Interactive lab · Networking
A working model of a small network. Send a packet from a PC to the Internet and watch it hop through switches, a firewall, and a router — then break things on purpose and learn to find the fault.
Simplified simulation. It teaches real concepts with simulated timings — it never measures or touches your actual connection.
The simulator
Pick a start and a destination, press Run test, and follow the packet hop by hop. Arm a fault first if you want to play network detective. Click any device or cable to inspect it.
Fault to inject
Inspector
Click any device or cable in the diagram to learn what it does.
Diagnostic log
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
Seven devices, four jobs. Everything on a home or small-office network is some version of these.
Connects devices on the same local network and forwards frames between them using MAC addresses — the hardware address burned into every network port. It learns which device lives on which port by watching traffic, so it can send each frame only where it needs to go. Two PCs on one switch can talk without anything else involved.
Connects different networks together using IP addresses. When a packet's destination is not on the local network, the router decides which path it should take next. Your home router is the border between your network and your internet provider's network.
Inspects packets against a rule list and decides what passes. Typical home rule: anything you start (like loading a page) may come back in; unsolicited traffic from outside is dropped. It does not speed anything up — it is a bouncer, not a highway.
Just a computer whose job is to answer requests — files, in this lab's case. When "the network is down," surprisingly often the network is fine and a server like this one is simply off or crashed.
Network-attached storage: a box of hard drives with a tiny computer attached, so every device on the network can reach the same files. It behaves like a small, single-purpose server.
Where packets are born. A PC needs two things to reach the Internet: its own address on the local network, and the address of its default gateway — the router it hands off anything non-local to. Get the gateway wrong and local traffic still works while the Internet mysteriously does not.
Follow one packet
This is the default test above. Run it and watch each step happen.
Your PC wraps the request — say, "fetch this page" — in layers: the web request inside a TCP segment inside an IP packet inside an Ethernet frame. The destination IP is somewhere on the Internet, which PC-1 knows is not local.
The local switch reads the destination MAC address. It is the router's, so the frame goes out the port the router lives on. The switch learned that mapping by watching earlier traffic — that learning is the whole trick of a switch.
The packet passes the firewall, which sees outbound traffic your PC started and allows it. The firewall works at the boundary, judging each packet against its list.
The router looks at the destination IP, confirms it is not local, and forwards the packet toward your internet provider — the next hop on the way across the Internet.
Across many more routers, the packet reaches its destination. None of that is simulated here; the cloud is where this lab's model ends and the real Internet begins.
The destination answers, and the reply travels the same path in reverse. When PC-1 gets it, the test passes. That round trip is what "ping" measures in the real world.
Fault injection
Each fault is a simplified version of something that genuinely happens. Arm one above, run the test, and read the diagnosis.
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.
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.
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.
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.
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."
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
Questions
Yes. Like everything in the PlainLogic lab, the Network Operations Lab is free to use as often as you like. No account, no sign-up, no paid tier.
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.
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.
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.
No. The whole lab runs in your browser tab, on desktop and mobile. Nothing is uploaded anywhere.
Keep exploring
Real networks carry real data. Watch live weather, alerts, earthquakes, and radar flow through an operations console.
Convert text and photos to PDF, pull text back out — entirely on your device.
Games, experiments, the Mini Lab block builder, and the blog — the full bench.