On 2010-08-12 11:34, Philip Levis wrote:
> On Aug 10, 2010, at 11:12 PM, Rémi Després wrote:
>
>> Le 10 août 2010 à 18:09, Michael Richardson a écrit :
>>
>>>>>>>> "Rémi" == Rémi Després <[email protected]> writes:
>>> Rémi> RFC 3697 isn't concerned with ASes, and doesn't need to be.
>>> Rémi> The proposal is only that, where load balancing is performed,
>>> Rémi> 0 FLs MAY be replaced by meaningful values for this purpose.
>>> Rémi> A FL, once set to a non 0 value, never needs to be reset.
>>>
>>> okay, so what you are saying is that load balancing uses of the FL are
>>> only upset when they see zero. So for instance, if layer-4s (i.e. end
>>> points) were mandated that they must now always set a FL consistently on
>>> a flow, and set it to a non-zero value, that this would satisfy the
>>> requirements of load balancers.
>> Right.
>>
>> To be even more precise:
>> - Flow endpoints (sometimes layer 4 and sometimes layer 3) should from now
>> on be mandated to set FLs with non-0 values that statistically differ from a
>> flow to another.
>
> The intention is to have a BCP for network stack implementers to follow?
I don't there is a clear intention just yet, but my personal view is coming
round to a 3697bis document, which would presumably be Proposed Standard,
not BCP. But certainly we need more precise normative guidance.
>
>
>> - However, we have to face that, so far, they are generally mandated to set
>> FLs to 0.
>
> I apologize for the lack of context (I'm coming from ROLL): your sentence
> seems to suggest that flow labels today are mandated to be 0. This doesn't
> seem to be right: among other things, ping6 supports setting the flow label,
> and by default allocates a random flow label.[1] Basically, I'm confused if
> you're talking in the present tense of what's done with flow labels today, or
> the future tense of how flow labels should be used in the future.
What 3697 says is
"A Flow Label of zero is used to indicate packets not part
of any flow.
...
A source node which does not assign traffic to flows MUST set
the Flow Label to zero."
It's a little self-referential, since flow *by definition* is
a set of packets with the same flow label (and address pair).
The rule is there to prevent accidental flow labels because
the programmer simply forgot to zero the field.
That being so, it isn't clear to me that we need a mandatory
flow label, although I can make some arguments for a SHOULD.
Brian
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