[arin-ppml] Routing table growth, was Re: IPv4 is depleted today

Iljitsch van Beijnum iljitsch at muada.com
Wed Sep 3 10:42:24 EDT 2008

On 3 sep 2008, at 16:17, Howard, W. Lee wrote:

> before the
> inflation of the routing table presumed in this thread?

I must have missed that... What was said about that?

The only way the routing table is going to grow significantly faster  
than it has until now when we run out of v4 space is if the people  
that now get blocks of a million addresses are going to string  
together hundreds of small blocks. And they're not going to do that,  
because it's too much work and too expensive. If you're Comcast and  
already have a /8 (from ARIN--not a legacy one!) you can easily take a  
million addresses and NAT that space so you can put 2, 4, 8, 1000  
customers behind each of those addresses without going through complex  
and presumably expensive address acquisitions.

The 90% of the address allocations for small blocks (10% of the space)  
will simply continue in the same way they have for years, someone who  
needs a /24 will get a /24 and not four /26s. Or maybe they'll get  
_one_ /26. This won't impact the routing table growth much, if at all.

>> In other words, IPv6 is not the only choice. The best choice
>> maybe, but don't for an instant imagine that  properly
>> motivated people can't find a way to make the IPv4 Internet
>> continue to grow.

> I do indeed imagine that.  It keeps me awake at night.

You'll be able to go to http://www.google.com/ over IPv4 for a very  
long time. Don't expect do much peer-to-peer communication over IPv4  
in the less immediate future, though.

>> That approaches the real question: IPv6 migration has a cost
>> function and so does IPv4 growth. Where do the cost lines
>> cross? When does it become less expensive to deploy IPv6 and
>> exert the push that brings
>> IPv4 to a close?

>> The plain truth is that we don't have enough data to do
>> better than guess at the answer to that question.

> I agree with your question.  What data would we need?


(That was 5 years ago, BTW.)

>> But we do
>> know that each IPv6 route costs 2 to 3 times as much to
>> implement in the router as an IPv4 route.

Do we? More bits = more expensive, presumably. But where does 2 to 3  
times come from? Note that today we have about 8.4 prefixes per AS for  
v4 and 1.2 for v6.

>> And we know that there is no new magic in IPv6 routing:
>> multihoming still requires a unique global route.

There is an alternative that is especially appropriate for smaller  


>> If I had to guess, I'd guess that the cost lines never cross. Even as
>> IPv4 gets more expensive, it remains more cost effective to
>> squeeze a little more out of it than to attempt an IPv6
>> migration.

It's not the cost: it's the benefits. If it costs $50 to implement v4  
and you can reach 500 sites out of the Alexa top 500, that's $0.10 per  
destination. If v6 is only $40 but you can only reach the 0.4% of the  
Alexa top 500 sites that have IPv6 that's $5 per destination.

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