That MPLS with 6PE is a superior migration scenario.
Or perhaps, that defining migration scenarios without the full
involvement of network operations people is an exercise in futility.
If the lesson we have learned is that the only practical way
to handle and route IP (whether v4, v6, or otherwise)
requires the use of an underlying virtual circuit layer, then
much of what we are doing in the IETF involves an
architectural delusion about the fundamental datagram and
packet model of the Internet.
All that the IETF can do is to put the technology on the table. It is up
to network operators, public and private (and very private) to try it
out, test the limits, point out bugs to be fixed, and ultimately accept
or reject it. Over the past 8 or 9 years, this is just what many
operators have been doing with MPLS and the verdict is that MPLS works
very well indeed. Unfortunately, we have been a bit shortsighted in not
realizing that we cannot live with only MPLS and IPv4 because we will
run out of new IPv4 addresses by 2010.
But, given that MPLS works and works very well, it seems to me that a
viable migration scenario is NOT to throw away MPLS and attempt to make
pure IPv6 work right away, but to start with 6PE at the edge where most
growth occurs (in terms of connections) and where we can run a viable
business selling IPv6 services to financially support migration
activities.
Yes, if a network does not use MPLS at all today, it may well be wiser
for them to move to dual-stack throughout. But where MPLS is in place,
it seems to me wiser to leverage it for now, limit the impact of IPv6 on
the network, and climb the learning curve. Along the way, we may well
gain confidence that MPLS is not needed because a pure IPv6 network can
do everything that is needed. I suspect that if we get to that point, it
will only be through some additional IETF work to cover gaps that MPLS
covers adequately today.
It is not unusual for movement forward to happen, two steps backward,
three steps forward.
Maybe we are all deluded and that, as has occasionally been
claimed by some telco-based bodies, datagram networks are
only useful for research and the future, as well as the past, of
"real" networks lies in end-to-end circuits. But I'm not
convinced yet.
John, we are more in agreement than disagreement. But you must realize
that a business has to protect its customers and that often means
keeping old technology running longer than leading edge developers would
like. But eventually, the risk of hanging on to old ways rises and
people find a way to upgrade themselves and leverage that upgrade for
financial gain. MPLS technology happens to be in its prime right now, so
that rising risk is many years down the road. We will run out of IPv4
addresses before MPLS runs out of steam.
As a result, many network operators must plan for running both MPLS and
IPv6 services. Eventually, IPv4 services that require MPLS features may
be converted to IPv6 services that can run without MPLS. Just getting
rid of overlapping RFC 1918 ranges helps a lot here.
It seems to me that recommending MPLS with 6PE as a migration strategy
to IPv6 does not rule out pure IPv6 networks sometime in the future.
--Michael Dillon
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