
Subnet & CIDR Calculator
Calculate usable host allocations, subnet masks, wildcard masks, network and broadcast addresses, and inspect real-time 32-bit binary octet bit-splitting for enterprise IPv4 networking.
Subnet & CIDR Tactical Calculator
Real-time IPv4 Variable Length Subnet Masking (VLSM) engine. Compute network boundaries, usable IP ranges, wildcard masks, and inspect exact 32-bit binary bit-splitter boundaries.
Network Classification
Calculated Tactical Boundaries
254 Usable Hosts32-Bit Binary Bit-Splitter Architecture
IPv4 CIDR & Subnet Mask Quick Reference Table
Standard CIDR prefix lengths, corresponding subnet masks, wildcard masks, and maximum assignable host counts.
| CIDR Prefix | Subnet Mask | Wildcard Mask | Usable Hosts | Common Deployment |
|---|---|---|---|---|
| /8 | 255.0.0.0 | 0.255.255.255 | 16,777,214 | Class A Default |
| /16 | 255.255.0.0 | 0.0.255.255 | 65,534 | Class B Default |
| /20 | 255.255.240.0 | 0.0.15.255 | 4,094 | Mid Enterprise |
| /22 | 255.255.252.0 | 0.0.3.255 | 1,022 | Branch Site |
| /24 | 255.255.255.0 | 0.0.0.255 | 254 | Standard LAN (Class C) |
| /25 | 255.255.255.128 | 0.0.0.127 | 126 | Split Subnet |
| /26 | 255.255.255.192 | 0.0.0.63 | 62 | Quarter Subnet |
| /27 | 255.255.255.224 | 0.0.0.31 | 30 | Department VLAN |
| /28 | 255.255.255.240 | 0.0.0.15 | 14 | Security DMZ / WAF |
| /29 | 255.255.255.248 | 0.0.0.7 | 6 | Small Server Farm |
| /30 | 255.255.255.252 | 0.0.0.3 | 2 | Router P2P Link |
| /31 | 255.255.255.254 | 0.0.0.1 | 2 | RFC 3021 Point-to-Point |
| /32 | 255.255.255.255 | 0.0.0.0 | 1 | Single Host Route |
16,777,214 usable host addresses. Used primarily for enterprise core backbones and cloud VPC architectures.
1,048,574 usable host addresses. Ideal for corporate branches, security zones, and multi-tier subnets.
65,534 usable host addresses. Default standard for home routers, SOHO labs, and micro-segmentation.
Understanding Subnetting & CIDR Mechanics
Why do we subtract 2 from the total host count?
In every standard IPv4 subnet, two host addresses are reserved by the TCP/IP protocol stack: the very first address (all host bits set to 0) identifies the Network itself, while the very last address (all host bits set to 1) is the Directed Broadcast address used to reach all devices in that subnet simultaneously.
What is Variable Length Subnet Masking (VLSM)?
VLSM allows network architects to divide an IP address space into subnets of varying sizes based on individual host requirements, rather than using a single uniform subnet mask. For example, a WAN serial link can be allocated a /30 (2 usable hosts), while a campus user VLAN receives a /23 (510 usable hosts), eliminating IP address wastage.
How does the Wildcard Mask work in Cisco IOS?
The wildcard mask is used in Cisco Access Control Lists (ACLs) and OSPF network statements. In binary, a 0 means "match this bit exactly", while a 1 means "ignore this bit / wildcard". It is calculated by subtracting the subnet mask from 255.255.255.255.