Subnet calculator and VLSM designer
Plan IPv4 networks fast. Get the network address, broadcast, mask, host range, binary breakdown, and a full variable-length subnet plan, all in your browser.
Calculate a subnet or design a VLSM plan
192.168.1.0/24
32-Bit Binary Bitmask Breakdown
Every IPv4 address consists of 32 binary bits divided into 4 octets. The bitwise AND operation (IP AND Mask = Network) isolates the network ID from the host space:
Subnet Decomposition (Split /24 into 2x /25 Subnets)
Need to segment this network for guest isolation or separate VLANs? Borrowing 1 host bit divides 192.168.1.0/24 into two equal /25 subnets:
| Subnet CIDR | Usable Host Range | Broadcast Address | Usable Hosts | Action |
|---|---|---|---|---|
| 192.168.1.0/25 | 192.168.1.1 - 192.168.1.126 | 192.168.1.127 | 126 | |
| 192.168.1.128/25 | 192.168.1.129 - 192.168.1.254 | 192.168.1.255 | 126 |
Device CLI Configuration Generator
! Cisco IOS / Catalyst / Nexus Configuration ! VLAN Interface & DHCP Pool Definition interface Vlan100 description Purple-Managed Guest WiFi ip address 192.168.1.1 255.255.255.0 no shutdown exit ip dhcp excluded-address 192.168.1.1 ip dhcp pool GUEST_WIFI_POOL network 192.168.1.0 255.255.255.0 default-router 192.168.1.1 dns-server 1.1.1.1 8.8.8.8 lease 0 1 0 exit
Why subnetting still matters
Subnetting splits one IP range into smaller, isolated networks so you can separate guest, staff, and IoT traffic, control broadcast domains, and use address space efficiently. This calculator handles single-subnet maths, interactive binary bitmask visualization, device CLI configuration generation, and variable-length subnet masking (VLSM) for multi-segment designs.
What this tool gives you
- Network and broadcast addresses, subnet mask, wildcard mask, and usable host range for any CIDR prefix from /1 to /32.
- Interactive 32-bit binary bitmask visualizer showing network, subnet, and host bits in real time.
- A VLSM allocation plan that fits each subnet by required host count, largest first, with visual address space utilization and CLI export.
IPv4 CIDR Prefix, Subnet Mask, and Host Capacity Reference Table
Quick reference guide mapping CIDR prefix lengths (/1 to /32) to dotted-decimal subnet masks, wildcard masks, usable IP addresses, and common network engineering applications.
| CIDR | Subnet Mask | Wildcard Mask | Usable Hosts | Common Enterprise Use Case |
|---|---|---|---|---|
| /32 | 255.255.255.255 | 0.0.0.0 | 1 | Host route, loopback interface, single endpoint |
| /31 | 255.255.255.254 | 0.0.0.1 | 2 | Point-to-point router links (RFC 3021 standard) |
| /30 | 255.255.255.252 | 0.0.0.3 | 2 | Legacy point-to-point links (dedicated network/broadcast) |
| /29 | 255.255.255.248 | 0.0.0.7 | 6 | Small router links, firewall DMZ with static IPs |
| /28 | 255.255.255.240 | 0.0.0.15 | 14 | Server rack management subnet, lab environment |
| /27 | 255.255.255.224 | 0.0.0.31 | 30 | Small branch office, security camera / IoT VLAN |
| /26 | 255.255.255.192 | 0.0.0.63 | 62 | Departmental subnet (e.g. accounting, executives) |
| /25 | 255.255.255.128 | 0.0.0.127 | 126 | Medium department, secondary branch VLAN |
| /24 | 255.255.255.0 | 0.0.0.255 | 254 | Standard Class C LAN, default office subnet |
| /23 | 255.255.254.0 | 0.0.1.255 | 510 | Hotel guest WiFi, boutique venue, medium office |
| /22 | 255.255.252.0 | 0.0.3.255 | 1,022 | Corporate campus VLAN, medium venue guest WiFi |
| /21 | 255.255.248.0 | 0.0.7.255 | 2,046 | University student accommodation, large venue WiFi |
| /20 | 255.255.240.0 | 0.0.15.255 | 4,094 | Stadium, convention centre, airport guest WiFi scope |
| /19 | 255.255.224.0 | 0.0.31.255 | 8,190 | Metropolitan network, major transit hub infrastructure |
| /18 | 255.255.192.0 | 0.0.63.255 | 16,382 | Large enterprise site aggregation, regional network |
| /17 | 255.255.128.0 | 0.0.127.255 | 32,766 | Multi-campus enterprise block allocation |
| /16 | 255.255.0.0 | 0.0.255.255 | 65,534 | Standard Class B supernet, private cloud VPC |
| /12 | 255.240.0.0 | 0.15.255.255 | 1,048,574 | RFC 1918 172.16.0.0/12 private range block |
| /8 | 255.0.0.0 | 0.255.255.255 | 16,777,214 | RFC 1918 10.0.0.0/8 private major network block |
High-density WiFi subnetting and DHCP scope best practices
Designing IP subnets for wireless venues differs fundamentally from wired switching architectures. Wireless devices share physical RF airtime. When a device sends an Address Resolution Protocol (ARP) broadcast or multicast packet, the wireless access point must retransmit that frame at low base data rates across all associated radios.
