RE: Follow-up work on NAT-PT

[Christian Huitema <huitema@windows.microsoft.com>]

I don't think that we need to optimize for IPv6 only hosts. In practice, we can expect that IPv6 capable hosts will either be dual stack. Device designers will want to accommodate situations where their device connects to either an IPv6 network, or an IPv4 network. Implementing "dual stack" is not much harder than implementing "IPv6 only", so this is pretty much a no-brainer.

We need to optimize for reliability and operation support. There, we have to reconcile the tension between two goals: networks are simpler and easier to operate if they support one protocol instead of two; and, networks are simpler if they do not rely on complex and error prone gateways.

Is it really more efficient for an ISP to operate an IPv6 only network? If it is, then IPv4 services will have to be provided through some kind of overlay. On the provider side, the overlay will have connect to some IPv4 "gateways" that give access to the global IPv4 service. On the client side, the overlay will extend either all the way to the client itself, or terminate at the "access router".

If we just want to reuse old technology, the overlay can be built with simple tunnels. Access routers routinely support protocols like PPPoA or PPPoE. PPP over IPv6 (PPPo6?) would not be much of a stretch. It would also not look to strange on the ISP side, since after all ISP are quite used to support PPP servers.

If we don't like the hub and spoke nature of PPP, we can of course be creative and build the overlay with some form of automatic tunneling. But I am not sure that the automatic tunneling will actually reduce operation costs, or increase reliability.

-- Christian Huitema