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Table of Contents

Directory Services


Whois is a query and response protocol that is used for querying databases that store registered users or assignees of an Internet resource, such as IP addresses or domain names. ARIN's Whois service is a public resource that allows a user to retrieve information about IP number resources, organizations, and Points of Contact (POCs) registered with ARIN. It pulls this information directly from ARIN’s database, which contains IPv4 and IPv6 addresses, Autonomous System Numbers (ASNs), organizations, customer reassignments, and related POCs.

Note: ARIN will not collect any personal information for inclusion in its public Whois. The only information that is published in ARIN’s public Whois is organizational information associated with an Internet number resource, including POC records. The personal information you provide when creating your ARIN Online Profile is kept strictly confidential and is not displayed in your public Whois record.


ARIN’s Whois RESTful Web Service (Whois-RWS), much like the former Whois, is the directory service for accessing registration data contained within ARIN’s registration database. Whois-RWS can easily be integrated into command line scripts similar to Whois or RWhois, or it can be used with a web browser.

If you wish to use a Command-Line Interface (CLI) to access ARIN’s Whois Service, view our Quick Guide to ARIN’s Whois to learn more about how to customize your searches.

Registry Data Access Protocol (RDAP)

RDAP is a specification from the Internet Engineering Task Force (IETF) designed as a replacement for Whois data services for Domain Name Registries (DNRs) and Regional Internet Registries (RIRs). Unlike Whois, RDAP is an HTTP-based Representational State Transfer (REST)-style protocol with responses specified in JSON. Whois is a text based protocol, utilizing a specialized protocol and port. Whois defines no queries or responses, and as a result the interaction with DNRs and RIRs can vary significantly.

RDAP is specified in RFCs 7480, 7481, 7482, 7483, 7484, and 7485.

For more information, see the RDAP page.

Bulk Whois

Bulk Whois is a service by which ARIN provides access to a bulk copy of all objects in the ARIN Whois directory service to organizations that will use the data for Internet operational or technical research purposes that are described in the "Bulk Whois Terms of Use" (ToU).

Legacy Number Resources

ARIN provides certain registration services for legacy number resources without requiring legacy resource holders to enter into a registration services agreement or pay service fees.


The WhoWas service provides historical registration information for a given IP address or ASN. This service is available by request in the Downloads & Services section of ARIN Online. Requests are subject to approval and are covered by a Terms of Use agreement.

Number Resource Fraud Reporting

This fraud reporting process is to be used to notify ARIN of suspected Internet number resource fraud including the submission of falsified utilization or organization information, unauthorized changes to records within ARIN's database, hijacking of number resources in ARIN's database, or fraudulent transfers.

Whois Inaccuracy Reporting

This service is to be used to notify ARIN of inaccurate Whois records, including Point of Contact records (POCs), Organization Identifiers (Org IDs), Network records (NETs), and Autonomous System Numbers (ASNs) with outdated or erroneous organization or contact information. Upon receipt of the notification of inaccurate Whois data, ARIN staff will attempt to contact the organization associated with the inaccurate Whois entry and request updated information. To report a Whois Inaccuracy, select "Whois Inaccuracy Report" from the right menu on any page.

Resource Management Services

Provisioning and Maintenance of Registration Records (Reg-RWS)

In an effort to improve your ability to automate your interactions with ARIN’s database records, ARIN offers a RESTful interface for its provisioning systems. The Registration RESTful Web Service (Reg-RWS) provides an immediate response and enables more efficient and more complex interactions with ARIN systems than email templates.


ARIN Online customers can use DNS Security (DNSSEC) functionality by adding DS Records as part of DNS zone management. We encourage you to learn more about this service and the benefits of using DNSSEC.

Resource Public Key Infrastructure (RPKI)

ARIN Online users may now participate in RPKI: an opt-in service that allows users to certify their Internet number resources to help secure Internet routing. This initiative has been developed within the IETF's SIDR Working Group, with involvement from Regional Internet Registries (RIRs), and numerous Internet Service Providers (ISPs).

ARIN encourages members of the Internet community to certify their resources through RPKI. Internet routing today is vulnerable to hijacking and the provisioning/use of certificates is one of first steps required to make routing more secure.  Widespread RPKI adoption will help simplify IP address holder verification and routing decision-making throughout the ARIN region.

For more information about this crucial step in securing Internet routing, visit ARIN’s RPKI Home Page.

Cryptographic Authentication

ARIN Online and RESTful interfaces are the preferred methods for most transactions with ARIN. You are able to use HTTPS to be assured that your account information cannot be seen by others as you communicate with ARIN. Your ARIN Online account is protected because it is not readily known by the community via Whois (the legacy system identified the Points of Contacts who were able to make changes to the system).  As an additional protection, your ARIN Online accounts allows for you to link API keys to your RESTful calls. ARIN requires use of API keys for both RESTful and template transactions as of 19 March 2011.

In addition, in an effort to assure customers that email messages from ARIN are genuine, all messages sent from are authenticated by the ARIN PGP key signature.

CIDR Calculator

The CIDR Calculator allows you to convert an IP address range to CIDR notation or convert a CIDR prefix to an IP address range.

Reverse DNS Delegation Management

Reverse DNS is used to determine the domain name that is associated with a given IP address using the Domain Name System (DNS). The ARIN Online delegation management tools and ARIN's RESTful Provisioning system enable you to individually manage nameservers and to register Delegation Signer (DS) Resource Records for DNSSEC for each reverse delegation.

IPv4 Reverse DNS

All ISPs receiving one or more distinct /16 CIDR blocks of IPv4 addresses from ARIN will be responsible for maintaining all IN-ADDR.ARPA domain records for their respective customers. For blocks smaller than a /16, and for the segment of larger blocks smaller than a /16, ARIN can maintain IN-ADDRs.

IPv6 Reverse DNS

When ARIN delegates IPv6 address space to an organization, it also delegates the responsibility to manage the reverse lookup zone that corresponds to the allocated IPv6 address space. Each organization should properly manage its reverse lookup zone. When making an address assignment, the organization must delegate to an assignee organization, upon request, the responsibility to manage the reverse lookup zone that corresponds to the assigned address.

Routing Registry

The ARIN routing registry service allows network operators to submit, maintain, and retrieve router configuration information abstracted from the languages and syntaxes utilized by router configuration software. The Routing Registry page offers a detailed explanation of how to access and utilize this information to support your organization.

Operational Test and Evaluation environment (OT&E)

OT&E is an environment containing a copy of production-like data, refreshed monthly, that allows developers to experiment with ARIN interactions without affecting production data. See ARIN's OT&E page for more information.

Community Software Repository

As a service to the community, ARIN furnishes a software repository for tools that are related to ARIN's mission. These tools are furnished "as is" and maintained by members in the community.

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