NAT v6->v4 and v4->v6 (was Re: WG Action: Conclusion of IP Version 6 )

Mark Smith nanog at
Sun Sep 30 09:07:25 UTC 2007

On Sun, 30 Sep 2007 10:41:01 +0200
Per Heldal <heldal at> wrote:

> On Sun, 2007-09-30 at 11:40 +0930, Mark Smith wrote:
> > The model we're talking about seems to me to be that old model on
> > it's head. The devices at the edge of the core network are fully aware
> > of the underlying topology of the core network so they can make
> > informed forwarding decisions. The tunnelling encapsulation only serves
> > the purpose of transporting protocols/payloads, that aren't native in
> > the core, from edge-to-edge. The tunnelling function doesn't try to
> > control or have to take responsibility for the selecting paths taken
> > across the core.
> This is just is a slight move of the core/edge boundary. Core switching
> capabilities (MPLS) have been added to edge devices which were pure
> terminal-devices from an ATM-perspective. The MPLS-cloud is just as
> obscure as ATM to a non-MPLS-speaking IP-device. 

No it isn't. The MPLS control plane runs IP routing protocols, so even
if an upstream device isn't capable of MPLS forwarding, it still has
visibility to the network topology information both propagated across
and within the MPLS domain. For conventional IP forwarding, MPLS is a
forwarding optimisation, not a forwarding replacement. 



        "Sheep are slow and tasty, and therefore must remain constantly
                                   - Bruce Schneier, "Beyond Fear"

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