Re: [IPFIX] Semantic and structured data

[Benoit Claise <[e-mail]>]

Dear all,

We've been thinking about this one, and we see 3 solutions. We believe 
that the solution 3 is the way to go, as we show below.

_Solution 1. _
Consider that the semantic is out of scope for this document.
This is the easiest solution.  However, we understand it's not right: we 
would not do a complete job wrt to IPFIX structured data
As Gerhard was expressing, the collector has not clue how to treat the 
example of a BasicList of egress interfaces in a Flow Record.
     - Has every counted packet been sent on every egress interface?
       => multicast case, AND semantic
     - Has every counted packet been sent on any one of the egress 
interfaces?
      => load balancing case, OR semantic

_Soltution 2_
We could focus on the logical AND and OR semantics only , by defining 
semantic lists, such as andBasicList, andSubTemplateList, 
andSubTemplateMultiList, orBasicList, orSubTemplateList, and 
orSubTemplateMultiList
So 6 I.E.s in total, describing AND and OR semantics.
While it's solved the router and most mediation function needs today, we 
understand that this is not a complete solution.
Gerhard, in one of his old draft, draft-sommer-ipfix-mediator-ext-01, 
proposed ADTs for orderedList, orderedPair, and portRanges which allow 
the definition new IEs for port ranges etc.
Even if this solution 2 is extensible, in the long term, will lead to an 
explosion of IEs: 3 list types * the semantic type, where the semantic 
can be (and, or, orderedList, orderedPair, portRanges, random, etc...)

_Soltution 3
_We propose to add a semantic field in the 3 list types.
Something such as:

     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|               Field ID    |       Element Length            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Semantic  |             BasicList Content ...                 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                           ...                                 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

This semantic field would be a new IANA registry, we could be populated 
initially with NONE, OR, AND, ORDERED, etc... Up to discussion.
The advantage of this solution is that it's extensible, and it doesn't 
need new IEs for each semantic.
If ever required (mainly in a mediation function), we can model  very 
complex semantic, eg, "(eth1 OR eth2) AND (NOT (eth3 OR eth4)) OR 
linecard2", which could be the new observation point from a aggregated 
Flow Record



_Conclusion:_
After much debate internally, we believe that we should do the effort to 
include this semantic now, and not postpone the problem, which will lead 
to an explosion of IEs in the future.
Personally, I was initially against the solution 3 ... mostly due to the 
effort required to modify the complete specs.
We're now ready to modify the specifications in the IPFIX structured 
data, but we would like to get your feedback and agreement in advance as 
this is not a small piece of work.

Please comment.

Regards, Paul, Stan, Gowri, and Benoit.
> hi Benoit, Gerhard,
>
> In this case I'm strongly in favor of leaving semantics out of 
> structured data. Structured data defines containers. The semantics of 
> the containers as a whole and the elements change based upon the 
> information elements within the container and within the record 
> containing it. Wedging semantics into the structured data elements 1. 
> risks further proliferation of (potentially non-interoperable) ways to 
> represent the same thing, 2. gives us more ways to represent 
> nonsensical things (an OR basicList of MPLS stack 
> entries...means...what?), and 3. risks defining an inadequate semantic 
> representation mechanism (what about semantics for records not using 
> structured data? what about ordered versus unordered sets? what about 
> OR basicList vs AND basicList vs nested AND and OR basicLists vs just 
> three identical IEs?). If we really want an unambiguous semantic 
> framework for IPFIX (and here I'm not convinced either way) that's 
> best done on its own, addressing things at the information element and 
> record level. Doing it here confuses the issue.
>
> Regards,
>
> Brian
>
> On Nov 10, 2009, at 6:26 AM, Benoit Claise wrote:
>
>> Gerhard,
>>
>> Thanks for your email.
>> I have no strong feelings about the two solutions you proposed.
>>
>> From a pure router point of view,  I don't see any use cases for 
>> logical OR in exporting flow records.
>> However, from a IPFIX Mediator point of view, I see some use cases.
>> I mean that it requires an Intermediate Aggregation Process or 
>> Intermediate Correlation Process to express: I've seen this flow 
>> record OR that flow record.
>> Now, it's true that even routers will have mediation functions...
>>
>> I'm inclined to add orBasicList, orSubTemplateList, 
>> orSubTempalteMultiList to the draft (This is a small addition after 
>> all) and to express that, by default, a logical AND is assumed... 
>> specifically if the structured data is used in the IPFIX Mediation 
>> Protocol.
>>
>> I'm not convinced by the NOT in the context of structured data, as we 
>> don't even have a concept of NOT for a single information element!
>>
>> I would like to get some more feedback from others.
>>
>> Regards, Benoit.
>>
>>> Dear all,
>>>
>>> Regarding draft-ietf-ipfix-structured-data, I see the risk that the
>>> semantic of the exported structured data is not clear.
>>>
>>> How do you interpret the manifold occurrence of the same Information
>>> Element (basicList) or the same group of Information Elements
>>> (subTemplateList) in one record?
>>>
>>> What does it mean if basicList, subTemplateList, or 
>>> subTemplateMultiList
>>> is used for a Flow Key field? Or non-key field?
>>>
>>> Some Examples:
>>>
>>> - BasicList of egress interfaces in a Flow Record
>>>  How should a Flow Record be interpreted which contains a list of
>>>  egress interfaces and a packet counter?
>>>  Has every counted packet been sent on every egress interface?
>>>    => multicast case, AND semantic (see example in section 8.1)
>>>  Has every counted packet been sent on any one of the egress
>>>  interfaces?
>>>    => load balancing case, OR semantic
>>>  Can it be used as a Flow Key or not?
>>>
>>> - BasicList of destination ports in a Flow Record
>>>  As every packet has only one destination port, the only reasonable
>>>  interpretation is that the Flow contains packets having one of
>>>  the reported port numbers.
>>>    => OR semantic
>>>  This would be a non-key field.
>>>
>>>
>>> I think there are two solutions:
>>>
>>> 1. We decide that the semantic of list content is out of scope of
>>>   draft-ietf-ipfix-structured-data. We add a note to the draft that
>>>   the semantic must be clear from the context or the definition of the
>>>   Information Elements used within the lists.
>>>
>>> 2. We define semantic lists, such as
>>>   - andBasicList, andSubTemplateList, andSubTemplateMultiList
>>>   - orBasicList, orSubTemplateList, orSubTempalteMultiList
>>>   describing AND and OR semantic of the contained IEs/Templates,
>>>   respectively.
>>>
>>>
>>> As I wrote in an earlier mail, I see a good use case for 
>>> orBasicList. It
>>> could be used in the Selector Report Interpretation of Property Match
>>> Filtering to report a filter like "port 80 or port 443".
>>> http://www.ietf.org/mail-archive/web/ipfix/current/msg04856.html
>>> At the moment, the Selector Report Interpretation is limited to AND.
>>> However, if we also want to express a NOT, we still need another 
>>> solution...
>>>
>>> Regards,
>>> Gerhard
>>>
>>> _______________________________________________
>>> IPFIX mailing list
>>> [e-mail]
>>> https://www.ietf.org/mailman/listinfo/ipfix
>>>
>>
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