Hi Joel,
On Aug 4, 2009, at 10:51 PM, Joel M. Halpern wrote:
The problem is not what the ITRs and ETRs use the field for. They
could / can use the field.
The problem is that the UDP header was introduced specifically so
that different flows would be different in a place that the routers
would look when doing ECMP calculations.
And the router to date do not use the flow label.
Preliminary indications are that routers also won't use UDP-lite,
because it is a different protocol, and they don't know it has port
numbers.
The simple path forward is to allow UDP with 0 checksum.
If that is incorrect, then finding the correct path forward is going
to be hard.
We're talking about the ECMP calculations in _IPv6_ routers here,
right? Do you really believe that enough IPv6 routers have shipped
with this sort of ECMP behavior in _hardware_ that we need to consider
that legacy deployment? I'm somewhat skeptical that this could be the
case... If we're going to make design compromises to deal with
currently-deployed hardware, I'd like to see some evidence that this
hardware actually exists in numbers that are worth considering.
Note, I'm not asking how many routers have been shipped that support
IPv6, nor am I asking whether those routers support ECMP (in
software). I'm not even asking whether some router vendors have taped
out versions of silicon that are so inflexible that they will only
support IPv6 ECMP using UDP ports (not the flow label or UDP-Lite)...
What I am asking is whether IPv6 routers containing that silicon exist
in real-world deployments in large enough numbers that they should be
considered in our design choices.
Thoughts?
Margaret
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