multiple prefixes

Doug Barton dougb at
Tue Feb 12 09:18:27 CET 2013

On 02/12/2013 12:15 AM, Lorenzo Colitti wrote:
> On Tue, Feb 12, 2013 at 2:28 PM, Doug Barton <dougb at
> <mailto:dougb at>> wrote:
>         What I suspect you mean when you say (elsewhere) that ULA+NPT costs
>         nothing is that it costs /you/ (or "the network operator") nothing.
>         But there is a cost, and you've just moved it elsewhere.
>     Can you define what you believe those costs are, and why they are
>     important?
> Higher operational cost caused by more complex, stateful operation of
> the network. Lower reliability due to NAT leading to loss of said state
> and interrupted sessions. Higher capex caused by boxes having to do more
> complex stuff (NAT vs. route). Higher cost and a higher barrier to entry
> for application developers as they each have to re-learn NAT traversal
> (and no, NAT traversal is *not* the same as traversing a stateful
> firewall - that's easier). Lower quality of service when said
> applications perform worse. Believe it or not, Skype on my phone works
> better on the a one-NAT 3G network than on a double-natted 1Gbps fiber
> connection.

What you described were all costs of NAT, no argument.

Now can you please describe how those things are relevant to NPTv6?

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