Subnet Divider (FLSM)
Enter a base network and split it into equal-size subnets: by subnet count, by new prefix or by hosts per subnet. I list them all with mask, range, broadcast and hosts. All in your browser.
Generated subnets
| # | Network / CIDR | Mask | 1st host | Last host | Broadcast | Usable |
|---|
FLSM splits the base network into equal-size subnets: they
all share the same prefix and the same step. When you fix by subnet count I
borrow bits up to the nearest power of 2, so the real count
may be larger than requested. With hosts per subnet I always reserve
network and broadcast.
Runs locally in your browser · no sign-up · nothing leaves your browser
How it works
The divider takes a base network in CIDR format (for example 192.168.1.0/24) and splits it into equal-size subnets (FLSM, Fixed Length Subnet Mask) according to the criterion you choose: number of subnets, new prefix, or hosts per subnet. For every subnet it lists the network with its CIDR, the mask, the first and last host, the broadcast and the usable hosts.
The math is the classic bit borrowing: if you ask for N subnets it borrows ceil(log2(N)) host bits and the new prefix is the sum (the actual count is rounded up to the next power of 2); if you ask for H hosts per subnet it uses H + 2 addresses (reserving network and broadcast) to pick the tightest prefix. Every block stays aligned and the step between subnets is 2^(32−prefix), with the /31 (RFC 3021) and /32 exceptions that skip the subtraction.
Example: splitting 192.168.1.0/24 into 4 equal subnets
- 4 subnets require 2 borrowed bits (
2^2 = 4): the prefix goes from /24 to /26, mask255.255.255.192. - Each subnet holds
2^(32−26) = 64addresses; the step between subnets is 64. - Result:
192.168.1.0/26,.64/26,.128/26and.192/26, each with 62 usable hosts.