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

Mark Smith nanog at
Sun Sep 30 01:24:34 UTC 2007

On Sat, 29 Sep 2007 14:45:23 -1000
Randy Bush <randy at> wrote:

> > MPLS as well as the IETF softwires techniques (the MPLS model without
> > using MPLS i.e. tunnel from ingress to egress via automated setup
> > tunnels - gre, l2tp, or native IPv4 or IPv6) can or will shortly be
> > able to be used to tunnel IPv6 over IPv4 or vice versa. softwires in
> > effect treats the non-native core infrastructure as an NBMA layer 2.
> > 
> > The advantage of these techniques verses dual stack is that they push
> > the complexity of dual stack to the network ingress and egress
> > devices.
> > 
> > Dual stack isn't all that complicated, however when you think about 
> > running two forwarded protocols, two routing protocols or an
> > integrated one supporting two forwarded protocols, having two
> > forwarding topologies that may not match in the case of dual routing
> > protocols, and having two sets of troubleshooing methods and tools, I
> > think the simplicity of having a single core network forwarding
> > protocol and tunnelling everyting else over it becomes really
> > attractive.
> huh?  and your tunnels do not have *worse* congruency problems than dual
> stack?  gimme a break.

I do not understand what you mean.

The tunnelled traffic takes the same ingress-to-egress path through the
core that it would if the core natively supported the tunnelled payload

This is the basic BGP/MPLS model, using IPv4, IPv6, GRE or L2TP as the
encapsulation, instead of MPLS. 



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

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