Developer tools
VLSM subnet planner
Split one network into right-sized subnets for departments, links and VLANs.
A clear answer. Here’s how.
Each request needs hosts + 2 addresses (network and broadcast), rounded up to the next power of two. Blocks are placed largest first from the start of the parent network, which keeps every block aligned to its own size. A request for two hosts becomes a /30, or a /31 if you choose RFC 3021 links. The plan reports the addresses left over and fails if the parent is too small. It does not add growth headroom, so size requests with spare capacity.
See a worked example
Worked example
A fixed demonstration, separate from the values you enter above.
- Parent network
- 192.168.10.0/24
- Two-host links
- Use /30 (two usable hosts, classic)
- Subnet requests (CSV)
Name,Hosts Sales,50 Engineering,25 Guests,10 WAN link,2
Example result
| Subnet | Hosts needed | Prefix | Network | First usable | Last usable | Broadcast | Mask | Usable hosts |
|---|---|---|---|---|---|---|---|---|
| Sales | 50 | /26 | 192.168.10.0 | 192.168.10.1 | 192.168.10.62 | 192.168.10.63 | 255.255.255.192 | 62 |
| Engineering | 25 | /27 | 192.168.10.64 | 192.168.10.65 | 192.168.10.94 | 192.168.10.95 | 255.255.255.224 | 30 |
| Guests | 10 | /28 | 192.168.10.96 | 192.168.10.97 | 192.168.10.110 | 192.168.10.111 | 255.255.255.240 | 14 |
| WAN link | 2 | /30 | 192.168.10.112 | 192.168.10.113 | 192.168.10.114 | 192.168.10.115 | 255.255.255.252 | 2 |
Largest blocks are placed first so every block is aligned. Parent network 192.168.10.0/24. Unallocated: 140 addresses from 192.168.10.116.