Networking Hardware lessons
What is a network?
Opener: four computers on a switch. The MAC address table fills from each frame, flooding stops once it is full, and a hub mode floods everything.
A network is two or more devices linked so they can share data. Networking hardware is the cards, boxes and cables that carry that data.
Above, four computers share a switch. Each message they send is a frame, and the switch learns where each computer is from the frames it sees.
This course covers the devices in a typical home or office network. You will see what each one does and how they work together.
The devices in a home network
A typical home network has phones, laptops, a TV and maybe a desktop computer. They all connect to one box, usually called the router.
Example: a home network diagram that tours each device and its link to the router box.
Devices that plug in with a cable have a wired connection. Devices that connect by radio over Wi-Fi are wireless.
The router box links your home to your internet service provider (ISP). The ISP connects you to the rest of the internet.
Network cards and MAC addresses
Every device on a network has a network interface card (NIC). It may be a chip on the main board or a separate card, with a socket for a cable or an antenna for Wi-Fi.
Each NIC has a MAC address: a 48 bit number written as 12 hexadecimal digits. Colons split the digits into pairs, like 02:1C:7A:3E:91:0A.
Example: a MAC address split into its six bytes, each turned into 8 bits, adding up to 48.
A factory address starts with a code for its maker. Phones and laptops now often make up a random private address for each Wi-Fi network, so they are harder to track.
Practice: Spot a real MAC address
Practice: tap the pair that breaks a MAC address, or say it is valid.
Hubs and collisions
A hub is the simplest way to join computers by cable. Every frame that comes into one port is copied out of every other port.
Only one computer can send through a hub at a time. If two send at once, their signals clash in a collision and both must try again.
Example: two computers send at the same moment through a hub, then through a switch.
A repeater simply boosts a weak signal so it can travel further. Wired hubs and repeaters have been replaced by switches, though Wi-Fi extenders still repeat signals today.
Inside a switch
Here is a small 8 port switch with part of its lid cut away. Tour its ports, its lights and the chip that does the switching.
Example: a 3D tour of a small 8 port switch with its lid partly cut away.
How a switch learns
Every frame carries two MAC addresses: the receiver's and the sender's. A switch reads both.
First it notes the sender's address and port in its MAC address table. Then it looks up the receiver: a known address goes out of one port, and an unknown one is flooded out of every other port.
Example: a log of five frames through a switch, built from the simulation, with the table after each.
A frame sent to FF:FF:FF:FF:FF:FF is a broadcast, meant for every device. A switch always sends a broadcast out of every other port.
Practice: Where does the frame go?
Practice: given a MAC address table and a frame, pick the ports it goes out of.
Practice: Hub or switch?
Practice: sort statements into hub, switch or both.
Routers join networks
A switch joins devices into one local network. A router joins different networks together, such as your home and the internet.
Routers use IP addresses, which say which network a device is on. Data travelling between networks is called a packet.
Example: a router between two home networks and the internet, matching each packet to a row of its routing table.
The router's routing table lists each network and where to send its packets. Here /24 means the first three numbers must match, and 0.0.0.0/0 matches anything else.
The default gateway and the best path
A computer sends anything meant for another network to its default gateway. At home, that is the router box, often at 192.168.1.1.
Across the internet there are many routes between two places. Routers add up a cost for each route and pick the lowest, and they switch routes when a link fails.
Example: four routers with link costs. The packet takes the cheapest route, then reroutes when a link breaks.
Practice: Route the packet
Practice: tap the routing table row a router uses for a packet.
NAT: one address for the whole home
Addresses starting 192.168 are private: they only work inside a home or office. Your router has one public address that the internet can reach.
Network address translation (NAT) lets every device share that public address. The router swaps the private address for its public one on the way out, and swaps it back for the reply.
Example: three devices reach a website through one public address while the NAT table fills.
The router remembers each swap in a NAT table. A port number on each row tells the replies apart.
Wireless access points
A wireless access point (AP) links Wi-Fi devices to a wired network. It sends and receives frames by radio.
Wi-Fi uses three radio bands: 2.4 GHz, 5 GHz and 6 GHz. Lower bands reach further through walls, and higher bands carry more data but fade sooner.
Example: a phone moves away from an access point and the signal on each band is worked out from distance and walls.
Bigger homes often use mesh Wi-Fi: several access points that act as one network. Your device moves to the strongest one as you walk around.
Wi-Fi standards
Each generation of Wi-Fi has a simple name and an official IEEE name. Wi-Fi 6 is 802.11ax and Wi-Fi 7 is 802.11be.
The headline speed is a lab maximum, shared by every device on the access point. One phone in a real home gets a small part of it.
Example: Wi-Fi 4 to Wi-Fi 7 with their IEEE names, bands, headline speeds and realistic speeds.
Wi-Fi 7 routers and phones are now common, and its standard was published in 2025. Wi-Fi 8 is still being written, with the final version expected around 2028.
Practice: Match the Wi-Fi standard
Practice: match each Wi-Fi generation to its IEEE name or its key fact.
Modems and the home router box
A modem turns data into signals for the line into your home, whether a phone line, a TV cable or fibre. Its name comes from modulator and demodulator.
The box most people call a router holds several devices in one case. With full fibre, the modem part is often a separate small box called an ONT (optical network terminal).
Example: the home router box opened up, showing the modem, router, switch, access point, firewall and DHCP server inside.
Practice: Follow the path
Practice: order the hardware a request passes through on its way to the internet.
Firewalls
A firewall checks each packet and decides whether to let it through. It can be a separate device or software inside a router or computer.
Rules often name a port: a number that says which service a packet is for. For example, 443 is for secure websites and 22 is for remote login.
Example: packets checked against a firewall rule list from the top, where the first matching rule decides.
The firewall reads its rules from the top, and the first rule that matches decides. A last rule usually blocks anything the others did not match.
Practice: Which rule decides?
Practice: tap the firewall rule that decides a random packet.
Network topologies
A topology is the shape of a network: how its devices are linked. The four classic shapes are star, bus, ring and mesh.
Homes and offices use a star, with every device cabled to a switch. A mesh has many links, so data can go around a broken one.
Example: star, bus, ring and mesh networks with a cable to cut, showing who goes offline.
Bus and ring networks were common in the 1980s and 1990s. One broken cable could stop the whole network.
Practice: Name the topology
Practice: match descriptions and pictures to star, bus, ring or mesh.
The OSI model
The OSI model splits networking into seven layers, from the cable at layer 1 to the app at layer 7. Each layer does one job and relies on the layer below.
Going down the layers, each one wraps the data with its own information. A switch reads up to layer 2 (MAC addresses), and a router reads up to layer 3 (IP addresses).
Example: data travels down the seven layers, gaining a header at each, with the hardware that works at each layer.
To remember the layers from 1 to 7, try: Please Do Not Throw Sausage Pizza Away. That stands for Physical, Data link, Network, Transport, Session, Presentation and Application.
Practice: Which layer?
Practice: sort hardware and terms into OSI layers 1, 2 and 3.
Cables and connectors
Most wired networks use twisted pair copper cable with an RJ45 plug. Its category, such as Cat5e, Cat6 or Cat6a, sets how fast it can go.
A copper run can be at most 100 metres long. Fibre cable carries light instead, so it reaches much further and ignores electrical interference.
Example: the top speed of each cable type as the run gets longer.
Practice: Pick the right cable
Practice: pick the cheapest cable that meets a random distance and speed.