ARIN announces a pending change to Whois query behavior on port 43.

Prior to 25 June 2011, a query for an IP address in the ARIN region would return with that assignment/allocation within the ARIN region, and a query in the ARIN region for an IP address with no assignment/allocation would result in a “no match” response. On 25 June, a change was misapplied. The intent of this change was to return ARIN’s /8 for IP queries within ARIN’s region for which there is no assignment/allocation, a behavior meant to align ARIN’s Whois output with that of the other RIRs. However, this change introduced an unintended behavior of returning ARIN’s /8, in addition to the desired results, in responses where IP addresses had been assigned or allocated. This change in behavior has created some confusion. On 2 October, ARIN will reinstate the previous behavior for Whois IP queries so that results are returned the way they were before 25 June. ARIN has provided two examples of a Whois query for reference: one with ARIN's /8 returned in the result set hierarchy, and one without ARIN's /8 returned in the result set.
Whois-RWS behavior will not change as it was not affected by the configuration change made on 25 June.
We apologize for any confusion this has caused.

IP Address

An Internet Protocol address (IP address) is a numerical label assigned to each device (e.g., computer, printer) participating in a computer network that uses the Internet Protocol for communication.^[1] An IP address serves two principal functions: host or network interface identification and location addressing. Its role has been characterized as follows: "A name indicates what we seek. An address indicates where it is. A route indicates how to get there."^[2]


The designers of the Internet Protocol defined an IP address as a 32-bit number^[1] and this system, known as Internet Protocol Version 4 (IPv4), is still in use today. However, due to the enormous growth of the Internet and the predicted depletion of available addresses, a new addressing system (IPv6), using 128 bits for the address, was developed in 1995,^[3] standardized as RFC 2460 in 1998,^[4] and is being deployed worldwide since the mid-2000s.


IP addresses are binary numbers, but they are usually stored in text files and displayed in human-readable notations, such as 172.16.254.1 (for IPv4), and 2001:db8:0:1234:0:567:8:1 (for IPv6).
The Internet Assigned Numbers Authority (IANA) manages the IP address space allocations globally and delegates five regional Internet registries (RIRs) to allocate IP address blocks to local Internet registries (Internet service providers) and other entities.