An address plan that survives growth

Pick a private range with room

Every office network uses one of the private IPv4 ranges set aside for internal use: 10.0.0.0/8, 172.16.0.0/12 (172.16.0.0 to 172.31.255.255) and 192.168.0.0/16. Addresses in them are never routed on the internet, so you can use them freely inside the building.

Which one you choose matters more than people think. Almost every home router hands out 192.168.0.x or 192.168.1.x. If your office uses the same range, a member of staff connecting over VPN from home ends up with two networks that look identical, and traffic for the file server goes to their kitchen instead. That is why Kestrel & Vale moved from 192.168.1.0/24 to 172.16.40.0/22 when they added the VPN — a block of four /24 segments that no consumer router uses by default.

Choose an address range for the office you will have in five years, not the one you have today.

Size the segments

A /24 segment has 254 usable addresses, which is plenty for most small offices and easy to read: the first three numbers identify the segment, the last one identifies the device. Resist the temptation to use odd sizes like /26 to “save” addresses — private space is free, and uniform /24s make scanning, firewall rules and troubleshooting much simpler.

Two conventions make the plan predictable. The gateway is always .1. Fixed addresses live below the DHCP pool, so a glance at an address tells you whether something was assigned on purpose or picked up a lease.

Static, reserved or DHCP?

Each device gets its address one of three ways. Choosing deliberately is half the plan.

Reservations are usually the best option for anything people type the address of. The device keeps its address, and the DHCP server keeps a central record of who has what — which is exactly the record you want when a scan shows something unexpected. Kestrel keeps statics for just two devices: the router and KT-DC1, because DHCP cannot hand out an address to the DHCP server itself.

Names that tell you something

Your scans will show computer names next to addresses, so make the names useful. Kestrel uses a short prefix for the firm, then a type, then a number: KT-FS1, KT-PRN2, KT-PC17, KT-LT03. Anything that does not follow the pattern — a DESKTOP-4G7HQ2 or a LAPTOP-8F3KD — is either brand new or was never set up by IT, and it stands out immediately in a results list.

• Keep names to 15 characters or fewer; that is the NetBIOS limit, and Network Scanner can show NetBIOS names.
• Use letters, digits and hyphens only.
• Put the name in DNS for anything with a fixed address, so that scans can resolve it either way.

Check the plan against DHCP

A plan on paper is only useful if the network matches it. On a Windows DHCP server you can list the reservations and scopes with PowerShell from your own PC (this uses Windows’ DHCP Server module, part of the Remote Server Administration Tools — not Network Scanner).

Compare the output with your plan. Every fixed device in the plan should appear either here or as a static address you can confirm on the device. Anything in the plan that is missing is a job for today; anything here that is not in the plan is a question for lesson 7.

Turn the plan into scan targets

This is where the plan pays off. Network Scanner keeps its targets in a list on the Scan tab, and each entry can be a range, an expression or a list of names. Build them straight from the plan.

1. One range per segment you will scan often

   Add an IP range named “Staff” from 172.16.40.1 to 172.16.40.254. The Detect IP Range button fills in the range of the PC you are sitting at, which is a quick way to check you are where you think you are.

2. One expression for the fixed segments

   Add an expression named “Servers and cameras”: 172.16.42-43.1-254. Expressions use a hyphen for a range and a comma for a list in any octet, so 172.16.42.5,10,20,31-32 would cover exactly the five fixed server-segment devices.

3. Leave the guest segment out on purpose

   Do not add 172.16.41.0/24. It is out of scope and isolated anyway; a range that always comes back empty only teaches you to ignore empty results.

You will add the third kind of target — a list of names — in lesson 4, once the program is installed. If you have not installed it yet, the install guide walks through it.

Exercise: write your address plan

Create C:\LANScan365\notes\ip-plan.xlsx (or a Markdown table if you prefer) with one sheet per segment. Columns: address, name, device, method (static / reservation / DHCP pool), owner, notes. Then:

• Mark the gateway, the DHCP pool and the reserved block on each segment.
• Fill in every fixed device from your lesson 1 map.
• Compare with your DHCP server’s reservations and note any mismatch.
• At the bottom, write each in-scope segment as a range or an expression, ready for lesson 4.

Staff                172.16.40.1 - 172.16.40.254        (range)
Servers and cameras  172.16.42-43.1-254                  (expression)
Fixed devices        KT-DC1, KT-FS1, KT-NAS, KT-PRN1,
                     KT-PRN2, KT-NVR, KT-GW              (name list, lesson 4)
Out of scope         172.16.41.0/24 guest