Based on calculations that I have recently done, nearly a third of IPv4 address space is not in active use. The IP address calculations refer to consecutive IP blocks not advertised by any of the autonomous systems on the global Internet routing tables, not to individual addresses in existing subnets. This amount seems large and has potentially interesting consequences.
Here is how the math was done: using a script, the IPv4 address space was enumerated, and for each IP address, an ASN lookup is performed using data provided by Route Views. Putting aside the private, multicast and other reserved ranges, I found that out of approximately 14.5 million /24 address blocks, 4.4 million are ‘unrouted’, i.e., not assigned to any autonomous system in BGP routing tables. This amounts to 30.3 percent. The BGP data is from July 30th, 2012. Mapping the unrouted blocks to the IANA address registry, we see that two thirds of the unrouted blocks are in the so-called legacy space.
What makes this figure interesting is that the largest RIRs have announced that their pool of unallocated IPv4 addresses is either exhausted (APNIC) or near exhaustion (ARIN and RIPE-NCC). My calculations show that the lack of unallocated addresses from the RIRs is not quite the same as IPv4 addresses having run out!
What are the implications of the more than one billion allocated yet unused IPv4 addresses? It points to a potentially lucrative IPv4 transfer market for the next few years. We have a resource that has a certain degree of scarcity, yet is in adequate supply to be tradable, and many potential buyers and sellers. This makes the need for transparency and design of efficient market mechanisms more apparent, and could affect the economics of IPv6 deployment in the coming years. (See Geoff Huston’s recent piece for a discussion of depletion rates in relation to IPv6 adoption.)
Written by Hadi Asghari, Delft University of Technology.