Subnet Divider
Split a CIDR block into 2ⁿ equal subnets.
Overview
The subnet divider splits a CIDR block into 2^n equal child subnets. Give it a parent block like 10.0.0.0/16 and a target prefix length (say /20), and it returns every child CIDR in order — first network, last network, count, and the number of hosts in each.
Cloud architects carving a VPC into per-AZ subnets, network engineers planning a multi-VLAN deployment, and instructors building subnetting exercises all need a deterministic CIDR splitter. Long-tail keywords covered: split CIDR block into equal subnets, divide /16 into /24 list, and VPC subnet planning helper.
How it works
A CIDR with prefix length P splits into 2^(C-P) subnets at child prefix C. The new subnets are aligned on the next-deeper bit boundary — every child has the same number of addresses, and together they tile the parent exactly. The math is simple bit shifts: child i starts at parent_network + i * (2^(32-C)) for IPv4.
The tool also reports usable-host counts per child (network and broadcast addresses subtracted, except for /31 and /32), the total address count, and the parent's leftover capacity if you provide a child count that does not consume the full space.
Examples
10.0.0.0/16divided into/20→ 16 subnets:10.0.0.0/20,10.0.16.0/20, …,10.0.240.0/20.192.168.0.0/24divided into/26→ 4 subnets:192.168.0.0/26,192.168.0.64/26,192.168.0.128/26,192.168.0.192/26.10.0.0.0/22divided into/30→ 256 subnets, each with 2 usable hosts (/30reserves network and broadcast).- A
/24divided into/24→ one subnet identical to the parent, useful as a sanity check.
FAQ
Can I split into unequal subnets?
Not with this tool — every output is the same size. For variable-length subnet masking, split into the smallest size you need and combine adjacent blocks with the Subnet Aggregator if needed.
What is the smallest practical child prefix?
/30 for traditional point-to-point links (2 usable hosts), /31 per RFC 3021 if your equipment supports it (2 hosts, no broadcast reserved), /32 for single-host routes.
Why does the host count exclude two addresses on most prefixes?
Network and broadcast addresses are reserved per RFC. The exceptions are /31 (point-to-point) and /32 (single host).
Can I divide IPv6?
The divider focuses on IPv4 today. IPv6 splitting follows the same algorithm conceptually — pick a deeper prefix and tile — but the host-count column is rarely useful since every IPv6 subnet has 2^64 addresses or more.