Target Audience

This article is intended for those looking for a primer on basic networking terms and concepts.


Switches, routers, and firewalls are electronic devices used to build data networks. They serve as essential components of the Internet, ferrying information rapidly from one computer to the next. In many commercial networks, a separate piece of hardware handles each of these functions. For small office/home office use, the switch, router, and firewall are typically combined into one convenient, low-cost unit.


A switch connects multiple computers and mobile devices together into a local network.

It serves as a central point through which computers on that local network communicate with each other. A switch can handle simultaneous connections between dozens of computers, with no connection interfering with any other. However, a switch cannot connect to other networks by itself–it requires a router to communicate with other networks.

A network is a group of computers that exchange data. Networks may be simple, such as a home office with PCs and mobile devices, or they may be large and complex, like the Internet.


A router connects separate networks, allowing information to route from one to the other. The networks may be physically separate, such as a home office network and the Internet, or logically separate, such as subnetworks that share cabling. In this sense, a router forwards data between networks in much the same way as a postal distribution center forwards mail between cities. Routers can also create logically separate networks from physically connected ones, preventing broadcast traffic on one subnetwork from interfering with another.

A broadcast sends data from a single device to all other devices on a network (one-to-all). Broadcasts are used to manage data communications between computers rather than data transfers. A common use of broadcasts is an ARP (Address Resolution Protocol) request, in which a computer broadcasts a request on its network to learn what device has a particular IP ad


A network firewall is a security device that puts up a barrier between a local network and the Internet. The firewall acts as a filter, allowing or restricting data traffic between the network it protects and other networks. Firewalls are flexible, allowing you to modify the blocking rules, such as by IP address, by protocol (TCP, UDP, ICMP), by port, or for software applications and services.

 An IP (Internet Protocol) address is a number that identifies a particular computer or networked device, much as a street address identifies an individual building. IP addresses come in two main types. The most common, IPv4, consists of four numbers, from 0 to 255, separated by periods–e.g., IPv6 is newer and allows a much greater number of unique addresses (IPv4 currently faces the problem of running out of unique addresses). An IPv6 address is made up of 8 hexadecimal numbers of four digits each, separated by colons, such as 2001:DB8:2AE1:1:3622:104:9050:1


A network protocol is a set of rules describing how networks handle the transfer of data. Common examples include Transfer Control Protocol (TCP), User Datagram Protocol (UDP), and Internet Message Control Protocol (IMCP).


A port is a number (between 0 and 65535) that identifies a logical “slot” or pigeonhole through which data passes on its way to or from an application or program. The IP address and port number often go together, making the port a “sub address” similar to an apartment number that distinguishes one unit in a building. Many ports have been traditionally designated for certain uses–for example, Web traffic most commonly uses ports 80 and 443.


Software Firewall

Microsoft Windows, Apple’s Mac OS X, and other modern computer operating systems come with a software firewall built in. A software firewall performs the same task as the hardware version, protecting the computer from intruders over the Internet. In many instances, the software is turned on by default, providing security for computer users who don’t have a hardware firewall. Software and hardware firewalls can coexist without any trouble on the same network, improving security through redundancy.

Combination Devices

Modern home network devices now provide the functionality of a firewall, router, and switch in a single unit. Combining these services has greatly lowered the cost of home networks as well as simplified setup and maintenance. The switch allows local devices to communicate with each other and share a common Internet service; the router sends data to the Internet from the home network; and the firewall keeps the local network safe.



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