Network Working Group K. Hubbard
Request for Comments: 2050 M. Kosters
Obsoletes: 1466 InterNIC
BCP: 12 D. Conrad
Category: Best Current Practice APNIC
November 1996 INTERNET REGISTRY IP ALLOCATION GUIDELINES
Status of this Memo
This document specifies an Internet Best Current Practices for the
Internet Community, and requests discussion and suggestions for
improvements. Distribution of this memo is unlimited.
By approving this document as a Best Current Practice,the IESG
asserts its belief that this policy described herein is an accurate
representation of the current practice of the IP address registries
with respect to address assignment. This does not constitute
endorsement or recommendation of this policy by the IESG. The IESG
will reevaluate its approval of this document in December 1997 taking
into consideration the results of the discussions that will be take
place in the IRE Working Group between now and then.
This document describes the registry system for the distribution of
globally unique Internet address space and registry operations.
Particularly this document describes the rules and guidelines
governing the distribution of this address space.
This document describes the IP assignment policies currently used by
the Regional Registries to implement the guidelines developed by the
IANA. The guidelines and these policies are subject to revision at
the direction of the IANA. The registry working group (IRE WG) will
be discussing these issues and may provide advice to the IANA about
This document replaces RFC 1466, with all the guidelines and
procedures updated and modified in the light of experience.
This document does not describe private Internet address space and
multicast address space. It also does not describe regional and
local refinements of the global rules and guidelines.
This document can be considered the base set of operational
guidelines in use by all registries. Additional guidelines may be
imposed by a particular registry as appropriate.
Table of Contents
1. Introduction.......................................22. Allocation Framework...............................42.1 Guidelines for Internet Service Providers.........42.2 Submission of Reassignment Information............63. Assignment Framework..............................73.1 Common Registry Requirements......................73.2 Network Engineering Plans.........................83.3 Previous Assignment History.......................93.4 Network Deployment Plans..........................93.5 Organization Information..........................93.6 Expected Utilization Rate.........................104. Operational Guidelines for Registries.............105. In-Addr.Arpa Domain Maintenance...................116. Right to Appeal...................................117. References........................................128. Security Considerations...........................129. Authors' Addresses................................131. Introduction
The addressing constraints described in this document are largely the
result of the interaction of existing router technology, address
assignment, and architectural history. After extensive review and
discussion, the authors of this document, the IETF working group that
reviewed it and the IESG have concluded that there are no other
currently deployable technologies available to overcome these
limitations. In the event that routing or router technology develops
to the point that adequate routing aggregation can be achieved by
other means or that routers can deal with larger routing and more
dynamic tables, it may be appropriate to review these constraints.
Internet address space is distributed according to the following
1) Conservation: Fair distribution of globally unique Internet address
space according to the operational needs of the end-users and Internet
Service Providers operating networks using this address space.
Prevention of stockpiling in order to maximize the lifetime of the
Internet address space.
2) Routability: Distribution of globally unique Internet addresses
in a hierarchical manner, permitting the routing scalability of
the addresses. This scalability is necessary to ensure proper
operation of Internet routing, although it must be stressed that
routability is in no way guaranteed with the allocation or
assignment of IPv4 addresses.
3) Registration: Provision of a public registry documenting address
space allocation and assignment. This is necessary to ensure
uniqueness and to provide information for Internet trouble shooting
at all levels.
It is in the interest of the Internet community as a whole that the
above goals be pursued. However it should be noted that
"Conservation" and "Routability" are often conflicting goals. All
the above goals may sometimes be in conflict with the interests of
individual end-users or Internet service providers. Careful analysis
and judgement is necessary in each individual case to find an
The Internet Registry system
In order to achieve the above goals the Internet Registry (IR)
hierarchy was established.
The Internet Registry hierarchy consists of the following levels
of hierarchy as seen from the top down: IANA, Regional IRs, Local
The Internet Assigned Numbers Authority has authority over all
number spaces used in the Internet. This includes Internet
Address Space. IANA allocates parts of the Internet address space
to regional IRs according to its established needs.
