Subject: RE: refocusing: what about the flow label?

From: [email-masked]
Date: Fri, 21 Sep 2001 10:47:17 +0300

Michael Thomas wrote:
> 
> Robert Elz writes:
>  > That seems wrong to me.   With a 20 bit field, and a PRNG value in the
>  > field, then there's room for a million different flows, all passing
through
>  > a router, and all being uniquely matched by just the flow label (with
>  > address verification later).  My guess is that a million is already too
>  > small, but it is also most probably not so far away from what's needed
>  > as to be unusable (to use the million we'd need rather more flows than
>  > that, because we know we'll get collisions, which is what saves such a
>  > small number).
>  > 
>  > Your proposal reduces that to 64K flows.   That I know is way too
small.
> 
>    Er, the flow key is src/dst/flowlabel, right? That means it's
>    64k per host pair which seems like plenty.
> 

Unless the current RFC 2460 App.A semantics is changed, the flow key
actually is src/flowlabel, quote:

"A flow is uniquely identified by the combination of a source
 address and a non-zero flow label."

Additionally, the routing behavior for each unique flow must be the same
("All packets belonging to the same flow must be sent with the same source
address, destination address, and flow label..."), so the same flow label
value cannot be used with different destination addresses by a given source.

Obviously these rules do not apply to the flow label value 0, and must be
relaxed for other well-known flows as well.

	Jarno

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From: Robert Elz <[email-masked]>
Date: Fri, 21 Sep 2001 16:44:52 +0700

Date:        Fri, 21 Sep 2001 10:47:17 +0300
    From:        [email-masked]
    Message-ID:  <[email-masked]>

  | "A flow is uniquely identified by the combination of a source
  |  address and a non-zero flow label."

  | Obviously these rules do not apply to the flow label value 0,

Yes, that's what it explicitly says.  If the flow label is not non-zero
(ie: is 0) then it isn't a flow - hence rules for flows can't be relevant.

  | and must be relaxed for other well-known flows as well.

And that is the question that has been being debated...

Right now I think we need to wait and see what Brian comes up with next.

kre