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

For those who rely on existing scripts and clients, ARIN will continue to maintain services for the NICNAME/WHOIS protocol on TCP/43. This is achieved by using a proxy service to translate traditional ARIN Whois queries into Whois-RWS queries.

Note: What is REST? Representational State Transfer (REST) is a method of designing software systems that utilize Web technology to make defining, addressing, and exchanging data easier. RESTful systems usually utilize URLs that are sent using an Application Programming Interface (API).

How is ARIN using REST? ARIN provides a RESTful interface for:
- Whois queries (Whois-RWS)
- Provisioning and maintenance of Registration records (Reg-RWS)

Frequently Asked Questions

Will the NICNAME/WHOIS TCP port 43 service be turned off in the near future?
No. ARIN realizes that many long-term customers use this service. ARIN has no plans to retire it in the near future.
My parser broke. Why did you change the NICNAME/WHOIS port 43 output?
In July 2010, ARIN made minor changes to the output for clarity and better adherence to the existing Whois help documentation. Please read the Whois Differences documentation for a complete list of changes made to the NICNAME/WHOIS service in July 2010. In March 2011, ARIN made improvements to DNS that allow finer control of DNS delegations. This resulted in adding delegation queries to the Whois-RWS system, including port 43. ARIN recommends that you use the RESTful interface for a more stable and easily automated set of queries/results.

The results of my network, IP and CIDR queries no longer include nameserver information. What happened?

In March 2011, ARIN made improvements to DNS that allow finer control of DNS delegations. Delegation queries were added to the Whois-RWS system, including port 43. Nameservers and DNS DS record information now appear in delegation query results. Please reference the Whois-RWS API documentation for information on constructing these queries.
How do I use the ARIN Whois RESTful Web Service?
Several websites offer a lot of general documentation about RESTful services. Use your favorite search engine to find how-to documentation. For specifics about using ARIN’s RESTful service, please read our Whois-RWS Documentation.
My RESTful queries return hard-to-read xml. How do I make the output easier to understand?
Try submitting the query using the Firefox web browser; it will reformat that data and present it in a more readable form. Section 4 of the Whois-RWS documentation describes several other methods to reformat data outputs. .
Can I see the schemas for ARIN's Whois-RWS service?
Yes. The schemas are available on the ARIN website.
Should I change my code to parse the RESTful Interface instead of the NICNAME/WHOIS TCP port 43 service?
Absolutely. We encourage use of the new RESTful service for the purposes of programmatic consumption. ARIN plans to make more features available on the RESTful interface. The NICNAME/WHOIS service will remain accessible, but it may not support the enhanced features we intend to incorporate within Whois-RWS.
Where do I find clients that utilize Whois-RWS?
ARIN's web interface is an example client, as are most web browsers. ARIN has also developed a set of command line scripts called ARINcli, written in Ruby, that utilize both Whois-RWS and ARIN's Registration RESTful Web Service (Reg-RWS), and are available on Another Whois-RWS client has been developed by the community for use with Microsoft's .NET framework, and is available via a link on or on GitHub.
Can I use the web to search for ARIN registration information?
ARIN’s new web interface aims to be much friendlier than the legacy service. If you have any questions that are not answered on the web, please submit questions to so we can be sure to address them.
Is there an RFC that covers the RESTful interface you have developed?
Many ARIN staff members have written RFCs and put them into the standards track in the past. We hope to do the same for this service but standards can take two to three years to reach formal acceptance.  We are making Whois-RWS available now to provide a better directory service interface.
Is your code open source?
For the server, the code is specific to ARIN and matches our database closely.  We do not believe this code is very useful to the community.  If we do see demand, ARIN may develop or assist some motivated individual/organization to create a generic open source implementation.

On the client side, the RESTful interface has created a rich framework for application developers. We hope that people leverage this framework and contribute code. To that end, ARIN has created an open-source repository.
Do any other RIRs have a RESTful interface?
RIPE Labs is working on a RESTful interface for their directory services as well. They are doing the inverse of what ARIN is doing – they are creating a RESTful proxy to the legacy WHOIS/NICNAME port 43 service. ARIN, on the other hand, is creating a proxy from a RESTful service to the legacy WHOIS/NICNAME port 43 service. RIPE’s service is at
Is ARIN's RESTful provisioning service the same thing as ARIN's RESTful Whois service?
No. They are separate services that utilize the same web framework.  Expect to see more information on this alternative to submitting templates soon. Find out more about ARIN’s RESTful provisioning service and view its API documentation.
How do I find the parent/children networks of a network?
Please read section 4.4.3 of the Whois-RWS API documentation. The second example shows how to use the more or less operator. The less operator allows you to see the supernets (or parent networks) while the more operator allows you to see the subnets (or children networks) of a particular network.
Where do I find more information on RESTful web services in general?
Use your favorite search engine to find information on REST. Several sites do a good job describing RESTful web services, how to create them, and how to utilize them. A good book is O’Reilly’s RESTful Web Services by Richardson and Ruby.
How Can I Test Whois-RWS Interactions?
ARIN has implemented an Operational Test and Evaluation environment (OT&E) containing a copy of production-like data, refreshed monthly, that allows developers to experiment with ARIN interactions like Whois-RWS. For more information, see the OT&E page.

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