The exhaustion of the IP address space is a topic of concern for the
entire Internet community. This plan for the assignment of Class A,
B, or C IP numbers to network applicants has two major goals:
1) to reserve a portion of the IP number space so that it may be
available to transition to a new numbering plan
2) to assign the Class C network number space in a fashion which
is compatible with proposed address aggregation techniques
The Class A number space can support the largest number of unique
host identifier addresses and is also the class of network numbers
most sparsely populated. There are only approximately 11 Class A
network numbers which are unassigned or unreserved, and these 11
network numbers represent about 9% of the total address space.
The IANA and the IR will retain sole responsibility for the
assignment of Class A network numbers. The upper half of the Class A
number space will be reserved indefinitely (IP network addresses
64.0.0.0 through 127.0.0.0). While it is expected that no new
assignments of Class A numbers will take place in the near future,
any organization petitioning the IR for a Class A network number will
be expected to provide a detailed technical justification documenting
network size and structure. Class A assignments are at the IANA's
discretion.
Previously, organizations were recommended to use a subnetted Class B
network number rather than multiple Class C network numbers. Due to
the scarcity of Class B network numbers and the underutilization of
the Class B number space by most organizations, the recommendation is
now to use multiple Class Cs where practical.
The restrictions in allocation of Class B network numbers may cause
some organizations to expend additional resources to utilize multiple
Class C numbers. This is unfortunate, but inevitable if we implement
strategies to control the assignment of Class B addresses. The
intent of these guidelines is to balance these costs for the greater
good of the Internet.
4.2.1. Organizations applying for a Class B network number should fulfill
the following criteria:
1) the organization presents a subnetting plan which documents
more than 32 subnets within its organizational network
AND
2) the organization has more than 4096 hosts
Organizations applying for a Class B network number must submit an
engineering plan that documents its need for a Class B network
number. This document must demonstrate that it is unreasonable to
engineer its network with a block of class C network numbers. The
engineering plan must include how many hosts the network will have
within the next 24 months and how many hosts per subnet within the
next 24 months.
The submitted engineering plans will be held in strict confidence by
the Internet registries and will only be used to judge whether an
application is justified. If it is deemed that the applicant's
engineering plan, including the number of hosts and subnets, does not
warrant a Class B assignment, the applicant will be allocated a block
of Class C addresses.
There may be some circumstances where the organization is unable to
utilize a block of Class C network numbers and does not meet the
suggested criteria. In such cases, the engineering plan should
clearly demonstrate their inability to utilize a block of Class C
network numbers.
4.2.2. The IR may allocate small blocks of Class B network numbers to
regional registries if so doing will improve the service that is
being provided to the community. The IR may issue more specific
guidelines for the further assignment of the numbers which will be
consistent with the stated guidelines. The IR may require accounting
of the block assignment including receipt of the applicants'
engineering plans. The IR may audit these engineering plans to
confirm that the assignments are consistent with the guidelines.
Section 3 of this document recommends a division of the Class C
number space. That division is primarily an administrative division
which lays the groundwork for distributed network number registries.
This section addresses assignment of network numbers from within
regional block assignments. Sub-allocations of the block to sub-
registries is beyond the scope of this paper.
By default, if an organization requires more than a single Class C,
it will be assigned a bit-wise contiguous block from the Class C
space allocated for its geographic region.
For instance, an European organization which requires fewer than 2048
unique IP addresses and more than 1024 would be assigned 8 contiguous
class C network numbers from the number space reserved for European
networks, 194.0.0.0 - 195.255.255.255. If an organization from
Central America required fewer than 512 unique IP addresses and more
than 256, it would receive 2 contiguous class C network numbers from
the number space reserved for Central/South American networks,
200.0.0.0 - 201.255.255.255.
The IR or the registry to whom the IR has delegated the registration
function will determine the number of Class C network numbers to
assign to a network subscriber based on the subscriber's 24 month
projection of required end system addresses according to the
following criteria:
Organization Assignment
1) requires fewer than 256 addresses 1 class C network
2) requires fewer than 512 addresses 2 contiguous class C networks
3) requires fewer than 1024 addresses 4 contiguous class C networks
4) requires fewer than 2048 addresses 8 contiguous class C networks
5) requires fewer than 4096 addresses 16 contiguous class C networks
6) requires fewer than 8192 addresses 32 contiguous class C networks
7) requires fewer than 16384 addresses 64 contiguous class C networks
If the subscriber's network is divided into logically distinct LANs
across which it would be difficult to use the given number of Class C
network numbers, the above criteria may apply on a per-LAN basis.
For example, if a subscriber has 600 hosts equally divided across ten
Ethernets, the allocation to that subscriber could be ten Class C
network numbers; one for each Ethernet. The subscriber would have to
support the request with to deviate from the stated criteria with an
engineering plan.
These criteria are not intended to cause a subscriber to subnet Class
C networks unneccessarily. Although, if a subscriber has a small
number of hosts per subnet, the subscriber should investigate the
feasibility of subnetting Class C network numbers rather than
requesting one Class C network number for every subnet. In cases
where the lack of Class C subnetting would result in an extravagant
waste of address space, the registries may request an engineering
plan detailing why subnetting is impossible.
If a subscriber has a requirement for more than 4096 unique IP
addresses it could conceivably receive a Class B network number.
However, there are cases where a subscriber may request a larger
block of Class C network numbers. For instance, if an organization
requires fewer than 8192 addresses and requests 32 Class C network
addresses, the regional registry may honor this request. The maximal
block of Class C network numbers that should be assigned to a
subscriber consists of 64 contiguous Class C networks. This would
correspond to a single IP prefix of 18 bits.
Exceptions from the above stated criteria will be determined on a
case-by-case basis.