Regional IRs operate in large geopolitical regions such as
continents. Currently there are three regional IRs established;
InterNIC serving North America, RIPE NCC serving Europe, and AP-
NIC serving the Asian Pacific region. Since this does not cover
all areas, regional IRs also serve areas around its core service
areas. It is expected that the number of regional IRs will remain
relatively small. Service areas will be of continental
Regional IRs are established under the authority of the IANA.
This requires consensus within the Internet community of the
region. A consensus of Internet Service Providers in that region
may be necessary to fulfill that role.
The specific duties of the regional IRs include coordination and
representation of all local IRs in its respective regions.
Local IRs are established under the authority of the regional IR
and IANA. These local registries have the same role and
responsibility as the regional registries within its designated
geographical areas. These areas are usually of national
2. Allocation Framework
2.1 Guidelines for Internet Service Providers (ISPs)
This document makes a distinction between the allocation of IP
addresses and the assignment of IP addresses. Addresses are
allocated to ISPs by regional registries to assign to its customer
ISPs who exchange routing information with other ISPs at multiple
locations and operate without default routing may request space
directly from the regional registry in its geographical area. ISPs
with no designated regional registry may contact any regional
registry and the regional registry may either handle the request or
refer the request to an appropriate registry.
To facilitate hierarchical addressing, implemented using Classless
Inter-Domain Routing (CIDR), all other ISPs should request address
space directly from its upstream provider. ISPs only request address
space directly from regional registries if their immediate
requirement, when satisfied with a contiguous block allocation, has a
reasonable probability of being routable on the Internet, and they
meet one or more of the following conditions.
a) the ISP is directly connected to a major routing exchange
(for purposes of this document, a major routing exchange
is defined as a neutral layer 2 exchange point connecting
four or more unrelated ISPs.)
b) the ISP is multi-homed, that is, it has more than one
simultaneous connection to the global Internet and no
connection is favored over the other
Note that addresses issued directly from the IRs (non-provider
based), are the least likely to be routable across the Internet.
The following are the IP allocation guidelines for ISPs:
1. CIDR addresses are allocated to ISPs in blocks. It is
recommended that those blocks remain intact. Fragmentation of
CIDR blocks is discouraged. More specifically, ISPs are
encouraged to treat address assignments as loans for the
duration of the connectivity provision. At the termination
of the Internet connectivity contract, e.g., the customer
moves to another service provider, it is recommended the
customer return the network addresses currently in use and
renumber into the new provider's address space. The ISP
should allow sufficient time for the renumbering process to be
completed before the IP addresses are reused.
2. To ensure efficient implementation and use of Classless
Inter-Domain Routing (IDR), the Regional Registries issue
address space on appropriate "CIDR-supported" bit boundaries.
3. ISPs are required to utilize address space in an efficient
manner. To this end, ISPs should have documented
justification available for each assignment. The regional
registry may, at any time, ask for this information. If the
information is not available, future allocations may be impacted.
In extreme cases, existing loans may be impacted.
4. IP addresses are allocated to ISPs using a slow-start
procedure. New ISPs will receive a minimal amount based
on immediate requirement. Thereafter, allocated blocks may be
increased based on utilization verification supplied to the
regional registry. The parent registries are responsible for
determining appropriate initial and subsequent allocations.
Additional address allocations will provide enough address space
to enable the ISP to assign addresses for three months
without requesting additional address space from its parent
registry. Please note that projected customer base has little
impact on the address allocations made by the parent registries.
Initial allocation will not be based on any current or future
routing restrictions but on demonstrated requirements.
5. Due to the requirement to increase the utilization efficiency
of IPv4 address space, all assignments are made with the
assumption that sites make use of variable length subnet mask
(VLSM) and classless technologies within their network. Any
request for address space based on the use of classfull
assumptions will require a detailed justification. The use of
classfull technologies for the purposes of administrative
convenience is generally insupportable due to the limited
availability of free IPv4 address space.
6. Regional registries may set a maximum limit on assignment sizes
such that a second opinion of the regional registry is required.
7. Due to constraints on the available free pool of IPv4 address
space, the use of static IP address assignments (e.g., one
address per customer) for dial-up users is strongly discouraged.
