The name invalid is reserved by the

Internet Engineering Task Force The Internet Engineering Task Force (IETF) is a standards organization for the Internet and is responsible for the technical standards that make up the Internet protocol suite (TCP/IP). It has no formal membership roster or requirements and ...

(IETF) in RFC 2606 (June 1999) as a domain name that may not be installed as a

top-level domain A top-level domain (TLD) is one of the domains at the highest level in the hierarchical Domain Name System of the Internet after the root domain. The top-level domain names are installed in the root zone of the name space. For all domains in ...

in the

Domain Name System The Domain Name System (DNS) is a hierarchical and distributed naming system for computers, services, and other resources in the Internet or other Internet Protocol (IP) networks. It associates various information with domain names assigned ...

(DNS) of the

Internet The Internet (or internet) is the global system of interconnected computer networks that uses the Internet protocol suite (TCP/IP) to communicate between networks and devices. It is a '' network of networks'' that consists of private, p ...

.RFC 2606 (BCP 32), ''Reserved Top Level DNS Names'', D. Eastlake, A. Panitz, The Internet Society (June 1999)

Reserved DNS names

In 1999, the

reserved the DNS labels , , , and so that they may not be installed into the root zone of the Domain Name System. The reasons for reservation of these top-level domain names is to reduce the likelihood of conflict and confusion.RFC 2606 (BCP 32), ''Reserved Top Level DNS Names'', D. Eastlake, A. Panitz, The Internet Society (June 1999) This allows the use of these names for either documentation purposes or in local testing scenarios.

Purpose

This top-level domain is sometimes used as a pseudo domain name in

Uniform Resource Identifier A Uniform Resource Identifier (URI) is a unique sequence of characters that identifies a logical or physical resource used by web technologies. URIs may be used to identify anything, including real-world objects, such as people and places, conc ...

s (URIs) to convey either an error condition or in use of privacy protection. A notable instance of this usage is in the

Session Initiation Protocol The Session Initiation Protocol (SIP) is a signaling protocol used for initiating, maintaining, and terminating communication sessions that include voice, video and messaging applications. SIP is used in Internet telephony, in private IP telep ...

(SIP) where the domain name in a SIP URI indicates hiding of a caller's identity.RFC 3325, ''Private Extensions to the Session Initiation Protocol'', C. Jennings, J. Peterson, M. Watson, The Internet Society (November 2002)

References

{{DEFAULTSORT:INVALID Top-level domains Internet properties established in 1999 Computer-related introductions in 1999 ja:トップレベルドメイン#特殊用途 sv:Toppdomän#Generiska toppdomäner