|TLD type||Reserved top-level domain|
|Status||Reserved to prevent conflict and confusion|
|Intended use||When necessary to show an address guaranteed to be invalid|
|Actual use||Session Initiation Protocol, for identity protection; address munging e.g. on Usenet|
The name invalid is reserved by the Internet Engineering Task Force (IETF) in RFC 2606 (June 1999) as a domain name that may not be installed as a top-level domain in the Domain Name System (DNS) of the Internet.
Reserved DNS names
The reasons for reservation of these top-level domain names is to reduce the likelihood of conflict and confusion. This allows the use of these names for either documentation purposes or in local testing scenarios.
This top-level domain is sometimes used as a pseudo domain name in Uniform Resource Identifiers (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 (SIP) where the domain name anonymous.invalid in a SIP URI indicates hiding of a caller's identity.
- RFC 2606 (BCP 32), Reserved Top Level DNS Names, D. Eastlake, A. Panitz, The Internet Society (June 1999)
- RFC 3325, Private Extensions to the Session Initiation Protocol, C. Jennings, J. Peterson, M. Watson, The Internet Society (November 2002)