How to Request an ASN from ARIN

By Jennifer Bly - Public Affairs Specialist, ARIN

By The Registration Services Department, ARIN

Autonomous System Number ASNThe ARIN Registration Services Department assists many organizations in obtaining Autonomous System Numbers (ASNs).  Last week you may have heard from the NRO that the global pool of available 2-byte ASNs is nearing depletion.  But let’s take a step back.  What is an ASN? Who needs one? Why? And how can you get one if you need one?

ASN: The Basics

ASN stands for Autonomous System Number.  It is a number that is used to define a group of routing prefixes that maintains a unique routing policy that differs from the routing policies of network border peers. ISPs use ASNs to control routing within their networks and to exchange routing information with other ISPs.  AS numbers (along with BGP) help routers and networks to identify where information comes from and where it should go outside a particular ISP’s network.  A public ASN is needed for an autonomous system to exchange routing information with two or more autonomous systems on the public Internet.

2-byte to 4-byte ASNs

There are two types of ASNs, 2-byte and 4-byte.  Similar to the case with IPv4 and IPv6 addresses, 4-byte ASNs were developed to meet the growing needs of a rapidly expanding Internet.   There are only 65,536 2-byte ASNs, and the 4-byte range provides an additional 4,294,967,296 AS numbers. Today only 496 2-byte ASNs remain globally. You can still request a 2-byte ASN for as long as we have them to distribute, but soon 4-byte ASNs will become the only option. You will find that the process to request 2-byte ASNs and 4-byte ASNs is the same, so follow along as we tell you how.

How to Get an ASN from ARIN

The Registration Services Department analyzes and processes many ASN requests each day.  We are happy to report that we are now seeing an uptake in 4-byte ASNs being implemented by our community.  In the past, we saw many people requesting 4-byte ASNs, only to exchange them for 2-byte ASNs the next week because their upstream provider told them they could not support 4-byte ASNs.  This situation seems to be rectifying itself and we are now regularly issuing many more 4-byte ASNs than 2-byte ASNs.

To qualify for an ASN from ARIN, you must have either a unique routing policy or a multihomed site.

If you are qualifying under the multihomed policy you will need to provide the exterior gateway protocol to be used, the IP addresses currently in use on your network, the AS number and name of each of your upstream providers and/or peers along with contractual verification of service with at least two of them.

If you are qualifying under the unique routing policy, you must demonstrate the AS’s routing policy will differ from the routing policies of its border peers.

No matter which policy you qualify under, if this is not your first time requesting an ASN, you will also need to show us how the network you are requesting an ASN for is autonomous from all existing ASes in your network as well.

If you meet the requirements, the next step is to apply for your number. That process works just like any other Internet number resource request.

  • Submit your request through ARIN Online
  • We will verify your request and issue a ticket for tracking purposes
  • Then we will review your request. We may have questions, and that communication will happen in your ticket.
  • If your request is approved, you will receive an invoice and a Registration Services Agreement.
  • Once we receive payment and a signed agreement, we will be able to complete the ASN assignment.

It’s that simple! If you have any questions along the way applying for your ASN, let us know.  You can email us at or call us at +1.703.227.0660. The RSD staff would be happy to help you.



Jennifer Bly

Public Affairs Specialist, ARIN