While it is understood that the use of static addressing may
ease some aspects of administration, the current rate of
consumption of the remaining unassigned IPv4 address space does
not permit the assignment of addresses for administrative ease.
Organizations considering the use of static IP address assignment
are expected to investigate and implement dynamic assignment
technologies whenever possible.
2.2 Submission of Reassignment Information
It is imperative that reassignment information be submitted in a
prompt and efficient manner to facilitate database maintenance and
ensure database integrity. Therefore, assignment information must be
submitted to the regional registry immediately upon making the
assignment. The following reasons necessitate transmission of the
a) to provide operational staff with information on who is using
the network number and to provide a contact in case of
b) to ensure that a provider has exhausted a majority of its
current CIDR allocation, thereby justifying an additional
c) to assist in IP allocation studies.
Procedures for submitting the reassignment information will be
determined by each regional registry based on its unique
All sub-registries (ISPs, Local registries, etc.) must register with
their respective regional registry to receive information regarding
reassignment guidelines. No additional CIDR blocks will be allocated
by the regional registry or upstream providers until approximately
80% of all reassignment information has been submitted.
3. Assignment Framework
An assignment is the delegation of authority over a block of IP
addresses to an end enterprise. The end enterprise will use
addresses from an assignment internally only; it will not sub-
delegate those addresses. This section discusses some of the issues
involved in assignments and the framework behind the assignment of
In order for the Internet to scale using existing technologies, use
of regional registry services should be limited to the assignment of
IP addresses for organizations meeting one or more of the following
a) the organization has no intention of connecting to
the Internet-either now or in the future-but it still
requires a globally unique IP address. The organization
should consider using reserved addresses from RFC1918.
If it is determined this is not possible, they can be
issued unique (if not Internet routable) IP addresses.
b) the organization is multi-homed with no favored connection.
c) the organization's actual requirement for IP space is
very large, for example, the network prefix required to
cover the request is of length /18 or shorter.
All other requestors should contact its ISP for address space or
utilize the addresses reserved for non-connected networks described
in RFC1918 until an Internet connection is established. Note that
addresses issued directly from the IRs,(non-provider based), are the
least likely to be routable across the Internet.
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
25% immediate utilization rate
50% utilization rate within 1 year
The utilization rate above is to be used as a guideline, there may be
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
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
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 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
3.2 Network Engineering Plans
Before a registry makes an assignment, it must examine each address
space request in terms of the requesting organization's networking
plans. These plans should be documented, and the following
information should be included:
1. subnetting plans, including subnet masks and number of
hosts on each subnet for at least one year
2. a description of the network topology
3. a description of the network routing plans, including the
routing protocols to be used as well as any limitations.
The subnetting plans should include:
a) a tabular listing of all subnets on the network
b) its associated subnet masks
c) the estimated number of hosts
d) a brief descriptive remark regarding the subnet.
If subnetting is not being used, an explanation why it cannot be
implemented is required. Care must be taken to ensure that the host
and subnet estimates correspond to realistic requirements and are not
based on administrative convenience.
3.3 Previous Assignment History
To promote increased usage of address space, the registries will
require an accounting of address space previously assigned to the
enterprise, if any. In the context of address space allocation, an
"enterprise" consists of all divisions and/or subsidiaries falling
under a common parent organization. The previous assignment history
should include all network numbers assigned to the organization, plus
the network masks for those networks and the number of hosts on each
(sub-)network. Sufficient corroborating evidence should be provided
to allow the assigning registry to be confident that the network
descriptions provided are accurate. Routing table efficiency will be
taken into account by the regional registries and each request will
be handled on a case by case basis.
3.4 Network Deployment Plans
In order to assign an appropriate amount of space in the required
time frame, a registry may request deployment plans for a network.
Deployment plans should include the number of hosts to be deployed
per time period, expected network growth during that time period, and
changes in the network topology that describe the growth.
3.5 Organization Information
A registry may request that an organization furnish a published
description verifying that the organization is what it claims to be.
This information can consist of brochures, documents of
incorporation, or similar published material.
