>
>>>>> On 09/22/2011 03:54 AM, Benoit Claise wrote:
>>>>>> Hi Andrew,
>>>>>>> Hi Benoit,
>>>>>>>
>>>>>>> I had the same thought about using
>>>>>>>
>>>>>>> 322    observationTimeSeconds
>>>>>>> 323    observationTimeMilliseconds
>>>>>>> 324    observationTimeMicroseconds
>>>>>>> 325    observationTimeNanoseconds
>>>>>>>
>>>>>>> The problem is that you need two timestamps in the same record (first and last).  How does that work with the above?
>>>>>> Excellent question. We debated this question with Paul Aitken recently.
>>>>>> Let me rephrase the question slightly differently: how does the collector determine that this is a "The Metering Process Reliability Statistics Options Template", and understands the semantic of the two counters?
>>>>>> Well. Two solutions:
>>>>>> 1. we duplicate all the IEs to have the exact correct semantic.
>>>>>>      ObservationTime[packet|flow][first|last][Seconds|Milliseconds|Microseconds|Nanoseconds] ... and potentially some more such as pre|post
>>>>>>      This brings multiple new dimensions to IE and will lead to an explosion of IEs if we want to cover all the case
>>>>>> 2. the collector tests the possible combination of IE in the Options Template Record.
>>>>>>      For example, if the collector sees such an Options Template Record, it knows that this a "The Metering Process Reliability Statistics Options Template"
>>>>>>    observationDomainId (scope)
>>>>>>    meteringProcessId (scope)
>>>>>>
>>>>>>    ignoredPacketTotalCount
>>>>>>    ignoredOctetTotalCount
>>>>>>    observationTimeSeconds | observationTimeMilliseconds | observationTimeMicroseconds | observationTimeNanoseconds
>>>>>>    observationTimeSeconds | observationTimeMilliseconds | observationTimeMicroseconds | observationTimeNanoseconds
>>>>>>
>>>>>>
>>>>>> While the solution 2 is not perfect, this was the chosen track.
>>>>>>
>>>>>> Does it make sense?
>>>>>>
>>>>>> Regards, Benoit
>>>>>>> -Andrew
>>>>>>>
>>>>>>> On 09/21/2011 07:11 PM, Benoit Claise wrote:
>>>>>>>> Hi Gerhard,
>>>>>>>>
>>>>>>>> Thanks for your reply.
>>>>>>>> See in line.
>>>>>>>>> Hi Benoit,
>>>>>>>>>
>>>>>>>>> See comments inline.
>>>>>>>>>
>>>>>>>>> On 20.09.2011 16:19, Benoit Claise wrote:
>>>>>>>>>> Dear all,
>>>>>>>>>>
>>>>>>>>>> [this email addresses draft-claise-ipfix-protocol-rfc5101bis-00.txt,  TO DO ->   "time first flow dropped" and "time last flow dropped" inconsistency.  See the discussion on the list.]
>>>>>>>>>>
>>>>>>>>>> Paul Aitken discovered this issue.,
>>>>>>>>>>
>>>>>>>>>>  From [RFC5101], section 4.3. The Exporting Process Reliability Statistics Option Template
>>>>>>>>>>
>>>>>>>>>> time first flow dropped
>>>>>>>>>>                          The timestamp of the first Flow was dropped by
>>>>>>>>>>                          the Metering Process.  For this timestamp, any
>>>>>>>>>>                          of the "flowStart" timestamp Information
>>>>>>>>>>                          Elements flowStartMilliseconds,
>>>>>>>>>>                          flowStartMicroseconds, flowStartNanoseconds, and
>>>>>>>>>>                          flowStartDeltaMicroseconds can be used.
>>>>>>>>>>
>>>>>>>>>> time last flow dropped
>>>>>>>>>>                          The timestamp of the last IP packet that was
>>>>>>>>>>                          ignored by the Metering Process.  For this
>>>>>>>>>>                          timestamp, any of the "flowEnd" timestamp
>>>>>>>>>>                          Information Elements flowEndMilliseconds,
>>>>>>>>>>                          flowEndMicroseconds, flowEndNanoseconds, and
>>>>>>>>>>                          flowEndDeltaMicroseconds can be used.
