don at nz.net

The IPocalypse is upon us. There are seven /8 IPv4 address blocks left! Soon there will be six. Then five.

On that fateful day, when the sixth to last /8 block is assigned, the five Regional Internet Registries (RIRs) will receive one each of the remaining five /8s for final allocation. This will probably happen in the next month or two.

Then there will be no more! Oh woe is us!

Or not. There are a bunch of ways that we can measure IP address space usage. They include:

1. The number of address available. Formally, this is 2^32 minus the 588,514,560 addresses (or just over 35 /8 blocks)that  are assigned for special uses (multicast, reserved, private addressing etc), leaving 3,706,452,736 addresses (or the equivalent of just over  220.9 /8 blocks) available for present or future end-user assignment.
2. The amount of addresses assigned by IANA to RIRs for allocation. Currently, this stands at pretty much all of the above space, less the aforementioned seven /8s (or 117,440,512 addresses).
3. The amount of address space allocated by RIRs. According to Geoff Huston, this is likely, at current rates of assignment, to run out in mid-late 2011.
4. The amount of address space that is actually advertised. Right now, a little under 2/3rds of the allocatable address space (that is, excluding private, multicast and reserved address space) is actually advertised to the global routing table. That’s right, 1/3rd of the IP address space is unequivocally dark.
5. The amount of address space actually allocated to infrastructure. Now things get murky. Is a /8 advertisement actually representing a /8 worth of allocation? Or is the holder of that /8 advertising it simply because they can?
6. The amount of address space actually in use. This too is largely unmeasurable. Many advertisements, especially smaller ones. are to achieve multihoming, in which case a /24 may have very small numbers of hosts actually assigned to it. The nature of IP address assignment is that you always have to allocate a larger subnet than you plan to use, unless you can do single IP address per client allocations, e.g. using PPP & friends, my ARP hack or layer-3 VLAN schemes.

Measurements 1 through 4 are easy. 5 & 6 are hard. All we can say for sure is that each measurement will give a smaller number of addresses in use than the one above. If an address appears on the global routing table, we can follow it to its associated autonomous system, but beyond that, we have to look ad individual addresses, and even then an assigned and in-use address my be behind a firewall or something and effectively invisible but none the less actively in play.

It did occur to me to look at reverse map entries, but experience suggests that these are unhelpful, being fairly universally badly managed.

So, the question of when IP address space will run out remains difficult to answer. Geoff’s IPv4 Address Report shows a curve in address advertisements (fig. 11c) which,although initially exponential, seems to have settled to a linear growth of about 176,000,000 addresses per year in actual advertisements since 2006. If that rate is maintained, the 1.3 billion or so unadvertised addresses should run out in about seven years.

But I suspect that as RIR space becomes unavailable, we’ll start to see address space that is currently advertised but not actually in use being re-allocated (read: sold). For starters, there are about 200 million addresses tied up in non-carrier addresses that are currently advertised as /8s. Admittedly, a goodly chunk of that space may actually be in use, but one suspects that a significant proportion isn’t. There are a lot of equally historical /16 assignments and smaller blocks assigned under multihoming policies that are similarly underutilised, and could shed a large proportions of their advertised allocation as their holders discover it’s worth more to them in someone else’s hands than in their own.

So I’m going to lick my finger and stick it in the wind. I think we have ten years or so before we really, genuinely run out of IPv4 addresses, and that ignores the transition to IPv6 completely. In reality, as IPv4 addresses become scarce (read: expensive), we’ll see folks making do with less and looking harder at IPv6 transition, so I doubt we’ll ever actually run out. Sure, there’s a whole bunch of stuff you can’t do without lots of addresses, but those applications will simply have to go to IPv6.

Don’t get me wrong; I’m not suggesting for a moment that we don’t have to worry. The single thing that will prevent exhaustion is money. Scarce resources have value; the more scarcity, the more value. RIRs have some really hard choices ahead of them; they’re going to be in the firing line to manage the emerging market in IPv4 address space. Pretending that organisations don’t “own” their address space will stop being an option; the court cases haven’t started in earnest yet, but unless the RIRs urgently awake from the fantasy that IP address space is not a tradable asset, they will.

Either they will rise to the challenge, or they’ll swept into irrelevancy. I rather hope the latter doesn’t happen, because the alternative is anarchy. The best we can hope for is that enough wiser heads prevail to ensure that the emerging IP address bourses have sufficient support to ensure that the fabric of the Internet isn’t torn apart by the conflict between those who long for a non-commercial Internet where everyone plays nice, and the immediate needs of a market where folks need to get stuff done.