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A network host is a computer or other device connected to a computer network. A network host may offer information resources, services, and applications to users or other nodes on the network. A network host is a network node that is assigned a network layer host address.
Computers participating in networks that use the Internet Protocol Suite may also be called IP hosts. Specifically, computers participating in the Internet are called Internet hosts, sometimes Internet nodes. Internet hosts and other IP hosts have one or more IP addresses assigned to their network interfaces. The addresses are configured either manually by an administrator, automatically at start-up by means of the Dynamic Host Configuration Protocol (DHCP), or by stateless address autoconfiguration methods.
Every network host is a physical network node (i.e. a network device), but not every physical network node is a host. Network devices such as modems, hubs and network switches are not assigned host addresses (except sometimes for administrative purposes), and are consequently not considered to be network hosts. Devices such as network printers and hardware routers have IP addresses, but since they are not general-purpose computers, they are sometimes not considered to be hosts.
Network hosts that participate in applications that use the client-server model of computing, are classified as server or client systems. Network hosts may also function as nodes in peer-to-peer applications, in which all nodes share and consume resources in an equipotent manner.
Server vs. Host
All servers are hosts, but not all hosts are servers. Any device that has established a connection to a network qualifies as a host, whereas only hosts that accept connections from other devices (clients) qualify as servers.
Origin of the concept
In operating systems, the term terminal host traditionally denotes a multi-user computer or software providing services to computer terminals, or a computer that provides services to smaller or less capable devices, such as a mainframe computer serving teletype terminals or video terminals. Other examples are a telnet host (a telnet server) and an xhost (X Window client).
The term "Internet host" or just "host" is used in a number of Request for Comments (RFC) documents that define the Internet and its predecessor, the ARPANET. While the ARPANET was developed, computers connected to the network were typically mainframe computer systems that could be accessed from terminals connected via serial ports. Since these dumb terminals did not host software or perform computations themselves, they were not considered hosts. The terminals were connected to the terminal hosts through serial interfaces and perhaps circuit switched networks, but not connected to any IP based network, and were not assigned IP addresses. Today's IP hosts may, however, lack the ability to serve as terminal hosts.
RFC 871 defines a host as a general-purpose computer system connected to a communications network for "... the purpose of achieving resource sharing amongst the participating operating systems...".