2.3Network equipment (modem, switch, router, Wi-Fi)
The essentials in 30 seconds
- The modem terminates the ISP line; the router connects networks and acts as gateway, DHCP server and NAT.
- The switch connects machines inside the wired LAN; the access point adds Wi-Fi.
- A box often combines the four functions: the scope of the failure (one workstation, one segment, the whole site, Wi-Fi only) points to the right equipment.
Running mini-case — Sofiane maps the SME's network
Sofiane's distribution SME, in Algiers, is moving part of its workstations. One morning, only the sales reps' Wi-Fi devices go down, while the office's wired workstations keep working. Sofiane draws the chain: ISP line → modem (inside the box) → router (gateway 192.168.1.1, DHCP, NAT) → floor switch → wired workstations, plus an access point for Wi-Fi. Since the failure only affects wireless, he targets the access point: he restarts it and repositions its antenna, and coverage returns. He notes the rule: link the scope of the symptom to the corresponding equipment.
Standalone case for this section: it returns in the lesson, the diagram, the script and the 48h challenge of section 2.3.
1. The modem — the line's entry point
The modem terminates the access provider's line (ISP) and converts it into a usable network signal: it is the entry point of the connection. If it fails, nothing goes through any more, for anyone.
2. The router — connecting networks
The router connects different networks (the local network and the Internet) and routes traffic between them. It is the gateway; it hands out addresses (DHCP) and performs the NAT to the public address. When Sofiane looks for who is the “way out”, it is the router.
3. Switch, access point and all-in-one box
The switch connects machines inside the local network and sends each frame only to the relevant port: it extends the wired network. The access point adds wireless: it lets Wi-Fi devices join the wired network. In small installations, a single box combines modem + router + switch + access point. Understanding the roles separately remains useful: knowing which function fails indicates where to look.
🔎 Concrete example — 🔎 Concrete example — Locating a failure by the equipment
Three symptoms, three different leads:
Two PCs on the same switch cannot see each other -> switch / cable
The whole site loses Internet at once -> modem / ISP line
Only the Wi-Fi devices go down -> access point
Reading : each piece of equipment has a role
Diagnosis : link the scope of the problem to the equipmentReading: each piece of equipment has a role; the scope of the failure points to the right culprit.
Lesson: the scope (one workstation, one segment, the whole site, Wi-Fi only) designates the equipment to examine.
Section vocabulary
- Modem
- Terminates the ISP line and converts it into a usable network signal: the entry point of the connection.
Simple example: The whole site loses Internet: Sofiane looks at the modem and the ISP line.
What it is not: a switch that only connects the workstations of the LAN.
Reflex: line entry → modem.
- Router
- Connects networks (LAN/Internet), routes traffic; it is the gateway, hands out addresses (DHCP) and does the NAT.
Simple example: The SME's router carries the gateway 192.168.1.1.
What it is not: a simple wired splitter without routing.
Reflex: between networks + gateway → router.
- Switch
- Connects machines inside the local network (wired) and targets each port.
Simple example: Two PCs on the same switch no longer see each other: Sofiane checks this switch and the cables.
What it is not: the access point that adds Wi-Fi.
Reflex: inside the LAN → switch.
- Access point
- Adds Wi-Fi connectivity to the wired network.
Simple example: Only the Wi-Fi devices go down: Sofiane restarts the access point.
What it is not: a router that routes between networks.
Reflex: wireless → access point.
- Box (all-in-one)
- Combines modem, router, switch and access point in a single device.
Simple example: The SME's box groups the four functions.
What it is not: a device dedicated to a single function.
Reflex: four functions combined → box.
In practice — In practice — Mapping the network and locating a failure
- Draw the network: line → modem → router → switch → workstations, plus the access point, like Sofiane.
- Indicate who is the gateway and who hands out the addresses (DHCP).
- For each piece of equipment, note a symptom that would point to it.
- Identify which functions your installation's box corresponds to.
Step-by-step script — mapping and locating like Sofiane (4 min)
1) Trace the chain: ISP line → modem → router → switch → workstations, plus access point. 2) Annotate the router: gateway, DHCP, NAT. 3) For each element, write a typical symptom: a mute segment → switch/cable; the whole site cut off → modem/line; Wi-Fi alone down → access point. 4) Spot the functions combined in your box. 5) Keep this diagram: it serves as a map for the diagnostics of section 2.4.
Always link the scope of the problem to the equipment: it is the reflex that avoids restarting everything at random.
Copy-paste template — my equipment map
ISP line -> modem (converts the line)
-> router (gateway 192.168.1.1, DHCP, NAT)
-> switch (wired LAN)
-> access point (Wi-Fi)
Box = modem + router + switch + access point
Symptoms: segment -> switch | whole site -> modem/line | Wi-Fi -> access pointA mute wired segment
Two workstations on the same switch no longer communicate: Sofiane checks the switch and the cables.
The whole site cut off
No one has Internet at once: Sofiane looks at the modem and the ISP line.
Only Wi-Fi goes down
The wired workstations work, not the Wi-Fi: the lead is the access point.
Spotting the box
Sofiane identifies which functions (modem, router, switch, Wi-Fi) his box combines.
✓ Best practices
- Link the scope of the failure to the equipment.
- Place the access point centrally and high up.
- Give the network equipment a stable address.
✗ Common pitfalls
- Confusing switch (in the LAN) and router (between networks).
- Believing “weak Wi-Fi = slow Internet”.
- Plugging in two competing DHCP servers.
Key takeaways
- Modem = converts the line; router = connects networks (gateway/DHCP/NAT).
- Switch = the LAN's machines; access point = Wi-Fi.
- A box often combines the four functions.
- Symptom → equipment: cabling/switch, modem/line, or access point.
48h challenge — apply it tomorrow
Like Sofiane, draw the map of your network: line → modem → router → switch → workstations, plus the access point. Annotate the router (gateway, DHCP, NAT) and write, for each piece of equipment, a symptom that would point to it. Specify in one sentence which functions of your box are combined.
- I distinguish modem, router, switch and access point.
- I can draw a simple network and place the gateway in it.
- I link the scope of a failure to the equipment concerned.
Frequently asked questions
What is the difference between a switch and a router?
The switch connects machines WITHIN a network; the router connects DIFFERENT networks (and goes out to the Internet). A box often combines both.
My Wi-Fi is weak in some rooms although the fibre is fast?
Access throughput ≠ Wi-Fi coverage. Reposition the access point, reduce obstacles, or add an access point — the router and the line are not at fault.
Which piece of equipment connects networks to one another and acts as gateway?