How do I subnet a home or small office network?
Updated 2026-10-22T00:00:00.000Z. Built with AI assistance and checked with automated tests.
Subnetting means cutting one block of IP addresses into smaller blocks, each one a separate network. To do it, pick a private range (for most homes and small offices, 192.168.0.0/24 is plenty), decide how many separate groups of devices you need, and give each group a CIDR prefix, such as /26 or /28, that holds its devices with room to spare. Each step is explained below, with a worked example at the end.
Start with the private ranges
Three address ranges are reserved for private networks (RFC 1918) and are not routed on the public internet:
- 10.0.0.0/8
- 172.16.0.0/12
- 192.168.0.0/16
Home routers often default to something in 192.168.x.x. That is fine for a small office too. The 10.0.0.0/8 range is huge, so it suits you if you expect many networks. Whichever you choose, avoid overlapping with the network at a remote site or a VPN you connect to, since overlapping ranges cause routing problems.
Understand CIDR and masks
CIDR writes a network as an address plus a prefix length, such as 192.168.0.0/24. The number after the slash is how many bits, counting from the left, belong to the network. The remaining bits identify devices on that network.
An IPv4 address has 32 bits, so the host portion is 32 minus the prefix. The number of addresses in a block is 2 to the power of the host bits. A /24 has 8 host bits, so 256 addresses. A /26 has 6 host bits, so 64.
The same information can be written as a subnet mask. A /24 is 255.255.255.0, and a /26 is 255.255.255.192.
Usable hosts. In ordinary IPv4 subnets, the first address is the network address and the last is the broadcast address. Neither can be given to a device. So usable hosts equal addresses minus 2. A /26 gives 62 usable hosts, a /28 gives 14, and a /30 gives 2. (Very small /31 and /32 blocks are special cases, used for point-to-point links and single hosts.) Your router’s address on that subnet also takes one of the usable addresses.
Plan by need, then size each subnet (VLSM)
Variable Length Subnet Masking (VLSM) simply means subnets do not have to be the same size. Plan like this:
- List your groups of devices, such as staff computers, phones and tablets, cameras, guests, and servers or printers.
- Count the devices in each group, including the router address.
- Add room to grow. Doubling the current count is a common rule of thumb, not a requirement.
- Pick the smallest block whose usable addresses cover that number. Block sizes are powers of two: 16, 32, 64, 128, and so on.
- Place the largest blocks first, so each block starts on a boundary that matches its size.
Separate subnets only isolate traffic if your equipment is set up for it. That generally means VLANs on a managed switch, with the router or firewall controlling what may pass between them. Devices on different subnets cannot talk to each other without a router. Check your equipment’s documentation for how to configure this.
Worked example: splitting 192.168.0.0/24
These device counts are sample numbers only. Suppose an office needs:
| Group | Devices now | Planned (about double) | Block chosen |
|---|---|---|---|
| Staff | 20 | 40 | /26 (62 usable) |
| Guests | 10 | 20 | /27 (30 usable) |
| Cameras | 8 | 16 | /27 (30 usable) |
| Printers and servers | 5 | 10 | /28 (14 usable) |
Place the largest first:
- Staff: 192.168.0.0/26, covering 192.168.0.0 to 192.168.0.63. Usable: .1 to .62.
- Guests: 192.168.0.64/27, covering .64 to .95. Usable: .65 to .94.
- Cameras: 192.168.0.96/27, covering .96 to .127. Usable: .97 to .126.
- Printers and servers: 192.168.0.128/28, covering .128 to .143. Usable: .129 to .142.
That uses addresses up to .143. The range from 192.168.0.144 through 192.168.0.255 is unallocated, which is a deliberate reserve for future subnets. A common convention is to give the router the first usable address in each subnet, such as 192.168.0.1 for staff. Each planned count above leaves room for the router address.
Common mistakes
- Forgetting the two unusable addresses (network and broadcast) in each subnet.
- Sizing for today’s device count with no growth room, which forces a renumbering later.
- Overlapping subnets, such as placing a /27 inside a block already given to another subnet.
- Starting a block on an address that is not a multiple of its size. Within a 192.168.0.0/24, a /26 must start at .0, .64, .128, or .192.
- Choosing a range that clashes with a VPN or another site.
- Assuming separate subnets are automatically secure. Without VLANs and firewall rules, they may not isolate anything.
- Not writing the plan down. Keep a simple table of subnets, ranges, and purposes.
This guide is general educational information. If your network carries sensitive data or has compliance requirements, confirm the design with a qualified network professional.