Excerpt from RFC 2050 3.1 Common Registry Requirements
Because the number of available IP addresses on the Internet is limited, the utilization rate of address space will be a
key factor in network number assignment. Therefore, in the best interest of the Internet as a whole, specific
guidelines have been created to govern the assignment of addresses based on utilization rates.
Although topological issues may make exceptions necessary, the Basic criteria that should be met to receive network numbers are listed below:
25% immediate utilization rate
50% utilization rate within 1 year
The utilization rate above is to be used as a guideline. There may be occasions when the 1 year rate does not fall
exactly in this range.
Organizations must exhibit a high confidence level in its 1 year Utilization rate and supply documentation to justify the
level of confidence. Organizations will be assigned address space based on immediate utilization plus 1 year
projected utilization. A prefix longer than /24 may be issued if deemed appropriate. Organizations with less than 128
hosts will not be issued an IP address directly from The IRs. Organizations may be issued a prefix longer than /24 if
The organization can provide documentation from a registry Recognized ISP indicating the ISP will accept the long
prefix for injection into the global routing system.
Exceptions to the criteria will not be made based on insufficient equipment without additional detailed justification.
Organizations should implement variable length subnet mask (VLSM) internally to maximize the effective utilization of
address space. Address assignments will be made under the assumption that VLSM is or will be implemented.
IP addresses are valid as long as the criteria continues to be met. The IANA reserves the right to invalidate any IP
assignments once it is determined the requirement for the address space no longer exists.
In the event of address invalidation, reasonable efforts will be made by the appropriate registry to inform the
organization that the addresses have been returned to the free pool of IPv4 address space.
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