VLSM Calculator View on GitHub

IPv4 network planning

Plan subnets without the guesswork.

Enter a parent CIDR and the hosts each subnet needs. The calculator allocates efficient, non-overlapping blocks from largest to smallest.

01 / Network plan

Define your address space

IPv4 address with CIDR prefix
Shown separately from the host range.

Subnet requirements

Use the number of assignable host addresses each subnet needs.

Subnet name VLAN ID Required hosts
Output columns

Saved in this browser for 90 days.

Network utilities CIDR overlap checker and route summarisation

Network utility

CIDR overlap checker

Compare two IPv4 CIDR blocks, including `/31` and `/32` ranges.

Network utility

Route summarisation

Aggregate IPv4 CIDRs without including addresses outside the supplied routes.

Enter one CIDR per line, or separate routes with commas or spaces.