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> Firstly, these definitions are inconsistent since the names and the first definition say "flow" while the second definition says "IP packet". Obviously "IP packet" != "flow" :-o
>>>>>>>>>>
>>>>>>>>>> Secondly, "The timestamp of the first Flow was dropped by the Metering Process." is bad English: at least it's missing "that".
>>>>>>>>>>
>>>>>>>>>> Thirdly, the section 4.2 doesn't take into account a metering process id. Indeed, what if we have multiple caches on the exporter?
>>>>>>>>>>
>>>>>>>>>> Here is a proposal for 4.2 and 4.3. The underlined parts are new
>>>>>>>>>>
>>>>>>>>>> 4.2.  The Metering Process Reliability Statistics Option Template
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>     The Metering Process Reliability Option Template specifies the
>>>>>>>>>>     structure of a Data Record for reporting lack of reliability in the
>>>>>>>>>>     Metering Process.  It SHOULD contain the following Information
>>>>>>>>>>     Elements that are defined in [
>>>>>>>>>> RFC5102
>>>>>>>>>> ]:
>>>>>>>>>>
>>>>>>>>>>     observationDomainId
>>>>>>>>>>                             An identifier of an Observation Domain that
>>>>>>>>>>                             is locally unique to the Exporting Process.
>>>>>>>>>>                             This Information Element MUST be defined as a
>>>>>>>>>>                             Scope Field.
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>     meteringProcessId (*)
>>>>>>>>>>                             The identifier of the Metering Process for
>>>>>>>>>>                             which lack of reliability is reported.  There
>>>>>>>>>>                             This Information Element MUST be defined as a
>>>>>>>>>>                             Scope Field.
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>     ignoredPacketTotalCount
>>>>>>>>>>                             The total number of IP packets that the
>>>>>>>>>>                             Metering Process did not process.
>>>>>>>>>>
>>>>>>>>>>     ignoredOctetTotalCount
>>>>>>>>>>                             The total number of octets in observed IP
>>>>>>>>>>                             packets that the Metering Process did not
>>>>>>>>>>                             process.
>>>>>>>>>>
>>>>>>>>>>     time first
>>>>>>>>>> packet
>>>>>>>>>> ignored
>>>>>>>>>>                             The timestamp of the first IP packet that was
>>>>>>>>>>                             ignored by the Metering Process.  For this
>>>>>>>>>>                             timestamp, any of the "flowStart" timestamp
>>>>>>>>>>                             Information Elements flowStartMilliseconds,
>>>>>>>>>>                             flowStartMicroseconds, flowStartNanoseconds,
>>>>>>>>>>                             and flowStartDeltaMicroseconds can be used.
>>>>>>>>>>
>>>>>>>>>>     time last
>>>>>>>>>> packet
>>>>>>>>>> ignored
>>>>>>>>>>                             The timestamp of the last IP packet that was
>>>>>>>>>>                             ignored by the Metering Process.  For this
>>>>>>>>>>                             timestamp, any of the "flowEnd" timestamp
>>>>>>>>>>                             Information Elements flowEndMilliseconds,
>>>>>>>>>>                             flowEndMicroseconds, flowEndNanoseconds, and
>>>>>>>>>>                             flowEndDeltaMicroseconds can be used.
>>>>>>>>>>
>>>>>>>>> I do not find these IEs in RFC5102.
>>>>>>>> Which ones?  flowEndMilliseconds, flowEndMicroseconds, flowEndNanoseconds, and flowEndDeltaMicroseconds
>>>>>>>> There are in http://www.iana.org/assignments/ipfix/ipfix.xml
>>>>>>>> However, re-reading
>>>>>>>>     time first packet
>>>>>>>> ignored
>>>>>>>>                             The timestamp of the first IP packet that was
>>>>>>>>                             ignored by the Metering Process.  For this
>>>>>>>>                             timestamp, any of the "flowStart" timestamp
>>>>>>>>                             Information Elements flowStartMilliseconds,
>>>>>>>>                             flowStartMicroseconds, flowStartNanoseconds,
>>>>>>>>                             and flowStartDeltaMicroseconds can be used.
