Network hardware

Network hardware is the collection of physical devices that allow computers and other electronic devices to communicate with one another by exchanging data within a network. 
It is the “tangible” part of a network: the part that helps manage the flow of information and enables data to reach the correct destination (Kurose & Ross, 2026; Tanenbaum et al., 2021)..

A network interface card (also called a network interface controller, NIC, network adapter, or physical network interface) is a digital interface implemented as an electronic circuit board. It performs the logical processing functions required to connect a device to a computer network and to transmit and receive data (Tanenbaum et al., 2021).

A network interface is the logical or physical connection point between a device, such as a computer, server, or smartphone, and a specific computer network. 
It converts data into signals that can be transmitted and has identifiers used for communication.

In everyday language, the terms network interface card and network interface are often used as synonyms, but it is technically useful to distinguish between them.

In a simple case, the relationship may be:
1 physical network card → 1 network interface

In this case, the situation is fairly intuitive: one physical card corresponds to one network interface.

However, in modern networks, the situation can be more complex.
A single physical network card can support or expose multiple network interfaces in order to communicate with several different networks.

For example, the device that connects a home network to the Internet must communicate with two different networks:

For this reason, it has multiple network interfaces, each dedicated to a different type of communication.

Each network interface has a unique identifier called a MAC (Media Access Control) address. 
A MAC address is a 48-bit identifier, expressed in hexadecimal format, assigned by the manufacturer to the network card during production (IEEE Standards Association, 2022).


A MAC address is used to identify a network interface within a local network. When a device sends data across the same local network, it places the recipient’s MAC address in the packet header so that the message can be delivered to the correct interface (IEEE Standards Association, 2022).

A switch acts like a “multi-socket power strip” and allows multiple devices to be connected to one another within a local network.
A switch learns which devices can be reached through its ports. When it knows which port is associated with the destination MAC address, it forwards the data only to that port (IEEE Standards Association, 2022; Kurose & Ross, 2026)..
For example, if a packet arrives on port 1 and is addressed to a device connected to port 3, the packet is forwarded only through port 3 rather than through all the other ports.
This is because, when a packet is received, the switch checks the destination MAC address in the packet header and uses it to determine which network interface should receive the packet.

Switches are commonly used in business networks, home networks, and many other situations where network traffic between connected devices must be managed and directed.

Switches are mainly used in LANs, or local area networks, where they connect nearby devices, for example within a home, school, or office.

A router is a device that connects different networks and forwards packets toward their destination network (Baker, 1995).
The term router comes from the English word “route”, meaning a path or course, because a router directs packets toward different devices.

From a logical point of view, a router is not very different from a switch.
It also connects different network devices, but with one important difference: a router can route packets between different networks.
Routers have multiple network interfaces, one for each network they must connect (Baker, 1995).
For example, a router connecting three different networks must have at least three network interfaces, one for each network.

A gateway is a particular type of router.
A gateway acts as an access point between a local network and an external network. An external network is a network that connects several local networks (Baker, 1995).
When a device on the local network wants to communicate with a device on the external network, several steps take place:

When the external network is the Internet, the gateway is often called the “default gateway”. Home routers act as default gateways.

Note: not all routers are gateways.

An ADSL or fiber modem is an electronic device that connects a computer to the Internet through a twisted-pair telephone line for ADSL or through optical fiber.
The modem is usually connected to the gateway, and its task is to convert digital data into a format suitable for the network.

The term modem comes from “MOdulator-DEModulator” because, in ADSL systems, it converts a computer’s digital signals into analog signals that can travel over telephone lines, and vice versa (Tanenbaum et al., 2021).

In a fiber-optic connection, which uses light to transmit packets across the network, the device used is technically an ONT (Optical Network Terminal).
The ONT converts electrical signals from the local network into optical signals for the fiber and, in the opposite direction, converts optical signals from the fiber into electrical signals that network devices can use (International Telecommunication Union, 2019).

An access point, also abbreviated as AP, is a network device that provides local wireless access to an electronic communication network (IEEE Standards Association, 2025).
The access point is connected to a switch and allows users to access the Internet without a wired connection.
This means that whenever we access the Internet wirelessly, our data is sent to or received from the access point. The access point forwards it to the switch, which sends it to the router; the router can then communicate with the Internet through the modem.

A hotspot is a location where an access point is available for Internet access. 
A hotspot is represented by the symbol shown below:

The term hotspot also refers to a function of a device, such as a smartphone, that shares its Internet connection.

An access point is most commonly associated with Wi-Fi, a wireless connection technology that uses radio waves (IEEE Standards Association, 2025).
A hotspot can be:

A firewall is a hardware or software network-security component that monitors incoming and outgoing traffic and applies security rules to allow or block specific communications (Scarfone & Hoffman, 2009).

In practical terms, a firewall acts as a filter that inspects data traffic and blocks dangerous or unwanted transmissions according to specific rules called ACLs (Access Control Lists).
Most firewalls include standard rules to which the end user can add customized rules according to their needs.

The firewall is positioned between the external network, including the Internet, and the internal network of a company or home, or even an individual user’s computer. 
A firewall works this way because, in simplified terms, the internal network is considered better known and more controllable, whereas an external network such as the Internet is treated as less trustworthy and potentially dangerous.

Most firewalls use one of two general rule-application policies (Scarfone & Hoffman, 2009):

A modem router is a device that performs the functions of both a modem and a router (Kurose & Ross, 2026). 
In practice, as well as serving as an Internet gateway, it allows all the devices in a home to communicate with one another.

For many years, people have incorrectly called the device used to connect to the Internet a “modem”, as in the case of devices such as the TIM HUB or Fast Gate.
In reality, these units combine several devices in a single box: