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.
Joel
Brian E Carpenter wrote:
Hi Joel,
On 2009-08-05 03:08, Joel M. Halpern wrote:
It has become clear with the passage of time that the description of the
flow label in the original IPv6 specs served only to convince everyone
not to use that field for anything. Even now, no one is sure what to do
with it.
If you're referring to the lame appendix to RFC2460, that's exactly
why we wrote RFC3697. My understanding is that some stacks do set the
flow label according to the SHOULD in RFC3697, but I'm not aware
of any deployed use cases (such as load balancing routers). The gap
is not in the basic specs but in exploitation. It's very similar to
what happened with the IPv4 TOS byte, and that took 20 years before
we (a) defined it properly and (b) began to see limited deployment,
as corporate VoIP took off.
My expectation has always been that exploitation of the flow label
would stay on the back burner until IPv6 deployment reached a
significant level, because there isn't much benefit in optimising
flow handling for <1% of the traffic. So I don't really see anything
odd in the current situation.
That said, I can't see any reason why ITRs and ETRs can't use
the flow label among themselves, in a way completely compatible
with RFC3697. But if their hardware engines can't include the
flow label in the n-tuple, that's a problem.
Brian
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