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IPv4 Policies

These pages and the links below are presented in the format of ARIN policy that was effective through October 14, 2004. This method of formatting was superseded by the format in the Number Resource Policy Manual (NRPM), which was published on October 15, 2004.

ISP Initial Address Space Request Policy

ARIN allocates blocks of IP addresses to Internet Service Providers (ISPs) for the purpose of reassigning that space to their customers. ARIN takes guidance from allocation policies and procedures set forth in RFC 2050. A distinction is made between address allocation and address assignment, i.e., ISPs are "allocated" address space as described herein, while end-users are "assigned" address space.

Provider independent (portable) addresses issued directly from ARIN or other Regional Registries are not guaranteed to be globally routable. Therefore, ISPs should consider the following order of priority when requesting IP address space:

  1. Request IP address space from upstream provider

  2. Request IP address space from provider's provider

  3. Request IP address space from ARIN (not guaranteed to be globally routable)

Determination of IP address space allocation size is the responsibility of ARIN. In an effort to ensure that Classless Inter-Domain Routing (CIDR) is implemented and utilized as efficiently as possible, ARIN issues blocks of addresses on appropriate "CIDR-supported" bit boundaries.

In general, ARIN allocates IP address prefixes no longer than /20 to ISPs. If allocations smaller than /20 are needed, ISPs should request address space from their upstream provider. For multi-homed ISPs, ARIN allocates IP address prefixes no longer than /22. If allocations smaller than /22 are needed, multi-homed ISPs should request address space from their upstream provider. [Policy 2002-3] [Designation of a /13 as the maximum allocation size was removed by Policy 2003-14: Remove /13 Maximum Allocation]

Because the number of available IP addresses on the Internet is limited, many factors must be considered in the determination of address space allocations. Therefore, IP address space is allocated to ISPs using a slow-start model. Allocations are based on justified need, not solely on a predicted customer base.

Requirements for Requesting Initial Address Space

Utilization rate of address space is a key factor, among others, in determining address allocation. IP address allocations are valid as long as the utilization and other relevant criteria continue to be met, and the yearly fee is submitted. ARIN may invalidate any IP allocation if it determines that the requirement for the address space no longer exists. In the event of address space recall, ARIN will make every reasonable effort to inform the organization that the addresses are being returned to the free pool of IPv4 address space.

Organizations that do not meet the multi-homed requirements described below must satisfy the following requirements:

1. The efficient utilization of an entire previously allocated /20 from their upstream ISP. This /20 allocation may have been provided by an ISP's upstream provider(s), and does not have to be contiguous address space. The organization must meet the requirement of efficient use of 16 /24s. For example, if an organization holds a smaller allocation, such as 12 /24s, from its upstream provider, the organization would not meet the minimum utilization requirements of a /20.

2. Demonstrate efficient use of IP address space allocations by providing appropriate documentation, including assignment histories, showing their efficient use. ISPs must provide reassignment information on the entire previously allocated block(s) via SWIP or RWhois server for /29 or larger blocks. For blocks smaller than /29 and for internal space, ISPs should provide utilization data using the table format described earlier.

This information must be visible via WHOIS prior to submitting a request for a new allocation. For further information on reassigning IP address space, please see RFC 2050.

To maintain the privacy of their residential customers, an organization with downstream residential customers may substitute that organization's name for the customer's name, e.g. 'Private Customer - XYZ Network', and the customer's street address may read 'Private Residence'. Each private downstream residential reassignment must have accurate upstream Abuse and Technical POCs visible on the WHOIS record for that block. [Policy 2003-3]

3. Provide detailed information showing specifically how a /20 will be utilized within three months.

4. When an ISP submits a request for IP address space to be used for IP-based web hosting, it will supply (for informational purposes only) its technical justification for this practice. ARIN will analyze this data continuously, evaluating the need for future policy change.

ISPs receiving a new /20 may wish to renumber out of their previously allocated space. In this case, an ISP must use the new /20 to renumber out of that previously allocated block of address space and must return the space to its upstream provider.

If an ISP has an immediate need for address space, i.e., the need exists the day of the request, ARIN may issue a /20 if the organization, such as a new company, shows justification. However, these cases are exceptional.

Multi-homed Policy

An organization is multi-homed if it receives full-time connectivity from more than one ISP and has one or more routing prefixes announced by at least two of its upstream ISPs.

When prefixes are allocated which are longer than /20, they will be from a block reserved for that purpose. In order to receive an initial allocation from ARIN, multi-homed organizations must:

  • When requesting a /22, demonstrate the efficient utilization of a minimum contiguous or noncontiguous /23 (two /24s) from an upstream.

  • When requesting a /21, demonstrate the efficient utilization of a minimum contiguous or noncontiguous /22 (four /24s) from an upstream.

  • When requesting a /20, demonstrate the efficient utilization of a minimum contiguous or noncontiguous /21 (eight /24s) from an upstream.

