Recovering IPv4 Address Space

by Leo Vegoda on February 6, 2008

More IPv4 /8s returned to an “IANA – Reserved” status in 2007 then ever before.

With help from the Regional Internet Registries, three /8s were returned in 2007 and last month we recovered one more. We now have 43 unallocated /8s. Here’s a table showing the details of the returned blocks.

/8 Year Help from
46 – BBN 2007 BBN and ARIN
49 – US DoD 2007 ARIN
50 – US DoD 2007 ARIN
14 – Public Data Net 2008 Network Operators

Despite this windfall we are unlikely to see any more whole /8s returned to the IANA free pool. Our investigations indicate that the other legacy “Class A” assignments are all at least partially used. Recovering the space in those blocks would require large companies to engage in expensive renumbering exercises.

But more importantly, it would not buy us very much time. We allocated more than one /8 per month in 2007, so to gain even one year would require a huge amount of renumbering by the users of more than a dozen legacy assignments.

Geoff Huston’s mathematical projection suggests the IANA free pool will be empty before the second half of 2011 and the RIRs’ pools will run out barely a year later. Of course, whatever mathematical models he uses, he cannot account for the very human possibility of a run on the bank.

Address recovery cannot extend the life of the IANA free pool by more than a few months.

It is possible that unused portions of the legacy “Class A” and “Class B” will be returned to the RIRs free pools. Alternatively, it is possible people with partially used legacy assignments will wait for a variant on the policy proposals in the RIPE and APNIC communities to emerge and then engage in remunerated renumbering and address transfer programs.

Whatever actually happens in the next few years, we can be sure that anyone needing large amounts of address space for a rapidly growing network will have to deploy IPv6. IPv6 deployment in the Internet’s core infrastructure is continuing and network operators at ISPs and enterprises need to plan for a world where their users will need to communicate with systems on both IPv4 and IPv6.


Anonymous 02.06.08 at 12:53 pm

I guess the Fastweb users in southern Milano (Italy) will begin to have problems, as soon as the net will be sued to assign new addresses… (as Fastweb is used to use “reserved” address pools for its users, as the whole network is behind a NAT)

Leo Vegoda 02.07.08 at 3:22 am

We have noticed that some networks use address space that has not been allocated. This is unfortunate as all the unicast IPv4 address space will be allocated, eventually. Using space that is properly allocated elsewhere is likely to cause problems and increase support costs. To some extent this is already the case.

ICANN staff has developed a way of measuring some (but not all) use of unallocated IPv4 address space. As John wrote a few weeks ago, we can measure the queries received at We have used this to begin begin measuring the problem.

We are continuing to work on this topic and I hope we can write a blog article with some details fairly soon.

贵州酒店 02.07.08 at 10:36 pm

I are looking forword the IPv6 to be deployed

network admin 02.08.08 at 12:27 pm

one thing i need to have clarified for myself. why is it so difficult to implement proper subnetowrking to save the ip addresses and have lots of ip addresses left when you can have over 30 billion ip addresses possible…. it is baffling me as to why there is this much stress over something that is very simple to fix…

Leo Vegoda 02.09.08 at 11:26 am

I’m not sure what you mean. IPv4 has just 4 billion addresses, not 30 billion. This isn’t enough to address the Internet if everyone in the world has access.

IPv6 has far more addresses (about 340 trillion trillion trillion) but it is not backwards compatible with IPv4 and so the transition requires using both IPv4 and IPv6 at the same time. Unfortunately, that is expensive and does not generate any additional income for ISPs and other network operators. And so take-up has been so slow.

When the IANA and RIR IPv4 free pools are empty, ISPs and other network operators will probably find it very expensive to obtain additional IPv4 space and IPv6 will become more attractive. But deploying IPv6 means making changes to a lot of systems. As an example of the sorts of changes that need to happen, when Randy Bush added IPv6 to his network he found that he had problems with DNSBLs not supporting IPv6 addresses. There were problems with other software, too.

There’s a lot of work still to be done.

Jay Daley 02.10.08 at 8:08 pm

You do not seem to be acknowledging the important political dimension to this. There is a strong perception in parts of the developing world that the /8 allocations to US corporations are inherently unfair. Particularly as it is clear that only small parts of this address space are publicly routed.

So whilst reclaiming this space might only buy a year or two at the most, it would go a long way towards showing that management of address space by IANA and the RIRs is equitable and inclusive and there is no need for alternate arrangements.

BTW one or two years could actually make a huge difference in the ability of companies to plan the capital expenditure.

Leo Vegoda 02.11.08 at 3:35 am

Jay, which space are you referring to when you say “reclaiming this space might only buy a year or two at the most”? The space I wrote about in this blog post probably extends the life of the IANA free pool by no more than three months. The other legacy /8 assignments are all at least partially used.

The RIRs were allocated 13 /8s last year. That means that even if the demand for space does not increase, buying one year would involve recovering almost one third of the legacy assigned space from networks that are actively using it.

You seem to be proposing that legacy assignments should be reclaimed even though they are in use. Is that right?

Michele 02.11.08 at 5:54 pm

We’ve been trying to encourage companies both big and small to IPv6 enable content websites here in Ireland. So far we’ve had a reasonable level of interest and one commercial site has made the move:



Larry Seltzer 02.14.08 at 6:03 am


I don’t want to go too far with Jay Daley’s argument (I think he’s making more of an equity argument rather than saying that it would meaningfully extend the life of the IPv4 pool), but I have a question about those legacy assignments.

You point out that many of these old /8 networks are at least partially assigned; assuming the allocations were organized enough for this, could the /8 be reclaimed and the assigned parts reassigned as /16s or something else lesser? How much work would that really be?

Leo Vegoda 02.15.08 at 1:37 am


The difficulty involved in reclaiming portions of a legacy /8 depend on how it has been used. In some cases it could be relatively easy to free up large, contiguous blocks and in other cases the space is highly fragmented.

The technical problems can doubtless be solved with time and money. I think the other issue is the incentive for the user of the address space to go through the renumbering process.

Three RIRs are discussing proposals to introduce mechanisms to allow the transfer of address blocks between their members. (A new proposal was introduced in ARIN). Perhaps those policies (if they are agreed) will provide that incentive?


Comments on this entry are closed.