IPv4, which are IPs in the form xxx.xxx.xxx.xxx which you're probably familiar, has long known to be running out, hence the development of IPv6 (format xxxx:xxxx:xxxx:xxxx:xxxx:xxxx:xxxx:xxxx).
Quote:One of our readers, Mike, pointed out a certitifed letter that his organization received from ARIN. The letter was sent to CEOs and company executives over the past two weeks. It suggests that new allocations of IPv4 address blocks will not be available in about two more years at the current rate of depletion. It advises organizations needing IP space to do the following:
You should begin planning for IPv6 adoption if you are not doing so already. One of the most important steps is to make your organization’s publicly accessible resources (e.g. external web servers and e-mail servers) available via IPv6 as soon as possible. This will maintain your Internet connectivity during this transition. For more information on IPv6, please refer to ARIN’s online IPv6 Information Center
ARIN is taking additional steps to ensure the legitimacy of all IPv4 address space requests. Beginning on or after 18 May 2009, ARIN will require applications for IPv4 address space to include an attestation of accuracy from an organizational officer. This ensures that organizations submitting legitimate requests based on documented need will have ongoing access to IPv4 address space to the maximum extent possible.