Problem statement, was: Re: Follow-up work on NAT-PT

[Iljitsch van Beijnum <iljitsch@muada.com>]

On 12 nov 2007, at 4:06, Margaret Wasserman wrote:

> Exactly what types of operational problems exist that we need to  
> solve?

The problem is that there is no operational problem: IPv6 deployment  
can still generously be rounded down to 0.

> Why aren't the existing v4/v6 transition mechanisms sufficient to  
> resolve those problems?  Where are the gaps that needs to be filled?

As per the above, that's a somewhat philosophical question. For a  
large content site deploying IPv6 is non-trivial, and you can't really  
ease into it. So as long as all the users are on IPv4, few of the  
content people are going to do IPv6. You don't need much IPv4 space  
for serving up content so the IPv4 depletion per se isn't going to  
push the content people to IPv6.

For ISPs this is very different: for them, it's much more doable to  
give some of their customers IPv6 without needing to convert the  
infrastructure for their current customers (obviously I'm talking big  
picture here, I'm not saying it's completely trivial). Also, the IPv4  
depletion WILL hit ISPs. The problem is that ISPs can't give their  
customers IPv6-only connectivity while the content is still only  
reachable through IPv4.

Now here's the philosophical issue: is it better to run IPv6-only +  
translation to IPv4, or is it better to have dual stack IPv6 + NATed  
IPv4?

As someone who used to configure routers for a living, my answer is:  
ditch IPv4 in as many corners of your network as possible, routing  
just IPv6 is much simpler. But I don't think this sentiment is  
universally shared.

An argument that many people aren't going to buy into would be that if  
IPv4/NAT and IPv6 must be provisioned separately this probably means  
that in a lot of instances, just IPv4/NAT will be provisioned and even  
with no new IPv4 addresses available we may not see much IPv6 adoption.

Another argument is that if ISPs are going to do NAT, this pretty much  
means that most customers, who run their own NAT, are going to be  
behind two layers of NAT, which is worse than just one layer of NAT.  
The reason for this is that there is no easy way for an ISP to  
provision multiple IPv4 addresses on a single customer link. With  
IPv6+translation you can use DHCPv6 prefix delegation to give users  
enough IPv6 space for all their hosts and only the translator does a  
single round of NAT.

In my opinion, we shouldn't try to get consensus on whether  
IPv6+translation is better than dual stack IPv6+IPv4/NAT, but just go  
ahead and make the best IPv6+translation solution we can and let the  
operators choose what they want to deploy.