Shane,
On 2009-08-07 01:40, Shane Amante wrote:
> Brian,
>
> On Aug 5, 2009, at 22:19 MDT, Brian E Carpenter wrote:
>> On 2009-08-06 05:34, Christopher Morrow wrote:
>> ...
>>>> 2) Removing other "gems" (or clarifying them) like the second
>>>> sentence in
>>>> the following:
>>>> ---cut here---
>>>> IPv6 nodes MUST NOT assume any mathematical or other properties of
>>>> the Flow
>>>> Label
>>>> values assigned by source nodes. Router performance SHOULD NOT be
>>>> dependent
>>>> on the
>>>> distribution of the Flow Label values. Especially, the Flow Label
>>>> bits alone
>>>> make
>>>> poor material for a hash key.
>>>> ---cut here---
>>>
>>> 'flow label bits alone make a poor material for a hash key'... isn't
>>> this the reverse of saying that we'll (operators) require vendors to
>>> use flow-label for hashing on ECMP/LAG? If so, then... I don't think
>>> flow-label's going to cut it.
>>
>> Please note the word "alone" in the above extract from RFC3697.
>
> I think Chris may have read that a little too fast. :-) I wasn't
> concerned with the third sentence in the RFC, that makes sense and is
> clear. However, my concern was pertaining to the 2nd sentence,
> specifically: "Router performance SHOULD NOT be dependent on the
> distribution of the Flow Label values". Specifically, if Flow Label
> values ARE used as one of the input-keys (in addition to src/dst IPv6
> addresses), then the "distribution" of Flow Label values matters /a lot/
> in order to achieve "good" load-balancing over LAG/ECMP paths and,
> consequently, good router performance. However, perhaps I'm
> misreading/misunderstanding that 2nd sentence. Can you clarify it's
> intent?
Pekka just did that, I think - the flow label will add value if it happens
to increase the randomness of the hash, but this can't be relied on
so we shouldn't depend on it.
Brian
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