[ppml] My view on IPv4 (was: Re: IPv4 wind-down)

[Ted Mittelstaedt]

>-----Original Message-----
>From: ppml-bounces at arin.net [mailto:ppml-bounces at arin.net]On Behalf Of
>Iljitsch van Beijnum
>Sent: Monday, April 02, 2007 2:52 PM
>To: Sean Reifschneider
>Cc: ppml at arin.net
>Subject: Re: [ppml] My view on IPv4 (was: Re: IPv4 wind-down)
>
>
>
>This is very true, and will largely remain true as IPv4 space runs  
>out. People who have IPv4 space today won't have a problem, it's the  
>people who need more address space when there no longer is any who  
>will be in a bind, because at that point, the vast majority of all  
>internet users will still only be reachable over IPv4. This means  
>massive amounts of NAT. This is not the nice, friendly NAT where you  
>have three PCs behind your Linksys DSL router and you get to forward  
>ports so fussy applications like VoIP still work.
>
>It will be the kind of NAT where a service provider puts 10, 100 or  
>even 1000 customers behind a single IP address, and the number of  
>usable TCP ports starts being a problem. Forget about port mappings  
>and hence any applications that are more complex than client-server. 

I'm not sure that this is going to be the sticking point with IPv6-IPv4
NAT.

I suspect the real problem is fundamentally this.  Looking out on the
Internet from the IPv4 initiator's point of view, you have a total
number of connectable addresses of X.  However in the IPv6 world the
total connectable number of addresses is Y, and Y is a hell of a lot
bigger than X.  So how do you map a large set to a small set?  Kind
of like wearing a set of eyeglasses with everything but a tiny little
dot on the lenses covered up with paint.

Sure, you can probably do it through any number of schemes, but all
of these are going to be a lot more complicated than the typical NAT
code in an IPv4 NAT today.  And when you add in complexity your going
to decrease reliability and break many specific applications.

On the other hand, if the connection initiator is IPv6 and the Internet
is IPv4 that kind of NAT code should be trivially easy to write.
 
>At that point, those users may want to add IPv6 to their heavily  
>NATed IPv4 so they can run peer-to-peer and server-to-client  
>applications in addition to client-to-server applications. Only at  
>THAT point, it will become interesting for people with enough IPv4  
>space to also support IPv6 so they can talk to those of us who are  
>behind several layers of NAT.
>

It seems to me in your typical "windows-user-on-a-DSL-line" paradigm
that it would be far far easier to have the NAT router dynamically assign
IPv6 only to the Windows user, and the NAT router itself would be 
dual-stacked.


Ted