LAN, WAN & Reading a Network Diagram
What is it?
A LAN (Local Area Network) is a network in one place — an office, a home, a floor — where devices reach each other directly. A WAN (Wide Area Network) connects LANs across distance; the internet is the biggest WAN. A network diagram is the map: boxes are nodes, lines are links, and a special device (the router/gateway) is where a LAN meets the wider world.
Why it matters
Whether two machines are on the same LAN decides whether their traffic stays local or has to cross a router to reach the wider network. Reading a diagram is how you answer that at a glance, before touching any tool.
Where you see it
Every architecture diagram, office IT plan and cloud network drawing: a LAN of devices behind a router, connected through the internet (WAN) to other sites and services.
What normal looks like
Local devices grouped behind one router; traffic between them stays on the LAN; traffic to the outside goes through the router to the WAN. The diagram matches the physical wiring and the logical grouping agrees with it.
What suspicious looks like
A mismatch between physical and logical: two devices plugged into the same switch but placed in groups that are not allowed to talk, or a device that is physically local but logically has to cross a router to reach its neighbour. These mismatches are the root of a large share of 'it should work but doesn't' problems.
How analysts investigate
By locating both nodes on the diagram and asking: are they in the same LAN group? If yes, the traffic is local (no router involved). If no, trace the path through the router(s) to the destination and check each hop.
Common beginner mistakes
- Assuming that because two devices are plugged into the same box, they can automatically talk. Physical connection is necessary but not sufficient — logical grouping (which you will meet as subnets and segments) can still keep them apart.
- Reading a diagram as decoration instead of a map. Every line means 'these can reach each other', and every router symbol means 'a boundary the traffic must cross'.
Meridian's main office is one LAN: laptops, desktops, printers and a few local servers, all able to reach each other directly. But the payroll system runs in a cloud data center on the other side of the country. When an accountant opens payroll, their traffic cannot stay local — it has to leave the office LAN, cross the internet (a WAN), and arrive at a completely different LAN in the cloud.
There are two ways to look at the same network, and confusing them causes endless trouble. The physical view is the wiring: what is plugged into what. The logical view is reachability: who is actually allowed to talk to whom. They usually agree, but not always — two devices can share a cable and still be kept in separate logical groups that cannot reach each other. When you read a diagram, you are reading the logical view: lines mean 'can reach', and the router symbol marks a boundary.
Reading Meridian's diagram to answer one question
Two questions land on your desk: (1) can the accountant's desktop print to the office printer, and (2) can it reach the cloud payroll server? Answer both from the diagram alone.
Locate both endpoints of question 1 and check their LAN.
The desktop and the printer are both drawn inside the same office LAN, behind the same router. Same LAN means local delivery — no router needed, no WAN involved. Answer to (1): yes, and the traffic never leaves the office. A beginner might over-think this; the diagram answers it immediately.
Locate the endpoints of question 2 and trace across the boundary.
The desktop is in the office LAN; the payroll server is in a different LAN in the cloud. Different networks, so the path must cross the office router, out over the internet (WAN), to the cloud router, and finally to the server. Answer to (2): yes, but only if every hop on that path works — and there are now several.
Turn the two answers into a troubleshooting instinct.
The difference matters the moment something breaks. If printing fails, the problem is inside the office LAN — a short list. If payroll fails, the fault could be the office router, the internet path, the cloud router, or the server — a longer chain to check in order. Reading the diagram told you the length of the path, and therefore where to start looking, before you ran a single command.
Quick check
Two desktops are drawn inside the same office LAN, behind the same router. When they exchange a file, does the traffic cross the router?
A quick self-check — it doesn't affect your XP or progress.
Quick check
Two devices are plugged into the same physical switch, but a diagram shows them in separate logical groups that are not permitted to communicate. Can they talk?
A quick self-check — it doesn't affect your XP or progress.
Sign in to save your progress on the server.