1. Limit broadcast domain sizes
Never deploy large flat /16 networks (65,534 hosts) on guest SSIDs without client isolation. A /22 (1,022 hosts) or /23 (510 hosts) subnet provides sufficient lease room while preventing excessive multicast airtime consumption.
2. Tune DHCP lease durations
In transient environments like retail malls, cafes, and stadiums, set DHCP lease times to 30 to 60 minutes. Long 24-hour leases cause scope exhaustion as transient visitors retain IP leases long after leaving the venue.
3. Enable wireless client isolation
Enabling AP client isolation prevents peer-to-peer device traffic on public subnets, blocking internal network scanning and mitigating malicious ARP poisoning attacks.
For student accommodation, multi-dwelling units (MDUs), and build-to-rent (BTR) communities, traditional VLAN-per-user architectures exhaust switch VLAN tables (limited to 4,094 VLANs). Learn how Purple uses Identity Pre-Shared Keys (iPSK) and RADIUS-backed dynamic isolation to give every resident a private personal area network on a single shared SSID.
Download the high-density WiFi architecture & DHCP sizing guide
Get our reference architecture guide for multi-vendor campus networks. Includes DHCP scope sizing templates for Cisco Meraki, HPE Aruba, Ruckus, and Juniper Mist, plus VLAN security checklists.
Related network engineering tools and technical guides
Multi-Tenant iPSK Subnet Designer →
Design resident subnets and DHCP pools for student housing and BTR developments.
Access Point Calculator →
Calculate required AP density and client capacity across indoor and outdoor venue areas.
Captive Portal Guide →
Comprehensive architectural guide to guest onboarding, walled gardens, and RADIUS integration.
Enterprise WiFi Security Guide →
Deep dive into 802.1X, WPA3-Enterprise, certificate-based staff authentication, and network isolation.
Frequently asked questions about IP subnetting and CIDR
What is the difference between a subnet mask and CIDR notation?
A subnet mask is a 32-bit dotted-decimal number (e.g. 255.255.255.0) that separates the network portion of an IP address from the host portion. Classless Inter-Domain Routing (CIDR) notation represents the same mask as a slash followed by the count of consecutive leading binary 1s (e.g. /24). CIDR eliminated rigid Class A, B, and C boundaries to allow flexible network prefix lengths.
How do you calculate usable host addresses in an IPv4 subnet?
The formula for usable IPv4 hosts is 2^(32 - prefix) - 2. Two addresses are reserved by RFC standards: the first address (all host bits 0) is the Network ID, and the last address (all host bits 1) is the Directed Broadcast address. For example, a /24 subnet has 32 - 24 = 8 host bits, yielding 2^8 - 2 = 254 usable hosts. Point-to-point /31 subnets under RFC 3021 and single-host /32 loopbacks are exceptions that permit 2 and 1 usable addresses respectively.
What subnet size is recommended for guest WiFi and high-density venues?
For high-density guest WiFi environments like stadiums, hotels, and retail malls, a /22 subnet (1,022 usable leases) or /20 subnet (4,094 usable leases) is recommended alongside a short DHCP lease time (such as 30 to 60 minutes). This prevents DHCP scope exhaustion while client isolation prevents ARP broadcast storms across the wireless network.
What is Variable Length Subnet Masking (VLSM) and why is it used?
VLSM allows network engineers to divide an IP address block into subnets of varying sizes based on the specific host requirements of each segment (such as POS terminals, corporate workstations, guest WiFi, and router links). This avoids wasting address space compared to fixed-length subnetting.
Why should high-density WiFi networks avoid large flat /16 subnets?
Flat /16 subnets create enormous broadcast domains with up to 65,534 hosts. On wireless networks, broadcast and multicast frames (like ARP requests and mDNS) are transmitted at low legacy data rates across all access points, consuming airtime and degrading throughput. Segmenting into smaller /22 or /23 VLANs with AP client isolation maintains airtime efficiency.
How does Purple work with enterprise subnets and VLAN segmentation?
Purple integrates with your enterprise network infrastructure (Cisco Meraki, HPE Aruba, Ruckus, Juniper Mist, and Fortinet) to deliver cloud captive portals, dynamic VLAN steering via RADIUS, and resident-isolated iPSK networks without requiring hardware reconfiguration.
Planning a venue network?
Subnetting is the foundation. Purple layers guest onboarding, captive portals, and location analytics on top of the network you design here, across Cisco Meraki, HPE Aruba, Ruckus, and Juniper Mist.
Book a 20-min demoNetforge Network Multi-Tool
Run offline network health checks, path analysis, and latency diagnostic scans directly from your desktop.
Download Multi-Tool