RFC1883 and ipv6 spec v2

[Steve Deering]

At 12:53 PM -0800 1/5/98, Darrell Newcomb wrote:
> 1) From my understanding the Flow Labels, once assigned by the originating
> node, will remain the same.  This represents a very interesting problem for
> backbone routers, 20-bit's is not very much address space and a backbone
> router could foreseeably encounter two Flow Labels equal randomly generated
> by two different hosts.

The intent is that routers identify flows by the concatenation of the source
address and the flow label, not by the flow label alone.  The requirement
for random selection of flow labels by source nodes is *not* to avoid
duplicate flow labels, but rather to allow any subset of the bits of a flow
label to serve as a pre-computed hash key for more efficient look-up of the
set of possible matching flows.

> Upon discussing this with a friend.  We decided that if the label is changed
> by the router after each hop, that the 20-bits for the label would be
>enough.
> Providing (number of routers)^20th or even more if the Flow Label Table was
> done on a per interface basis.

Yes, there has been some sporadic discussion in the past about redefining some
or all of the flow label space to be used in a hop-by-hop manner, rather than
end-to-end, but the only written-down proposal for such a change expired from
the internet-drafts directories a long time ago.  If the WG receives a solid
proposal for a change of flow label semantics (including addressing the
problem of flow-label allocation to multicast flows across multi-access links),
we will give it serious consideration.  The weasel words at the beginning
of the Flow Labels section of the IPv6 spec are intended to leave open the
possiblity of such changes.

> 3) Is the Flow Label supposed to be used in conjuction with the Hop-by-Hop
> routing options?

The Flow Label is intended to be used with or without any extensions headers.
(However, there aren't any "Hop-by-Hop routing options" defined at present;
the Routing header is not a Hop-by-Hop option.)

Steve