  • Provide reassignment information for /29 and shorter prefix lengths using the Shared WHOIS Project (SWIP) or by providing the same information fields in an RWhois server. If additional address space is later requested, this information must be available at the time of the request. Utilization for blocks smaller than /29 can be documented using the following format:

    City Which IP Addresses Assigned No. of Ports No. of Dial-up Clients
    City Which IP Addresses Assigned No. of Internal Machines Purpose
    Which IP Addresses Assigned List URLs for Websites
  • Provide detailed information showing that the requested IP address space will be utilized within three months.

  • Agree that the newly requested IP address space will be used to renumber out of the current addresses which will be returned to their upstream provider(s).

To maintain the privacy of their residential customers, an organization with downstream residential customers may substitute that organization's name for the customer's name, e.g. 'Private Customer - XYZ Network', and the customer's street address may read 'Private Residence'. Each private downstream residential reassignment must have accurate upstream Abuse and Technical POCs visible on the WHOIS record for that block. [Policy 2003-3]

To receive additional address space following the initial allocation, multi-homed organizations must have returned the original IP address space to its provider in its entirety and must provide justification for a new allocation as described above in the section titled Requirements for Requesting Initial Address Space.

Web Hosting Policy

When an ISP submits a request for IP address space to be used for IP-based web hosting, it will supply (for informational purposes only) its technical justification for this practice. ARIN will analyze this data continuously, evaluating the need for future policy change.

Adopted by Board of Trustees July 27, 2001

Immediate Need Policy

If an ISP has an immediate need for address space, i.e., the need exists the day of the request, ARIN may issue a /20 if the organization, such as a new company, shows justification. However, these cases are exceptional.

Cable Address Space Policy

In most cases, ISPs that have residential cable subscribers assign address space to their cable infrastructure to which their customers connect rather than to individual subscribers. This assignment information regarding each market area holding an address block should be entered via the SWIP template (or by using RWhois) with the network name used to identify each market area. Initial allocations are based on total number of homes that could purchase the service in a given market area.

Using SWIP or RWhois, cable ISPs must show that they have reassigned at least 80% of their current address space, with a 50 to 80% utilization rate, in order to request additional addresses.

Each assignment to a specific end-user (if holding /29 and larger blocks) requires the submission of a SWIP template or use of an RWhois server. Requesters will also be asked to provide detailed plans for use of the newly requested space.

Maintaining IN-ADDRs

All ISPs receiving one or more distinct /16 CIDR blocks of IP addresses from ARIN will be responsible for maintaining all IN-ADDR.ARPA domain records for their respective customers. For blocks smaller than /16, and for the segment of larger blocks which start or end with a CIDR prefix longer than /16, ARIN can maintain IN-ADDRs through the use of the SWIP (Reallocate and Reassign) templates or the Netmod template for /24 and shorter prefixes.

Reassigning Address Space to Customers

ISPs are required to apply a utilization efficiency criterion in providing address space to their customers. To this end, ISPs should have documented justification available for each reassignment. ARIN may request this justification at any time. If justification is not provided, future receipt of allocations may be impacted. In extreme cases, existing allocations may be affected.

To increase utilization efficiency of IPv4 address space, ISPs reassigning IP address space to their customers should require their customers to use variable length subnet mask (VLSM) and classless technologies (CIDR) within their networks.

IP addresses are allocated to ISPs in contiguous blocks, which should remain intact. Fragmentation of blocks is discouraged. To avoid fragmentation, ISPs are encouraged to require their customers to return address space if they change ISPs. Therefore, if a customer moves to another service provider or otherwise terminates a contract with an ISP, it is recommended that the customer return the network addresses to the ISP and renumber into the new provider's address space. The original ISP should allow sufficient time for the renumbering process to be completed before requiring the address space to be returned.

All extra-large ISPs making reassignments of a /18 or greater to a customer must first have these reassignments reviewed and approved by ARIN. Likewise, all small to large ISPs making customer reassignments of a /19 or greater must first seek ARIN's approval. The following information should accompany the template:

  1. Network engineering plans, including subnets, host counts, and hosts per subnet, with projected utilization rates and associated confidence levels of those projections for one and two years

  2. Deployment schedule for the network, including major milestones for each subnet

  3. Network topology diagrams

ISP Additional Requests

ISPs must have efficiently utilized all previous allocations, and at least 80% of their most recent allocation in order to receive additional space. This includes all space reassigned to their customers.

To receive additional address space following the initial allocation, multi-homed organizations must have returned the original IP address space to its provider in its entirety and must provide justification for a new allocation as described above in the section titled Requirements for Requesting Initial Address Space.

Any time an ISP receives a new block of address space, reassignment information should be submitted within 7 days of issuance of the new space. This information is used to demonstrate that the address space received is being efficiently utilized. Also, it will be reviewed to determine an ISP's and its downstream customers' utilization effectiveness if and when additional space is requested in the future.

Requesters must satisfy the following requirements for ARIN to determine whether allocated space is being used efficiently:

  1. Provide utilization information via SWIP or RWhois for all /29 and shorter prefix lengths. SWIP and RWhois reassignments should show each client's organizational information. The format below should be used to provide the required information for utilization of blocks smaller than /29 and for describing internal networks.

