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

Owen DeLong owen at
Tue Jan 25 16:28:03 CST 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 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.


More information about the NANOG mailing list