Subnet Monkey

SubnetMonkey is a free tool for planning and documenting IP address space. Enter a CIDR block, split it into smaller subnets, assign VLANs and metadata, and export a clean network plan.

Key Features

Subnet Calculator
Enter an IPv4 or IPv6 CIDR block and instantly see the network address, broadcast, usable host range, subnet mask, wildcard mask, and more.

Split, Merge & Collapse
Break networks into smaller subnets or merge them back together with one click.

VLSM Auto-Allocator
Automatically allocate subnet space based on host requirements.

Conflict Checker
Quickly detect overlapping subnets before they cause problems in production.

Planning Table
Edit VLAN IDs, names, gateways, site information, and notes in a spreadsheet-style interface.

Export Tools
Export your network plans to JSON, CSV, or a shareable HTML report.

Quick Start Guide

Enter a CIDR block like 192.168.1.0/24.
Split subnets and assign VLAN information.
Export your network plan to CSV or HTML.