How to keep an address plan that stays accurate

Every network has an address plan. Most of them are a spreadsheet that stopped being true some time ago.

IP address management is the unglamorous discipline of knowing what is where. It matters at exactly the moment it is missing: during an outage, when adding a site, or when the person who knew has left.

What belongs in it

• Every subnet, with its purpose and its VLAN.
• The gateway for each.
• The DHCP range, so you know which addresses are handed out automatically.
• Every static assignment — printers, cameras, servers, controllers, the switch management addresses.
• The VRF, if you use them, since addressing means nothing without it.

The static assignments are the part that matters most and gets recorded least. A DHCP server can tell you its own leases; nothing can tell you why 10.0.50.14 is a door controller.

Why spreadsheets drift

Not because spreadsheets are bad, but because nothing checks them. A row saying a gateway is 10.0.20.1 inside 10.0.30.0/24 sits there for years, because a spreadsheet has no opinion. By the time the error matters it has been copied into three other documents.

The value of a validated plan is that a mistake surfaces when it is typed, when it costs nothing, rather than during a change window.

Conventions worth adopting

Reserve a block for statics at the bottom of each subnet, below the DHCP pool. Everyone then knows where to look, and the DHCP server never fights with a fixed address.

Keep the DHCP pool in the same relative place in every subnet — the upper half is common — so a glance tells you whether an address is dynamic.

Write down why, not just what. "10.0.50.14 — camera" is useful. "10.0.50.14 — loading bay camera, replaced Mar 2025, PoE port gi1/0/14" is what somebody actually needs.

What to check periodically

Whether subnets are filling up. Whether static assignments have crept into DHCP ranges. Whether anything overlaps. Whether the plan still matches the running configuration — where it does not, one of the two is wrong and it is worth knowing which.

Frequently asked questions

What is the difference between IPAM and a DHCP server?

A DHCP server knows what it has leased right now. An address plan records what you intend, including everything statically assigned that DHCP never sees. They answer different questions and you need both.

Should I record every device?

Every static assignment, yes. Devices taking a DHCP lease do not need individual records — the pool is the record. It is the fixed addresses that become mysteries.

How do I stop the plan drifting from reality?

Validate it, update it as part of making a change rather than afterwards, and keep it where the next person will look. A plan nobody can find gets replaced by a new spreadsheet.

Is my plan stored on a server?

Not with this tool. Browser storage is off unless you turn it on, and the export is a file you keep. Nothing is uploaded at any point.