ARIN Document for ISPs' Customers

The following draft document will be presented for discussion at ARIN's
upcoming meeting in San Francisco. Please take a few minutes to review it in
preparation for the CLEW meeting. This document is also attached in MSWord
format.

Barry Skeenes


Who Is ARIN?
What Do They Do?
What Are the Requirements that ISP Customers Must Meet?

Contents

1.    Introduction
2.    IP Addressing Review
3.    Internet Organization
4.    ARIN as Custodian
5.    ISPs as Agents of ARIN (LIRs)
6.    Reassignment Policy
7.    Early Registrations and IPv4 Address Reclamation
8.    IPv6 Addressing
9.    Renumbering
10.  Routing Tables and Address Aggregation
11.  Autonomous System (AS) Numbers

1.  Introduction

This document is intended to help ISPs educate their customers about ARIN's
IP
allocation and assignment policies and the restrictions that are required of
them. All downstream customers of ISPs are equally required to follow the
reassignment, justification, and utilization guidelines that their upstream
ISP must follow as described in policy documents posted on ARIN's website
and referenced herein. This creates a level playing field for receiving and
utilizing IP numbers and helps to ensure that addresses are not wasted by
providers reassigning space without restriction. IP space is a limited
public resource that must be conserved and allocated prudently.

2.  IP Addressing Review

IP addresses are the globally unique numbers that map domain names to
networks and end users. The Domain Name System (DNS) performs the
translation from names to numbers. Internet Protocol version 4 (IPv4) is the
IP addressing system in use today. It consists of a 32-bit string divided
into four groups of eight bits (octets).

Each IP address includes a network identity reference as well as a local
connection identifier. In earlier times, the total available IPv4 address
space, consisting of 4.29 billion addresses, was allocated following a
"classful" scheme which predefined address blocks as very large (Class A),
large (Class B), or small (Class C). In many cases these blocks contained
many more addresses than the receiving organization could utilize. This
contributed to the rapid depletion of IPv4 addresses.

The success of the Internet to serve as a commercial infrastructure
available to all entities required a more efficient mechanism. A new
"classless" process, referred to as Classless Inter-Domain Routing (CIDR),
was developed and is based on the IP numbering needs of ARIN's subscribers
and end users. While not totally efficient, it utilizes addresses much more
efficiently than the wasteful method of allocating predefined blocks.

Understanding IP Addressing: Everything You Ever Wanted to Know,
http://www.3com.com/nsc/501302.html, provides an excellent description of
the IP addressing system.

3.  Internet Organization

The global Internet registry system in place today is hierarchical in nature
and consists of the Internet Corporation for Assigned Names and Numbers
(ICANN), the Address Supporting Organization (ASO) of ICANN, three Regional
Internet Registries (RIRs), National Internet Registries (NIRs), Local
Internet Registries (LIRs), Internet Service Providers (ISPs), and end
users. ARIN's region consists of ICANN, the ASO, ARIN as the region's RIR,
two NIRs, commercial ISPs, and end user organizations.

ICANN maintains authority for all IP numbers globally and sets address
policy with input from the ASO (an ICANN organization made up of the three
RIRs), the RIRs, and the general community.

ARIN receives /8 blocks from ICANN to allocate, in appropriately sized
blocks, to the NIRs or qualified ISPs and end users in its region. ISPs and
NIRs in turn reassign space to their downstream customers, which could be
second- or third-tier providers, or end-user organizations.

4.  ARIN as Custodian

In the days when the Internet was expanding into a true global network, and
IPv4 was getting its start, conventional thinking suggested that IPv4 would
provide plenty of address space for many years to come. However, no one
could foresee the rapid growth that would occur, and it soon became apparent
that IPv4 resources would run out in the near term if conservation efforts
were not employed. Paramount to ARIN and the work of all the RIRs, is their
role in ensuring that service providers and user organizations effectively
utilize address space without unnecessary waste.

As of March 2001, it is estimated that nearly 60% of IPv4 space has been
allocated. Estimates vary as to how long the remaining IPv4 space will last,
but given the rapid development of emerging technologies and the importance
of Internet resources to the world and its economy, we must all be prudent
in how we handle this public resource.

