Subject: Re: Preliminary report on flow label hash algorithms

From: RJ Atkinson <[email-masked]>
Date: Mon, 6 Jun 2011 12:39:04 -0400

I would be reluctant to advocate use of a hash algorithm
as computationally expensive as MD5() for generating an
IPv6 Flow Label.  

My sense is that a thoughtful implementer likely would
choose the least computationally expensive algorithm
that would suffice to generate a Flow Label value 
suitable for load-balancing purposes.  

As a use case, one might consider some sort of content server 
with very large numbers of short-lived TCP sessions.  If an
expensive algorithm (e.g. MD5()) were used in that case, 
then the effort to compute the flow label might be am
interesting fraction of "new TCP session creation" overhead.
In turn, this might impair the scalability of that content
server.

In any event, I'm quite comfortable with Brian's current
approach to document a possible algorithm that ought to
suffice without mandating any particular algorithm.
This really is a situation where the details are best
left to implementers (since no interoperability issue 
would arise from different implementations using different
algorithms).

Yours,

Ran

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From: Bob Hinden <[email-masked]>
Date: Mon, 6 Jun 2011 16:22:13 -0700

Ran,

> In turn, this might impair the scalability of that content

I suppose one could precompute a bunch ahead of time, but I agree with your comment.  It's a good point.

> would arise from different implementations using different

I also agree.

Bob

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From: Brian E Carpenter <[email-masked]>
Date: Tue, 07 Jun 2011 11:44:16 +1200

below...

>> would arise from different implementations using different

I sort of agree, if we're talking about my proposed replacement algorithm
However, I would want to weaken the language in the appendix to make it clear
that better algorithms can and will be found - I've had to break off my
experiments for a few weeks due to travel, but there is a lot of scope
for improvement. Anyway, let's see what the AD thinks.

    Brian