Every network, from a home Wi-Fi setup to a data centre, is built from a handful of device types arranged in a particular layout. Understanding network devices and topologies helps you design networks, troubleshoot problems and talk confidently with engineers.
Common network devices
| Device | OSI layer | What it does |
|---|---|---|
| Modem / ONT | 1–2 | Connects your network to the ISP over DSL, cable or fibre |
| Network interface card (NIC) | 1–2 | Connects a device to the network; has a MAC address |
| Repeater | 1 | Regenerates a weak signal to extend distance |
| Hub | 1 | Repeats every signal to all ports (obsolete) |
| Switch | 2 (some 3) | Forwards frames to the right port using MAC addresses |
| Router | 3 | Connects networks and forwards packets by IP address |
| Wireless access point | 1–2 | Connects Wi-Fi devices to the wired network |
| Firewall | 3–7 | Filters traffic based on security rules |
| Gateway | Various | Translates between different networks or protocols |
Modem and ONT
A modem converts signals between your network and the ISP’s line. With fibre broadband, an ONT (optical network terminal) does this job.
Network interface card
Every connected device has a NIC, wired or wireless. Each NIC has a unique MAC address. Read what is a MAC address.
Hub vs switch
A hub sends every frame to every port, which wastes bandwidth and causes collisions. A switch learns where devices are and sends frames only to the right port. Switches replaced hubs years ago.
Router
A router connects different networks, such as your office LAN and the internet. It reads IP addresses and chooses the best path. Home routers usually combine a router, switch, Wi-Fi access point and firewall in one box.
Firewall
A firewall allows or blocks traffic based on rules. Next-generation firewalls also inspect applications, detect intrusions and filter websites.
Gateway
A gateway connects networks that use different protocols or formats. The term “default gateway” also describes the router that devices use to leave their local network.
Network topologies
A topology describes how devices are connected. The physical topology is the actual cabling, while the logical topology is how data flows.
| Topology | Description | Pros | Cons |
|---|---|---|---|
| Bus | All devices share one cable | Cheap, simple | One break stops everything; obsolete |
| Ring | Each device connects to two neighbours in a loop | Predictable performance | A single failure can break the ring unless it is dual |
| Star | All devices connect to a central switch | Easy to manage; one cable failure affects one device | The central switch is a single point of failure |
| Mesh | Devices have multiple connections to each other | Very resilient | Expensive and complex |
| Tree (hierarchical) | Stars connected in layers | Scalable, organised | Depends on upper-layer links |
| Hybrid | A mix of topologies | Flexible | More complex design |
Topologies in real networks
- Offices use a star or tree design: access switches connect to distribution and core switches.
- Data centres often use a leaf-spine design, a form of partial mesh, for predictable performance.
- Wireless mesh systems extend Wi-Fi coverage in homes and campuses.
- WAN backbones use partial mesh for redundancy between sites.
Choosing a design
For most organizations, a hierarchical star design with redundant core links works well. Add redundancy where an outage would hurt the business most, such as uplinks, core switches and internet connections.
Related guides
Sources
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