5.  ISPs as Agents of ARIN

ARIN allocates IP addresses predominantly to large ISPs (known as ARIN
subscribers), and to large end-user organizations with a user base
sufficient to qualify for receiving addresses directly from ARIN. ISPs
reassign numbers to other ISPs and to their end-user customers. All
downstream customers are responsible for ensuring that their customers
adhere to ARIN's policies. This distributes responsibility among all those
involved in the allocation process and helps to ensure that the routing
infrastructure remains operational. Each should effectively utilize their
assigned space and that of their customers.

Specifically, ISPs and all their downstream customers should employ the use
of Variable Length Subnet Mask (VLSM) and CIDR. These methods provide the
means for reassigning addresses in the size block needed by the respective
organization or user.

6.  Reassignment Policy

When requesting additional allocations, ISPs must show justification for the
request and must demonstrate their need by submitting reassignment
information using ARIN's Shared WHOIS Project (SWIP) or a RWHOIS server.
With this data in place, ARIN can readily review an ISP's address
utilization to determine whether the provider satisfies the requirements.
Inefficient use of IP space will hinder an organization's efforts to receive
additional addresses in the future and may render it unable to meet its
long-term goals and requirements.

Each ARIN subscriber is responsible for ensuring that their customers
provide reassignment information and identify the data by referencing the
provider's Maintainer ID, an identifier assigned the provider upon their
first allocation from ARIN.

7.  Early Registrations and IPv4 Address Reclamation

"Early registrations" refers to the large blocks of addresses that were
allocated before ARIN was organized. These blocks were allocated using a
classful methodology (see Section 1); and, because these blocks were often
much larger than an organization needed, ARIN and the overall Internet
community are now actively interested in reclaiming the early registrations
that are unused or underutilized. ARIN encourages organizations to return
the portions that are not being utilized, or to trade them for more
appropriately sized address blocks.

ARIN has been holding public discussions about this matter and seeks a
satisfactory resolution for all concerned parties. This would go a long way
toward meeting ARIN's mandate of ensuring equal access by all through the
prudent use of all IPv4 address space.

8.  IPv6 Addressing

The standards community has developed a next-generation IP system which has
greatly expanded the amount of address space available for the future.
However, inefficient address assignments and growth of the routing tables
remain serious potential threats to the scalability of the Internet, and
thus its operability.

Named IPv6, this system employs the use of 128-bit numbers divided into
Top-Level Aggregation Identifiers (TLAs), Mid-Level Aggregation Identifiers
(MLAs), and Site-Level Aggregation Identifiers (SLAs). The first TLA prefix
is divided into sub-TLAs representing the initial /35 blocks that are
currently being allocated.

The RIRs began making IPv6 allocations in mid-1999, but it is unclear when
IPv6 will become production ready. ARIN and the Internet community are
proceeding in a conservative fashion to maintain routing table size and to
ensure that the historical underestimation of IPv4 is not repeated with
IPv6.

9.  Renumbering

IP addresses are allocated to ISPs in contiguous blocks, which should remain
intact. Understandably, ISP customers prefer their block of IP addresses to
be provider-independent (portable) in order to avoid having to renumber into
a new reassignment should they change providers. However, ISPs are
encouraged to require their customers to return the address space if they
change ISPs. The customer would then renumber into the new provider's
address space.

If this practice were not followed, a situation of serious concern for the
operability of the Internet today would result: routing table overload (see
Section 10).

10.  Routing Table and Address Aggregation

Routing table entries specify how traffic is routed to individual network
addresses across the Internet. IP address blocks allocated to first-tier or
upstream ISPs must remain contiguous so that addresses can be aggregated. If
address and route aggregation are employed efficiently, a single routing
table entry is capable of representing thousands of addresses, minimizing
the number of routing entries in the routing table. This is important in
that too many entries would cause routing table overload, potentially
rendering portions of the Internet inaccessible.

11.  Autonomous System (AS) Numbers

AS Numbers are globally unique numbers used to enable ASes to exchange
routing information with other ASes. An AS is a connected group of IP
networks that adheres to a single routing policy that differs from its
border gateway peers. Requests for AS Numbers must be accompanied by
verification that the requesting organization is multi-homed and its routing
policy is unique. Sites that do not require a unique AS Number should use
the AS Numbers reserved by the IANA (64512 through 65535) for private system
use.
Because AS Numbers are rapidly depleting, a new system is currently under
discussion.



Note: As this document may be updated periodically, please check ARIN's
website to verify that you have the latest revision.
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