Thanks to Rob for reminding me of IPv4 auction websites again. I looked at them a couple years ago, but there was very little real activity at the time. Looks like that has changed now. ARIN is essentially out of IPv4 space, and very restrictive in handing out any addition addresses. It has gotten very hard, if not impossible, to obtain a larger block of IPv4 space. So no surprise that markets for IPv4 space are coming up. 

These markets are not in line with registrar policies [1]. If someone receives an IP address assignment, then they don't technically "own" the addresses. Once they are no longer needed, they are supposed to be returned to ARIN to be handed to the next applicant in line. But there has been little enforcement, and there have always been grey areas. For example, a company may buy another company, and in the process obtain access to that companies IP address space. Later, assets other then the IP address space could be sold off, leaving the buy with the rights to the IP address space.

Here are some of the sites offering IP address space (I am not endorsing them, and have no idea how "real" they are):

- ipv4auctions.com. Currently three offers for space up to a /20 at $7-$10 per address. There are a couple of bids.
- ebay.com. There are a number of auctions with IP addresses for sale and for rent. Looks like they are going for about the same price as the addresses at ipv4auctions.com [2]

Some sites have dones so in the past, but already shut down (e.g. tradeipv4.com). In other cases, the nanog mailing list was used to offer IP address space, or IP addresses were purchased as part of bankruptcy auctions [3]

[1] http://www.internetsociety.org/internet-society-open-letter-transfer-internet-protocol-addresses
[2] http://www.ebay.com/itm/IP-Address-22-Routable-IP-Block-Four-Class-C-For-Sale-or-Rent-/181769443467?pt=LH_DefaultDomain_0&hash=item2a524d988b
​[3] http://www.maximumpc.com/borders-sells-65536-ipv4-addresses-for-12-each/​

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Johannes B. Ullrich, Ph.D.
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