multiple prefixes

Lorenzo Colitti lorenzo at
Tue Feb 12 09:15:18 CET 2013

On Tue, Feb 12, 2013 at 2:28 PM, Doug Barton <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.
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