Extranet
Extranet is a network or internetwork, is limited to a single organization or entity, but also has limited connections to the networks of one or more other usually, but not necessarily, trusted organizations or entities (eg customers of the company may be provides access to a portion of its intranet creating in this way an extranet, while customers can not be regarded as “trust” in terms of security). Technically, an extranet can be categorized as a box, MAN, WAN, or other type of network, although by definition an extranet existence of a local network, it at least one network connection to the outside world.
Internet
Internet is a global interconnection of government, academic, public and private networks based on network technology of Internet Protocol Suite. It is the successor of the Advanced Research Projects Agency Network (ARPANET), DARPA developed by the Board of the Ministry of Defense. The Internet is the communications backbone on which the World Wide Web (WWW). In the “Internet” is usually written with a capital ‘m’ as first name, for historical reasons and different from other general Internetworks.
Participants use the Internet for a variety of methods to several documented and often standardized, protocols compatible with the Internet Protocol Suite and addressing system (IP addresses), managed by the Internet Assigned numbers Authority and address registries. Service providers and large enterprises to exchange information about the accessibility of their address spaces across the border Gateway Protocol (BGP), creating a global network of redundant routes of transmission.
Computer-network 