Gateway: this device is placed at a network node and interfaces with another network that uses different protocols. It works on OSI layers 4 to 7.
Router: a specialized network device that determines the next network point to which it can forward a data packet towards the ultimate destination of the packet. Unlike a gateway, it cannot interface different protocols. It works on OSI layer 3.
Switch: a device that allocates traffic from one network segment to certain lines (intended destination(s)) which connect the segment to another network segment. Unlike a hub, a switch splits the network traffic and sends it to different destinations rather than to all systems on the network. It works on OSI layer 2.
Bridge: a device that connects multiple network segments along the data link layer. It works on OSI layer 2.
Hub: a device that connects multiple Ethernet segments, making them act as a single segment. When using a hub, every attached device shares the same broadcast domain and the same collision domain. Therefore, only one computer connected to the hub is able to transmit at a time. Depending on the network topology, the hub provides a basic level 1 OSI model connection among the network objects (workstations, servers, etc.). It provides bandwidth which is shared among all the objects, in contrast to switches, which provide a connection between individual nodes. It works on OSI layer 1.
Repeater: a device which amplifies or regenerates digital signals received while sending them from one part of a network into another. It works on OSI layer 1.
Hybrid network devices include:
Multilayer switch: a switch which, in addition to switching on OSI layer 2, provides functionality at higher protocol layers.
Protocol converter: a hardware device that converts between two different types of transmission, such as asynchronous and synchronous transmissions.
Bridge router (brouter): a device that combines router and bridge functionality and therefore works on OSI layers 2 and 3.
Hardware or software components which typically sit on the connection point of different networks (for example, between an internal network and an external network) include:
Proxy server: computer network service which allows clients to make indirect network connections to other network services.
Firewall: a piece of hardware or software put on the network to prevent some communications forbidden by the network policy.
Network address translator (NAT): network service (provided as hardware or as software) that converts internal to external network addresses and vice versa.
Other hardware devices used for establishing networks or dial-up connections include:
Multiplexer: a device that combines several electrical signals into a single signal.
Network interface controller (NIC): a device connecting a computer to a wire-based computer network.
Wireless network interface controller: a device connecting the attached computer to a radio-based computer network.
Modem: device that modulates an analog "carrier" signal (such as sound) to encode digital information, and that also demodulates such a carrier signal to decode the transmitted information. Used (for example) when a computer communicates with another computer over a telephone network.
ISDN terminal adapter (TA): a specialized gateway for ISDN.
Line driver: a device to increase transmission distance by amplifying the signal; used in base-band networks only.