[arin-ppml] is NAT an inevitabile part of IPv4 / IPv6 transition

Jack Bates jbates at brightok.net
Tue Feb 8 21:20:52 EST 2011

On 2/8/2011 7:46 PM, Lee Howard wrote:
> Jason tried to refocus the thread.
> Forget the past fifteen years.  It is past.
> John, Tony, you are saying, "There is no way to avoid extensive deployment of
> large-scale NAT44 in ISP networks"?
> I have a hard time accepting that, since nobody wants it.  It runs contrary to
> everyone's interest.  It is a temporary solution at best, so companies have to
> deal with both LSN and IPv6, instead of just IPv6.  Is everyone really resigned
> to this?

There are already very large mobile networks (and I'm sure wireline) 
that already deploy LSN. If they hadn't, anyone want to guess how much 
sooner we'd have run out? LSN deployment is already past tense. It just 
hasn't hit critical deployment yet.

But since LSN breaks 6to4 direct communications, let me subject you all 
to complete evil (because it was a fun thought exercise).

DNS recursive servers relabel all 2002:: responses as ULA  /16 (random 
8bit). This forces the client 6to4 to send the packets to the anycast 
relay (you have 1 internal to each LSN area), the inbound 6to4 does 
NPTv6 to convert the source 2002:: to your prefix and passes the packet 
towards the public 6to4 relay (sits outside the LSN for talking to 
remote 2002:: networks). The ULA /16 is converted back to 2002::/16 via 
NPTv6 destined outbound.


AAAA  2002: becomes fd8f:

client sends 2002: to 6to4 anycast to reach fd8f:

internal 6to4 anycast relay converts it to 2600:0000:0202:: trying to 
reach 2002: (nat source and destination appropriately)

It routes to your public anycast relay and on to the destination. Coming 
back, it will have to find a remote relay and come back IPv6 to reach 
your internal relay, where it passes back through NAT to change the 
source and destination again.

ULA was chosen for remotes as it's possible to use a /16 to handle a 1:1 
for the entire Internet. That's not necessary on the inside LSN 
addressing as we know the addressing ourselves and can hard code 

Jack (finding new ways to have broken 6to4 in broken IPv4 LSN environments)

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