Subnetting for installers who need answers fast on site

The first question is always host count

Before choosing a subnet, count what will live on it. Do not count only the current devices. Include NVRs, switches with management IPs, access points, future cameras, printers, access-control devices, and spare room for growth.

Simple working rule

• Small isolated camera job: a /24 is usually comfortable.
• Tiny segments with very few devices: /27 or /28 can work if the layout is clear.
• Mixed office and CCTV on one flat network: avoid this if you can.

Why installers should care about segmentation

Even modest sites benefit when CCTV, staff devices, guest Wi-Fi, and server equipment are separated logically. This makes troubleshooting easier, reduces broadcast noise, and gives you cleaner options when remote access or firewall rules are needed later.

Gateway, DHCP, and static addressing

Installers often mix static and DHCP without a reservation strategy. That creates confusion fast. Use a clean rule for each site.

Practical default

• Infrastructure devices: static IP or DHCP reservation.
• User devices: DHCP pool.
• Document the gateway, subnet mask, DNS, and reservation range before handover.

When to separate CCTV from the office network

• When camera count is high
• When remote viewing is required
• When there are bandwidth complaints on the office side
• When the client expects cleaner security boundaries
• When the recorder and cameras should stay stable even if office devices churn

Field checklist before leaving site

1. Ping the gateway from a sample device on each segment.
2. Confirm the recorder, cameras, and switches use the intended range.
3. Check for duplicate static IPs.
4. Record final addressing in the handover document.
5. Store the addressing plan where the next technician can actually find it.

Take this with you on the next job

None of this needs to be memorized. Count devices first, pick a subnet size that leaves room to grow, decide the DHCP/static split before you touch a keyboard, and write the final addressing down where the next technician can actually find it. Those four habits solve most of the network problems that come from rushed installs.