Switch
Connects devices on the same local network, forwarding frames by MAC address — the hardware address on every port. It learns which device lives on which port by watching traffic, so two PCs on one switch can talk with nothing else involved.
Interactive lab · Networking
Network Operations Lab
Send a packet from a PC to the Internet, watch it hop through switches and a router — then break things on purpose.
The simulator
Watch a packet find its way
Pick a start and a destination, press Run test, and follow the packet hop by hop. Arm a fault to play network detective — select any device or cable to inspect it.
Simplified simulation. It teaches real concepts with simulated timings — it never measures or touches your actual connection.
Fault to inject
Inspector
Nothing selected
Click any device or cable in the diagram to learn what it does.
Diagnostic log
Hop by hop
- readyChoose a route and press Run test. Timings shown are simulated, not measured.
One fault at a time, on purpose — real troubleshooting starts by isolating a single change. Arming a fault suggests the route that shows it off, but you can still pick any start and destination.
Plain-language networking
What does each box do?
Seven devices, four jobs. Everything on a home or small-office network is some version of these.
Router
Connects different networks using IP addresses. If a packet's destination isn't local, the router picks the next hop — your home router is the border between your network and your provider's.
Firewall
A bouncer for packets: it checks each one against a rule list. Anything you started may come back in; unsolicited traffic from outside is dropped. It doesn't speed anything up.
File server
Just a computer whose job is answering requests. When "the network is down," surprisingly often the network is fine and a server like this is simply off.
NAS
A box of hard drives with a tiny computer attached, so every device reaches the same files — a small, single-purpose server.
PC
Where packets are born. It needs its own local address plus a default gateway — the router it hands non-local traffic to. Get the gateway wrong and local traffic works while the Internet mysteriously doesn't.
Follow one packet
PC-1 → the Internet, hop by hop
Three packets, four numbered stops. Every packet carries a real label — a photo, a video call, a game move — so you can follow actual data, not dots.
Watch your photo travel to the internet.
Three packets are on their way — each one carries a real label.
- 1PC builds the packetYour photo is wrapped into a packet (a small chunk of data) and sent out its network port.
- 2Switch forwards itReads the destination address and sends the frame out the right port — local delivery, no router needed.
- 3Router picks the pathThe destination isn't on the local network, so the packet is forwarded toward your provider.
- 4The InternetYour photo arrives — at mom's phone, the game server, the video call. The reply travels the same path in reverse.
Fault injection
Six realistic ways to break it
Each fault is a simplified version of something that genuinely happens. Arm one above, run the test, and read the diagnosis.
- Unplugged cable
The most common "network problem" in any office. The switch sees the port go dark and simply has nowhere to send frames for that device. Fix: plug it back in. The lab's suggested route is PC-1 → PC-2.
- Shut switch uplink
A port can be administratively disabled — or fail. Everything below that switch is cut off at once, which is why one dead uplink can look like "the whole network is down" from the wrong side of it.
- Server powered off
The path is perfect and the packet arrives — but nobody answers. This is the fault behind half of all "is the internet down?" confusion: the network is fine, a computer is off.
- Wrong default gateway
PC-1 can still reach the file server and the other PC, but the Internet is unreachable — it has no correct route off the local network. Try both destinations to feel the difference.
- Slow link
Every packet arrives, just late. The test passes, slowly. Slow is not the same as broken — an important distinction when someone says "the wifi is down" and means "this page took four seconds."
- Lossy link
Some packets vanish mid-flight. The PC waits, retransmits, and gets through — exactly what TCP does on a flaky connection. Downloads crawl; video calls stutter.
Behind the build
What powers this experiment
- Networking concepts
- Frames vs. packets, MAC vs. IP addressing, switching, routing, firewall rules, and the default gateway — the working vocabulary of "why can't I reach that."
- Graph visualization
- The topology is a small graph: devices are nodes, cables are edges. Everything is drawn as resolution-independent SVG, so it stays sharp on any screen and scales from phones to desktops.
- State simulation
- Each device and link carries a state — up, down, degraded, off — and faults mutate that state. Routes are computed by searching the graph, the same idea real routing protocols use at a vastly larger scale.
- Fault diagnosis
- Running a test walks the computed path hop by hop, narrating what each device does with the packet. When a hop fails, the lab reports the cause in plain language instead of an error code.
- Interactive rendering
- Packets are animated along link geometry with requestAnimationFrame, with instant fallbacks when reduced motion is preferred. No game engine, no heavy dependencies — just the DOM and some math.
Questions
Fair questions
Is it free?
Yes. The Network Operations Lab is free to use as often as you like — no account, no sign-up. PlainLogic may introduce optional accounts or paid features in the future, but the core labs are free to use today.
Does it test my real network?
No. This is a simplified simulation with a made-up network. The packets, devices, and timings are all simulated in your browser so you can learn the concepts safely. It never measures or touches your actual connection.
What does a network switch actually do?
A switch connects devices on the same local network and forwards frames between them using MAC addresses. It learns which device is plugged into which port by watching traffic, then sends each frame only out the right port.
What is the difference between a switch and a router?
A switch moves traffic inside one local network using hardware (MAC) addresses. A router connects different networks together using IP addresses and chooses the path each packet takes next. In this lab, switches handle PC-to-PC traffic and the router handles anything headed to the Internet.
Do I need to install anything?
No. The whole lab runs in your browser tab, on desktop and mobile. Nothing is uploaded anywhere.
Keep exploring
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Convert text and photos to PDF, pull text back out — entirely on your device.
PlainLogic home
Games, experiments, the Mini Lab block builder, and the blog — the full bench.