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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 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 startup by means of the Dynamic Host Configuration Protocol (DHCP), or by stateless address autoconfiguration methods.
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.
Origin of the concept
In operating systems, the term terminal host traditionally denotes a time-sharing computer or multi-user 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. 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..."
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 as they were not connected to any IP-based network, and were not assigned IP addresses.
Servers and nodes
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.
Every network host is a network node, but not every network node is a host. Network devices such as modems, hubs and network switches are not necessarily assigned network addresses (except sometimes for administrative purposes), and consequently may not be considered to be network hosts. Devices such as network printers and hardware routers have addresses, but since they are not general-purpose computers, they are sometimes not considered to be hosts.