Explain like I'm five · Security

What is a VLAN?

Virtual LANs, told as a story about a hallway split up with colored ribbons.

KitchenYardVaultStorageStudya guest knocks on the vault doorcooks, guests and clerks all share one hallway

One hallway, and everyone mixes.A guest laptop can knock on the vault door — exactly what the hallway watcher worries about.

three hallways?expensive and slowto build walls you'd have to build new hallways

Walls mean building whole new hallways.Three new hallways is expensive and slow.

KitchenYardVaultStorageStudyblue: cooksgreen: guestsred: clerks

A VLAN splits the hallway with colored ribbons.Ribbons instead of walls. Blue talks only to blue. One hallway, three neighborhoods.

The ribbonevery color has a number
Same color onlyshout, and only your color hears
Crossing colorsmeans passing a gatekeeper
Many colors, one passagebetween buildings they share the road
green→red× noto cross a color, you pass the gatekeeperone passage between buildingsall three ribbons travel togethera trunk

Crossing a color means passing the gatekeeper.A guest (green) heading for the vault (red) meets the gatekeeper and his list. Between buildings, one passage carries every color — a trunk.

KitchenYardVaultStorageStudyswapped the ribbonthe socket gatekeeper hands out ribbonsa ribbon is a promise, not a wall

A ribbon is a promise, not a wall.Swap the ribbon and you're across. So the socket gatekeeper hands out ribbons, and a real gatekeeper stands between colors.

In one breath

A VLAN = one hallway split into several with colored ribbons. Same color talks to same color; crossing colors means a gatekeeper.

Virtual LAN, IEEE 802.1Q. Ribbons are tags numbered 1 to 4094. Cut the ribbons finer and you get micro-segmentation — the hallway version of the castle that always asks.

When grown-ups say it

Tag · VLAN ID
The ribbon's color. Numbered 1 to 4094. The socket, not the person, hands out the ribbon.
Broadcast domain
How far a shout carries. Shout, and only your color hears.
Access port
A one-color socket. Plug in, get that color's ribbon. → the gatekeeper at every socket
Trunk
The passage every color shares. One passage between buildings, ribbons on, everyone together.
Inter-VLAN routing
The gatekeeper between colors. Green to red passes here. → the wall with many doors
VLAN hopping
Swapping ribbons. A thief's trick that exploits the ribbon being only a promise.
Native VLAN
How the ribbonless are treated. No ribbon? You count as this color. Thieves love it.
Micro-segmentation
Ribbons cut finer. Down to one room, one device. → the castle that always asks
Next story
The Fake Crowd at the Gate →
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