    City Which IP Addresses Assigned No. of Ports No. of Dial-up Clients
    City Which IP Addresses Assigned No. of Internal Machines Purpose
    Which IP Addresses Assigned List URLs for Websites

    The reassignment information section of the ARIN ISP Network Request Template should be completed for all address blocks that have been allocated to your organization. In the template, line 1b. Assigned: information will be verified via SWIP/RWhois and 1c. Reserved: should be used to indicate internal network information. Please note that until your prior utilization is verified to meet the 80% requirement, ARIN can neither process nor approve a request for additional addresses.

  2. Demonstrate the effective use of the following guidelines in reassigning space to customers:

    • Issue prefix lengths longer than /24, wherever feasible

    • Obtain prior approval from ARIN for any /18 or shorter (for extra-large ISPs)

    • Obtain prior approval from ARIN for any /19 or shorter (for small-to-large ISPs)

  3. Require your downstream customers to adhere to the following criteria:

    • Reassignment information for prior allocations must show that each customer meets the 80% utilization criteria and must be available via SWIP/RWhois prior to your issuing them additional space. Note: To maintain the privacy of residential customers, the person's street address and phone number will not be provided.

    • Customers must follow ARIN guidelines for ISPs

    • Web host customers should report usage data in a form similar to the chart shown above

  1. Return prior address space designated for return as agreed.

  2. Provide detailed information showing that the address space will be utilized within three months. Determination of the appropriate allocation to be issued is based on efficient utilization of space within this three-month time frame. When completing Section 7 of the ARIN ISP Address Request Template, please keep this in mind.

  3. After a subscriber has been a member of ARIN for one year they may choose to request a six-month supply of IP addresses. [Policy 2003-13: Six-Month Supply of IP Addresses]

When an ISP submits a request for IP address space to be used for IP-based web hosting, it will supply (for informational purposes only) its technical justification for this practice. ARIN will analyze this data continuously, evaluating the need for future policy change.

ISPs requesting additional address space from ARIN beyond their initial allocation should follow the guidelines described in the ARIN ISP Guidelines for Requesting Additional IP Address Space.

End-user Assignments

In assigning IP address space to end-users, ARIN takes guidance from assignment policies and procedures set forth in RFC 2050. These guidelines were developed to meet the needs of the larger Internet community in conserving scarce IPv4 address space and allowing continued use of existing Internet routing technologies.

ARIN assigns blocks of IP addresses to end-users who request address space for their internal use in running their own networks, but not for sub-delegation of those addresses outside their organization. An end-user is an organization receiving assignments of IP addresses exclusively for use in its operational networks. End-users must meet the requirements described in these guidelines for justifying the assignment of an address block.

In general, the minimum block of IP address space assigned by ARIN to end-users is a /20. If assignments smaller than /20 are needed, end-users should contact their upstream provider. For multi-homed end-users, the minimum block of IP address space assigned is a /22. If assignments smaller than a /22 are needed, multi-homed end-users should contact their upstream providers. When prefixes are assigned which are longer than /20, they will be from a block reserved for that purpose. [Policy 2002-3]

Utilization rate of address space is a key factor in justifying a new assignment of IP address space. Requesters must show exactly how previous address assignments have been utilized and must provide appropriate details to verify their one-year growth projection. The basic criteria that must be met are:

  • A 25% immediate utilization rate, and

  • A 50% utilization rate within one year.

A greater utilization rate may be required based on individual network requirements. Please refer to RFC 2050 for more information on utilization guidelines.

End-users may qualify for address space under other policies such as Immediate need or Micro-allocation.

Non-connected Networks

End-users not currently connected to an ISP and/or plan not to be connected to the Internet are encouraged to use private IP numbers reserved for non-connected networks (see RFC 1918).

Micro-allocations (Policy 2001-3)

Note: This policy makes obsolete the former micro-allocation policy.

ARIN will make micro-allocations to critical infrastructure providers of the Internet, including public exchange points, core DNS service providers (e.g. ICANN-sanctioned root, gTLD, and ccTLD operators) as well as the RIRs and IANA. These allocations will be no longer than a /24 using IPv4 or a /48 using IPv6. Multiple allocations may be granted in certain situations.

Exchange point allocations MUST be allocated from specific blocks reserved only for this purpose. All other micro-allocations WILL be allocated out of other blocks reserved for micro-allocation purposes. ARIN will make a list of these blocks publicly available.

Exchange point operators must provide justification for the allocation, including: connection policy, location, other participants (minimum of two total), ASN, and contact information. ISPs and other organizations receiving these micro-allocations will be charged under the ISP fee schedule, while end-users will be charged under the fee schedule for end-users. This policy does not preclude exchange point operators from requesting address space under other policies.

Annual Renewal Policy

An annual fee for registered space is due by the anniversary date of the ISP's first allocation from ARIN. ISPs should take care to ensure that their annual renewal payment is made by their anniversary due date in accordance with the Registration Services Agreement. If not paid by the anniversary date, the address space may be revoked. Please review the Annual Renewal/Maintenance Fees Page for more details.

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