Split, join, and plan IPv4 and IPv6 subnets with cloud mode support for AWS, Azure, GCP, and OCI.
| Subnet | Mask / Wildcard | Address Range | Usable Range | Hosts | Reverse DNS | Note | Actions |
|---|---|---|---|---|---|---|---|
10.0.0.0/16 Private | 255.255.0.0 0.0.255.255 | 10.0.0.0 - 10.0.255.255 | 10.0.0.1 - 10.0.255.254 | 65,534 | 0.10.in-addr.arpa | + note |
Full calculation for 32-bit and 128-bit networks: subnet mask, wildcard, address type, and reverse DNS. Switch protocols with one click.
Interactively divide and merge subnets. Build complex designs with full undo/redo history.
Specify host requirements, get optimally-sized subnets. See utilization, waste, and free space.
CSV, Excel, JSON, clipboard copy, and shareable URLs. Import previous designs from JSON.
Guides on subnetting, CIDR notation, VLSM, IPv6, the cheat sheet, and a practice quiz.
A subnet calculator divides IP networks into smaller subnetworks. Enter a network address and prefix length (like 192.168.1.0/24) to see the address range, usable hosts, subnet mask, and broadcast address. PrefixBench supports IPv4, IPv6, VLSM planning, and cloud provider modes.
A /24 has 256 total addresses and 254 usable hosts (network and broadcast are reserved). Cloud providers reserve more: AWS 5 (251 usable), Azure 5 (251 usable), GCP 4 (252 usable), OCI 3 (253 usable).
VLSM (Variable Length Subnet Masking) creates subnets of different sizes from one network. Specify how many hosts each subnet needs, and VLSM assigns the smallest matching prefix to minimize waste.
IPv6 uses 128-bit addresses with a much larger address space. Every subnet is conventionally /64 (2^64 addresses). There are no reserved network or broadcast addresses, so all addresses are usable.
AWS reserves 5 IPs: network address (.0), VPC router (.1), DNS server (.2), reserved for future use (.3), and broadcast (.255 in a /24). A /24 in AWS has 251 usable IPs.