IP conflicts are almost always an administrative failure rather than a technical one: two people assigned the same address because neither had a single place to look. This sheet is that place.
Carve the space before you need it. Allocate subnets by purpose with room to grow, and leave deliberate gaps. Re-addressing a production network because a /24 filled up is a weekend nobody wants.
Record every static assignment centrally. Statics are invisible to DHCP, which means conflicts are discovered by an outage. Every static must be recorded here with an owner and a purpose, or it does not exist as far as the team is concerned.
Reclaim addresses when systems are decommissioned. Add the IP reclaim step to your decommission checklist. Unreclaimed addresses are why subnets appear full while half the space is unused.
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Keep utilisation current. Anything over 80% needs a plan before it becomes urgent.
| Subnet | VLAN | Purpose | Gateway | Usable addresses | In use | Utilisation | Site | Owner |
|---|---|---|---|---|---|---|---|---|
| 10.10.0.0/24 | 10 | Core infrastructure | 10.10.0.1 | 253 | 41 | 16% | LON | Infrastructure |
| 10.10.20.0/22 | 20 | Corporate clients | 10.10.20.1 | 1021 | 812 | 80% | LON | Infrastructure |
More free templates IT teams use alongside this one.
Network documentation fails because it is written once, as a project deliverable, and then diverges from reality within a quarter. This template is scoped to the things that change slowly and are expensive to rediscover at 02:00.
Network hardware fails quietly into unsupportability: firmware stops receiving security updates, support contracts lapse, and the vendor announced end-of-life two years ago. This inventory surfaces those dates before they become an incident.
The risk in decommissioning is rarely the shutdown; it is the dependency nobody knew about and the data nobody checked for. This checklist front-loads both, and ends with the licence and backup cleanup that pays for the exercise.
IP address management: the practice of planning and tracking how address space is allocated and used. At small scale a maintained sheet is sufficient; the point is having one authoritative place, not the tooling.
Record every static assignment in one place, keep static ranges strictly outside DHCP scopes, and reclaim addresses as part of decommissioning. Conflicts are nearly always two people assigning the same address without a shared record.
When reconciliation stops happening, typically past a few hundred static assignments or multiple sites. The signal is staleness rather than row count: once nobody trusts the sheet, people stop updating it and it degrades quickly.
