The Secure Internet Protocol Router Network (SIPRNet) is "a system of interconnected computer networks used by the United States Department of Defense and the U.S. Department of State to transmit classified information (up to and including information classified SECRET) by packet switching over the TCP/IP protocols in a 'completely secure' environment". It also provides services such as hypertext document access and electronic mail. As such, SIPRNet is the DoD's classified version of the civilian Internet.
According to the U.S. Department of State Web Development Handbook, domain structure and naming conventions are the same as for the open internet, except for the addition of a Second-level domain, like, e.g., "sgov" between state and gov: openforum.state.sgov.gov. Files originating from SIPRNET are marked by a header tag "SIPDIS" (SIPrnet DIStribution). A corresponding Second-level domain smil.mil exists for DoD users.
According to the Pentagon, SIPRNet has approximately 4.2 million users. Access is also available to a "...small pool of trusted allies, including Australia, Canada, the United Kingdom and New Zealand..."
SIPRNet was one of the networks accessed by Bradley Manning, who allegedly leaked the video used in WikiLeaks' "Collateral Murder" release as well as the source of the US diplomatic cables published by WikiLeaks in November 2010.
See also 
- Classified website
- Joint Worldwide Intelligence Communications System (JWICS)
- Protected Distribution System
- Crisis Response Operations in NATO Operating Systems (CRONOS) is the NATO equivalent of SIPRNet
- "2005 Defense Base Closure and Realignment Commission Report: Fort Monmouth, New Jersey Recommendation # 5". U.S. Department of Defense. 28 December 2007. Retrieved 17 December 2010.
- "Secret Internet Protocol Router Network (SIPRNET)". Federation of American Scientists' Intelligence Resource Program. Retrieved 12 December 2010.
- "U.S. Department of State Foreign Affairs Handbook Volume 5 Handbook 8 - Web Development Handbook: 5 FAH-8 H-342.2 ClassNet Standards". U.S. Department of State. 29 September 2005. Retrieved 15 December 2010.
- "Siprnet: Where the leaked cables came from". BBC. 29 November 2010. Retrieved 19 December 2010.
- Grimes, John G. (14 April 2008). "Internet Domain Name Use and Approval". Department of Defense.
- Miller, Hayley (September 23 2011). "Security Clearances: 4.2 Million People Have Access To The Government's Classified Information". Huffington Post. Retrieved 23 August 2011.
- Field, Michael (2 December 2010). "NZ way down the WikiLeaks queue". Fairfax New Zealand. Retrieved 17 December 2010.
- Poulsen, Kevin; Zetter, Kim (6 June 2010). "U.S. Intelligence Analyst Arrested in Wikileaks Video Probe". Wired. Retrieved 15 June 2010.
- Leigh, David (28 November 2010). "US embassy cables leak sparks global diplomacy crisis". The Guardian. Retrieved 28 November 2010.