Using IPv6 with prefixes shorter than a /64 on a LAN

Tue Jan 25 22:28:03 UTC 2011

On Jan 25, 2011, at 2:21 PM, Leo Bicknell wrote:

> In a message written on Tue, Jan 25, 2011 at 05:07:16PM -0500, Valdis.Kletnieks at vt.edu wrote:
>> To burn through all the /48s in 100 years, we'll have to use them up
>> at the rate of 89,255 *per second*.
>> 
>> That implies either *really* good aggregation, or your routers having enough
>> CPU to handle the BGP churn caused by 90K new prefixes arriving on the Internet
>> per second.  Oh, and hot-pluggable memory, you'll need another terabyte of RAM
>> every few hours.  At that point, running out of prefixes is the *least* of your
>> worries.
> 
> If you were allocating individual /48's, perhaps.  But see, I'm a
> cable company, and I want a /48 per customer, and I have a couple
> of hundred thousand per pop, so I need  a /30 per pop.  Oh, and I
> have a few hundred pops, and I need to be able to aggreate regionally,
> so I need a /24.
> 
> By my calculations I just used 16M /48's and I did it in about 60
> seconds to write a paragraph.  That's about 279,620 per second, so
> I'm well above your rate.
> 
How soon do you expect your $CABLECO to need to come back
to the RIR for their next /24?

That is the meaningful number. The fact that it took you 60 seconds
to use a /24 to retrofit a network that was built over decades really
isn't a useful measure of utilization rate.

> To be serious for a moment, the problem isn't that we don't have
> enough /48's, but that humans are really bad at thinking about these
> big numbers.  We're going from a very constrained world with limited
> aggregation (IPv4) to a world that seems very unconstrained, and
> building in a lot of aggregation.  Remember the very first IPv6
> addressing proposals had a fully structured address space and only
> 4096 ISP's at the top of the chain!
> 
Yep... Proposal 121 is intended to help address this problem (the
humans are bad at math and big numbers problem).

> If we aggregate poorly, we can absolutely blow through all the space,
> stranding it in all sorts of new and interesting ways.
> 
We may or may not blow through the space, but, we certainly can
easily render the space we do blow through useless.

Owen