3.6 Expected Utilization Rate
As stated in the foregoing text, one of the key factors in
determining how much address space is appropriate for an organization
is the expected utilization rate of the network. The expected
utilization rate is the number of hosts connected to the network
divided by the total number of hosts possible on the network. In
addition, the estimated number of hosts should be projected over a
reasonable time frame, i.e., one in which the requesting enterprise
has a high level of confidence. The minimal utilization rate is set
by the IANA and may be changed at any time. New utilization rates
may be enforced by the regional registries prior to updating the
4. Operational Guidelines For Registries
1. Regional Registries provide registration services as its
primary function. Therefore, regional registries may charge some
fee for services rendered, generally in relation to the cost of
providing those services.
2. Regardless of the source of its address space, sub-registries
(Local IRs, ISPs, etc.) must adhere to the guidelines of its
regional registry. In turn, it must also ensure that its
customers follow those guidelines.
3. To maximize the effective use of address space, IP addresses need
to be assigned/allocated in classless blocks. With this in mind,
assignments will not be made in Class Cs or Bs but by prefix
length. Consequently, an organization that would have been
assigned a Class B in the past will now be assigned a /16 prefix,
regardless of the actual address class.
4. All IP address requests are subject to audit and verification
by any means deemed appropriate by the regional registry.
If any assignment is found to be based on false information,
the registry may invalidate the request and return the
assigned addresses back to the pool of free addresses for
5. Due to technical and implementation constraints on the Internet
routing system and the possibility of routing overload, major
transit providers may need to impose certain restrictions to
reduce the number of globally advertised routes. This may
include setting limits on the size of CIDR prefixes added to
the routing tables, filtering of non-aggregated routes, etc.
Therefore, addresses obtained directly from regional registry
(provider-independent, also known as portable) are not
guaranteed routable on the Internet.
6. Information provided to request address space is often considered
sensitive by the requesting organization. The assigning
registry must treat as confidential any and all information
that the requesting organization specifically indicates as
sensitive. When a requesting organization does not have
assurance of privacy, the parent of the assigning registry may
be required to do the assignment. In such cases, the parent
registry will provide the assigning registry with information
regarding the appropriate amount of address space to allocate.
7. The transfer of IP addresses from one party to another must be
approved by the regional registries. The party trying to obtain
the IP address must meet the same criteria as if they were
requesting an IP address directly from the IR.
5. In-ADDR.ARPA Domain Maintenance
The regional registries will be responsible for maintaining IN-
ADDR.ARPA records only on the parent blocks of IP addresses issued
directly to the ISPs or those CIDR blocks of less than /16. Local
IRs/ISPs with a prefix length of /16 or shorter will be responsible
for maintaining all IN-ADDR.ARPA resource records for its customers.
IN-ADDR.ARPA resource records for networks not associated with a
specific provider will continue to be maintained by the regional
6. Right to Appeal
If an organization feels that the registry that assigned its address
has not performed its task in the requisite manner, the organization
has the right of appeal to the parent registry.
In such cases, the assigning registry shall make available all
relevant documentation to the parent registry, and the decision of
the parent registry shall be considered final (barring additional
appeals to the parent registry's parent). If necessary, after
exhausting all other avenues, the appeal may be forwarded to IANA for
a final decision. Each registry must, as part of their policy,
document and specify how to appeal a registry assignment decision.
[RFC 1519] Fuller, V., Li, T., Yu, J., and K. Varadhan,
"Classless Inter- Domain Routing (CIDR): an Address
Assignment and Aggregation Strategy", September 1993.
[RFC 1518] Rekhter, Y., and T. Li, "An Architecture for IP
Address Allocation with CIDR", September 1993.
[RFC 1918] Rekhter, Y., Moskowitz, B., Karrenberg, D., and
G. de Groot, "Address Allocation for Private Internets",
[RFC 1814] Gerich, E., "Unique Addresses are Good", June 1995.
[RFC 1900] Carpenter, B., and Y. Rekhter, "Renumbering Needs Work",
8. Security Considerations
Security issues are not discussed in this memo.