Subnet / CIDR Visualizer
Visualize and break down any IPv4 CIDR block. See network address, broadcast, host range, mask, wildcard, and a bit-by-bit binary view of where the network ends and the host bits begin. Split a block into smaller subnets in one click.
How to Use
- Type a CIDR block (e.g., <code>192.168.1.0/24</code>, <code>10.0.0.0/8</code>) or pick a preset.
- The Network Info panel shows network address, broadcast, first/last usable host, total addresses, and standard masks.
- The Binary panel renders all 32 bits with the network/host boundary highlighted — easy to see the prefix at a glance.
- Use the "Split into" dropdown to break the block into smaller equal-size subnets (e.g., a /24 into four /26s).
- Click any output value to copy it to your clipboard.
- Everything runs in your browser — no values transmitted.
Formulas & Concepts
A Brief History of CIDR
Before 1993, IP networks were assigned in three rigid sizes: Class A (/8, 16M addresses), Class B (/16, 65K), and Class C (/24, 254). Most organizations needed something between a Class B and a Class C — and a Class B was always granted, even when only a few hundred IPs were needed. By the late 1980s the IPv4 address space was being burned through far faster than population growth justified, with most Class B blocks used at less than 1% capacity.
Classless Inter-Domain Routing (CIDR), defined in RFC 1517–1519 (1993), replaced the fixed classes with flexible prefix lengths. An organization could now request /22 (1024 addresses) instead of being forced to take a /16 (65,536). Routers could aggregate multiple consecutive prefixes into a single advertisement, dramatically reducing the size of the global routing table. CIDR is widely credited with extending the useful lifetime of IPv4 by 15+ years and is the reason we're still functioning on a 32-bit address space in 2026.
The visualization in this tool — showing where the network bits end and host bits begin — is exactly what made CIDR comprehensible. The Class system hid this boundary; CIDR exposes it as a single number after a slash.
About This Visualizer
This tool parses CIDR notation, computes network/broadcast/host range using bitwise operations, and visualizes all 32 bits with the network-vs-host boundary highlighted. The subnet splitter halves the block at each step (a /24 → two /25s, four /26s, eight /27s, etc.) and shows every resulting subnet's range.
Everything runs in your browser using JavaScript's bitwise operators on unsigned 32-bit integers. No values are transmitted. For IPv6 (which uses 128-bit addresses and different conventions), see the IPv4 ↔ IPv6 Converter.
Frequently Asked Questions
What is CIDR notation?
Classless Inter-Domain Routing notation: <code>192.168.1.0/24</code> means 'the network whose address starts with the first 24 bits of 192.168.1.0.' The number after the slash (the prefix length) tells you how many bits are the network portion; the remaining bits identify hosts within the network. CIDR replaced the older Class A/B/C system in 1993 and is universal now.
What's the difference between network address, broadcast, and host range?
<strong>Network address</strong> — the lowest address in the block, identifies the network itself (e.g., 192.168.1.0). <strong>Broadcast address</strong> — the highest address, used to send to all hosts at once (e.g., 192.168.1.255). <strong>Host range</strong> — the addresses in between, assignable to actual devices (192.168.1.1 to 192.168.1.254 on a /24).
Why does a /24 only have 254 hosts, not 256?
256 addresses total = 254 hosts + network address (.0) + broadcast (.255). The network and broadcast addresses can't be assigned to actual hosts. Exception: /31 (used for point-to-point links per RFC 3021) and /32 (single host) use all addresses with no broadcast.
What's a wildcard mask?
The bitwise inverse of the subnet mask. For /24 the subnet mask is 255.255.255.0; the wildcard mask is 0.0.0.255. Cisco ACLs and OSPF area definitions use wildcard masks instead of subnet masks. The pattern is the same — they just specify which bits to ignore rather than which to match.
How do I split a /24 into smaller subnets?
Each step up in prefix halves the address space. /24 (256 addr) → two /25s (128 addr each) → four /26s (64 each) → eight /27s (32 each) → sixteen /28s (16 each). Use the 'Split into' selector to see exactly which subnets you get.
Does this support IPv6?
This visualizer focuses on IPv4. For IPv6 prefix and address conversion, see the IPv4 ↔ IPv6 Converter tool. The math is similar but with 128-bit addresses and different size conventions (typical home network is /60 or /56, not /24).
What's a /31 used for?
Point-to-point links between two routers (RFC 3021). With only 2 addresses and no broadcast/network, both can be assigned. Saves IPs on backbone links. /30 (4 addresses, 2 usable) was the traditional choice but uses twice as many addresses for the same purpose.
Are private IP ranges flagged?
The tool detects RFC 1918 private ranges (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16), loopback (127.0.0.0/8), link-local (169.254.0.0/16), and CGNAT (100.64.0.0/10). Public addresses are flagged as such.
Common Use Cases
Network design and planning
Plan subnets for a new office or VPC — start with a /16 or /20 and split into VLAN-sized blocks.
CCNA / Network+ studies
See subnetting math made visual — useful for learning the binary mechanics of network/host boundary.
Firewall rule writing
Compute exact wildcard masks for ACLs, network address for routing entries, and host ranges for explicit firewall rules.
Cloud VPC configuration
Design AWS/GCP/Azure VPC CIDR blocks with proper subnet sizing for public/private/database tiers.
Documentation diagrams
Generate accurate IP range descriptions for network diagrams and runbooks.
IP allocation auditing
Verify reported subnet boundaries match what's actually configured on routers and DHCP scopes.
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