2 Network Devices

This chapter introduces computer networks as systems that connect devices to share resources. It clarifies key terms: nodes are any devices on the network (including end hosts and infrastructure), and resources are the data and services exchanged between them. It also distinguishes Local Area Networks (LANs), which cover limited geographic areas like offices, from Wide Area Networks (WANs), which connect locations over large distances. The overall aim is to recognize common network devices and understand, at a high level, the roles they play in enabling communication.

The client–server model is presented as the foundation of how resources are shared: clients request services, and servers provide them. These are roles, not specific hardware types, and a single device can act as both depending on context. To scale beyond simple point-to-point connections, networks rely on infrastructure devices. Switches are highlighted as the core of a LAN, providing many physical ports to interconnect end hosts so they can communicate with one another within the same local network, without themselves being the destination of user traffic and without providing connectivity to external networks.

Routers sit at the edge of LANs to connect them to other networks, including the Internet and WANs, enabling communication between distinct networks. The chapter explains that consumer “wireless routers” commonly bundle multiple functions—router, switch, wireless access point, and firewall—suiting small office/home office environments, whereas enterprises typically separate these roles across dedicated devices. Firewalls add a layer of protection by inspecting inbound and outbound traffic and enforcing rules to allow or block it; the focus here is on network firewalls (hardware appliances), with a brief contrast to host-based firewalls on individual PCs. While firewalls are covered at a basic level, the primary emphasis for exam preparation remains on switches and routers.

An enterprise network connecting multiple offices together over the Internet

Icons representing a desktop computer and a file server. Icons like these are commonly used in network diagrams to represent clients and servers

Two desktop PCs sharing a file. The PC on the left is functioning as a client, and the PC on the right is functioning as a server

Three end hosts connected to a switch

Two LANs connected to the Internet via a router at the edge of each LAN.

A firewall between each LAN and the Internet secures the network. Network communications between the two LANs are allowed, but malicious traffic from an attacker is denied.

• A Local Area Network (LAN) is a group of interconnected devices in a limited area, such as an office.
• A Wide Area Network (WAN) is a network that extends over a large geographical area, such as between cities.
• A computer network is a telecommunications network which allows nodes to share resources.
• A node is any device that connects to a network: a personal computer, an iPhone, a router, etc.
• A resource is anything that is being shared over a network, such as a web page.
• Various types of network devices are used to facilitate network communications.
• Clients and servers are defined by their functions in relation to each other: clients access services provided by servers, and servers provide services for clients. Most types of devices can be both a client and a server.
• Switches provide connectivity between devices in a LAN. They typically have many ports (24 to 48) for devices to connect to.
• Routers provide connectivity between LANs and external networks, such as the Internet.
• A wireless router (Wi-Fi router/home router) is a multifunctional device that combines the roles of router, switch, wireless access point, and firewall into one.
• Firewalls secure the network by inspecting traffic that enters or exits the network, and allowing or denying it based on a set of configured rules.

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