>>>>>>>>
>>>>>>>>     time last
>>>>>>>> packet
>>>>>>>> ignored
>>>>>>>>                             The timestamp of the last IP packet that was
>>>>>>>>                             ignored by the Metering Process.  For this
>>>>>>>>                             timestamp, any of the "flowEnd" timestamp
>>>>>>>>                             Information Elements flowEndMilliseconds,
>>>>>>>>                             flowEndMicroseconds, flowEndNanoseconds, and
>>>>>>>>                             flowEndDeltaMicroseconds can be used.
>>>>>>>>
>>>>>>>> And http://www.iana.org/assignments/ipfix/ipfix.xml for the "flowEnd" timestamp IE,
>>>>>>>> I now believe that we should be using this series of IEs
>>>>>>>> 322    observationTimeSeconds
>>>>>>>> 323    observationTimeMilliseconds
>>>>>>>> 324    observationTimeMicroseconds
>>>>>>>> 325    observationTimeNanoseconds
>>>>>>>>
>>>>>>>>>> 4.3.  The Exporting Process Reliability Statistics Option Template
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>     The Exporting Process Reliability Option Template specifies the
>>>>>>>>>>     structure of a Data Record for reporting lack of reliability in the
>>>>>>>>>>     Exporting process.  It SHOULD contain the following Information
>>>>>>>>>>     Elements that are defined in [
>>>>>>>>>> RFC5102
>>>>>>>>>> ]:
>>>>>>>>>>
>>>>>>>>>>     Exporting Process ID
>>>>>>>>>>                          The identifier of the Exporting Process for
>>>>>>>>>>                          which lack of reliability is reported.  There
>>>>>>>>>>                          are three Information Elements specified in
>>>>>>>>>>                          [
>>>>>>>>>> RFC5102
>>>>>>>>>> ] that can be used for this purpose:
>>>>>>>>>>                          exporterIPv4Address, exporterIPv6Address, or
>>>>>>>>>>                          exportingProcessId.  This Information Element
>>>>>>>>>>                          MUST be defined as a Scope Field.
>>>>>>>>>>
>>>>>>>>>>     notSentFlowTotalCount
>>>>>>>>>>                          The total number of Flows that were generated by
>>>>>>>>>>                          the Metering Process and dropped by the Metering
>>>>>>>>>>                          Process or by the Exporting Process instead of
>>>>>>>>>>                          being sent to the Collecting Process.
>>>>>>>>>>
>>>>>>>>>>     notSentPacketTotalCount
>>>>>>>>>>                          The total number of packets in Flow Records that
>>>>>>>>>>                          were generated by the Metering Process and
>>>>>>>>>>                          dropped by the Metering Process or by the
>>>>>>>>>>                          Exporting Process instead of being sent to the
>>>>>>>>>>                          Collecting Process.
>>>>>>>>>>
>>>>>>>>>>     notSentOctetTotalCount
>>>>>>>>>>                          The total number of octets in packets in Flow
>>>>>>>>>>                          Records that were generated by the Metering
>>>>>>>>>>                          Process and dropped by the Metering Process or
>>>>>>>>>>                          by the Exporting Process instead of being sent
>>>>>>>>>>                          to the Collecting Process.
>>>>>>>>>>
>>>>>>>>>>     time first flow dropped
>>>>>>>>>>
>>>>>>>>>>                        The time at which the first Flow Record was dropped by
>>>>>>>>>>                          the
>>>>>>>>>> Exporting Process.
>>>>>>>>>>    For this timestamp, any
>>>>>>>>>>                          of the "flowStart" timestamp Information
>>>>>>>>>>                          Elements flowStartMilliseconds,
>>>>>>>>>>                          flowStartMicroseconds, flowStartNanoseconds, and
>>>>>>>>>>                          flowStartDeltaMicroseconds can be used.
>>>>>>>>>>
>>>>>>>>>>     time last flow dropped
>>>>>>>>>>
>>>>>>>>>> The time at which the last Flow Record was
>>>>>>>>>>                          dropped by the Exporting Process
>>>>>>>>>> .  For this
>>>>>>>>>>                          timestamp, any of the "flowEnd" timestamp
>>>>>>>>>>                          Information Elements flowEndMilliseconds,
>>>>>>>>>>                          flowEndMicroseconds, flowEndNanoseconds, and
>>>>>>>>>>                          flowEndDeltaMicroseconds can be used.
