# Subnet and VLAN diagram

Subnet documentation usually starts as a diagram and ends as a spreadsheet, because diagrams get unreadable at about the twentieth subnet. Text-generated diagrams push that limit a long way out.

Keep the allocation table and the diagram on the same page, and let each do what it is good at.

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## When to reach for one

* Documenting IP allocation so two teams do not claim the same range.
* Planning a VLAN change with the current state visible.
* Troubleshooting, where the question is which VLAN something is on.

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## How to draw it in Capable

| **Route** | **Use when**                                                   |
| --------- | -------------------------------------------------------------- |
| nwdiag    | Networks as bands with addresses; generated, so it stays tidy. |
| draw.io   | Diagrams with firewall and routing detail alongside.           |

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## A worked example

VLANs as labelled network bands:

![Subnet and VLAN diagram](https://help.gocapable.com/images/att1431601157.svg)

The source, which you can paste into a new diagram and edit:

```
nwdiag {
  group {
    color = "#FFaaaa";
    web01;
    db01;
  }
  group {
    color = "#aaaaFF";
    web02;
    db02;
  }
  network dmz {
      address = "210.x.x.x/24"

      web01 [address = "210.x.x.1"];
      web02 [address = "210.x.x.2"];
  }
  network internal {
      address = "172.x.x.x/24";

      web01 [address = "172.x.x.1"];
      web02 [address = "172.x.x.2"];
      db01 ;
      db02 ;
  }
}
```

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## A few things that catch people out

* Record the ranges you have reserved but not used. That is where collisions come from.
* One diagram per site. A multi-site subnet diagram becomes a wall of numbers.
* Keep the diagram beside the change process, so it is updated when the change is made.

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## Related

[Rack diagramElevations that match what is in the room.](https://help.gocapable.com/diagrams/rack-diagram.html)

[Data center diagramFloor, rows, racks, and power.](https://help.gocapable.com/diagrams/data-center-diagram.html)

[ExamplesWorking diagrams you can copy.](https://help.gocapable.com/diagrams/examples.html)

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_Somebody will read this at 3am. Be kind._