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.

#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.

#How to draw it in Capable

#A worked example

VLANs as labelled network bands:

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 ;
  }
}

#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.

#Related

Somebody will read this at 3am. Be kind.