>>>>>>>>>>
>>>>>>>>> Again, I do not find these IEs in RFC5102.
>>>>>>>> Same remark, I believe we should be using for the two previous IEs
>>>>>>>> 322    observationTimeSeconds
>>>>>>>> 323    observationTimeMilliseconds
>>>>>>>> 324    observationTimeMicroseconds
>>>>>>>> 325    observationTimeNanoseconds
>>>>>>>> Regards, Benoit.
>>>>>>>>>>     The Exporting Process SHOULD export the Data Record specified by the
>>>>>>>>>>     Exporting Process Reliability Statistics Option Template on a regular
>>>>>>>>>>     basis or based on some export policy.  This periodicity or export
>>>>>>>>>>     policy SHOULD be configurable.
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> (*) regarding the meteringProcessId, we were hesitating between the meteringProcessId and the cache id
>>>>>>>>>> 1. there is a meteringProcessId in IPFIX IANA while there is no cache id
>>>>>>>>> meteringProcessId should do the job.
>>>>>>>>>
>>>>>>>>>> 2. if the IPFIX exporter is configured from [IPFIX-CONF], what should be the value in meteringProcessId?
>>>>>>>>>>      [IPFIX-CONF] doesn't mention the meteringProcessId, but a cache name.
>>>>>>>>>>      From figure 1 and 2, it seems that there is a one to one matching between the cache and the metering process.
>>>>>>>>>>      If this is the case, a solution could be to add a meteringProcess inside the cache in the figure 12 in [IPFIX-CONF] below
>>>>>>>>> See reply to Pauls mail.
>>>>>>>>>
>>>>>>>>> Regards,
>>>>>>>>> Gerhard
>>>>>>>>>
>>>>>>>>>> 4.3.  Cache Class
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>      +-----------------------------------+
>>>>>>>>>>      | Cache                             |
>>>>>>>>>>      +-----------------------------------+        1 +------------------+
>>>>>>>>>>      | name                              |<>--------| immediateCache/  |
>>>>>>>>>>      | dataRecords {readOnly}            |          | timeoutCache/    |
>>>>>>>>>>      | cacheDiscontinuityTime {readOnly} |          | naturalCache/    |
>>>>>>>>>>      |                                   |          | permanentCache   |
>>>>>>>>>>      |                                   |          +------------------+
>>>>>>>>>>      |                                   |
>>>>>>>>>>      |                                   |     0..* +------------------+
>>>>>>>>>>      |                                   |--------->| ExportingProcess |
>>>>>>>>>>      +-----------------------------------+          +------------------+
>>>>>>>>>>
>>>>>>>>>>                            Figure 12: Cache class
>>>>>>>>>>
>>>>>>>>>> What do you think? Do you see another way?
>>>>>>>>>>
>>>>>>>>>> Regards, Paul&   Benoit.
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> _______________________________________________
>>>>>>>>>> IPFIX mailing list
>>>>>>>>>>
>>>>>>>>>> [e-mail]
>>>>>>>>>> https://www.ietf.org/mailman/listinfo/ipfix
>>>>>>>> _______________________________________________
>>>>>>>> IPFIX mailing list
>>>>>>>>
>>>>>>>> [e-mail]
>>>>>>>> https://www.ietf.org/mailman/listinfo/ipfix
>>>>>>>
>>>>>>> _______________________________________________
>>>>>>> IPFIX mailing list
>>>>>>>
>>>>>>> [e-mail]
>>>>>>> https://www.ietf.org/mailman/listinfo/ipfix
>>>>> _______________________________________________
>>>>> IPFIX mailing list
>>>>> [e-mail]
>>>>> https://www.ietf.org/mailman/listinfo/ipfix
>>> _______________________________________________
>>> IPFIX mailing list
>>> [e-mail]
>>> https://www.ietf.org/mailman/listinfo/ipfix
> _______________________________________________
> IPFIX mailing list
> [e-mail]
> https://www.ietf.org/mailman/listinfo/ipfix