Which of the following network devices operate at the network layer of the OSI model? Each
correct answer represents a complete solution. Choose all that apply.

A.
Router

B.
Bridge

C.
Repeater

D.
Gateway

Explanation:

A router is a device that routes data packets between computers in different networks. It is used to
connect multiple networks, and it determines the path to be taken by each data packet to its
destination computer. A router maintains a routing table of the available routes and their
conditions. By using this information, along with distance and cost algorithms, the router
determines the best path to be taken by the data packets to the destination computer. A router can
connect dissimilar networks, such as Ethernet, FDDI, and Token Ring, and route data packets
among them. Routers operate at the network layer (layer 3) of the Open Systems Interconnection
(OSI) model.
A gateway is a network point that acts as an entrance to another network. On the Internet, a node
or stopping point can be either a gateway node or a host (end-point) node. Both the computers of
Internet users and the computers that serve pages to users are host nodes. The computers that
control traffic within a company’s network or at a local Internet service provider (ISP) are gateway
nodes. In the network for an enterprise, a computer server acting as a gateway node is often also
acting as a proxy server and a firewall server. A gateway is often associated with both a router,
which knows where to direct a given packet of data that arrives at the gateway, and a switch,
which furnishes the actual path in and out of the gateway for a given packet. Most of the gateways
operate at the application layer, but can operate at the network or session layer of the OSI model.
Answer option C is incorrect. A repeater operates only at the physical layer of the OSI model.
Answer option B is incorrect. A bridge operates at the data link layer of the OSI model.