Network Intelligence
Free online Subnet & CIDR Calculator: calculate network address, broadcast IP, usable host range, wildcard mask, and binary subnet masks with instant Nmap scan command generation.
A Subnet Calculator is an essential networking and cybersecurity utility that computes network boundaries, host capacity, broadcast addresses, and netmasks for any given IPv4 address and CIDR prefix. Classless Inter-Domain Routing (CIDR) replaced the legacy Class A, B, and C addressing scheme with variable-length prefix notation (e.g. /24, /16, /22). Calculating these boundaries accurately is vital for network segmentation, firewall ACL definitions, VPC planning, and scoping penetration tests.
For ethical hackers and security researchers, understanding CIDR notation is directly tied to target scoping and discovery scanning. Tools like Nmap, Masscan, and ZMap require network specifications in CIDR notation (such as 192.168.1.0/24 or 10.0.0.0/16). Knowing the exact first and last usable host IPs prevents out-of-scope scanning and ensures complete coverage of authorized targets.
This online Subnet Calculator operates entirely client-side inside your browser, ensuring maximum privacy and zero latency. It instantly calculates network addresses, broadcast IPs, usable host ranges, binary masks, wildcard masks, and even generates ready-to-use Nmap commands for network reconnaissance.
An IPv4 address consists of 32 bits divided into four 8-bit octets separated by dots. A subnet mask divides those 32 bits into two parts: network bits (represented by 1s) and host bits (represented by 0s). The CIDR prefix (e.g. /24) indicates the number of continuous 1s in the netmask.
To calculate the Network Address, a bitwise AND operation is performed between the 32-bit IP integer and the 32-bit subnet mask integer. The Broadcast Address is determined by a bitwise OR between the Network Address and the bitwise NOT of the subnet mask (the wildcard mask). The usable host range spans from Network Address + 1 to Broadcast Address - 1.
The total number of IP addresses in any subnet is 2^(32 - prefix). For traditional subnets (/30 and larger), 2 addresses are reserved for the network ID and broadcast address, leaving 2^(32 - prefix) - 2 usable host addresses. Special RFC 3021 subnets (/31) allow 2 usable hosts on point-to-point links, while /32 specifies a single host.
Different CIDR prefixes cater to different scales of network architecture. A /24 subnet provides 254 usable hosts (common for home LANs and branch offices). A /16 subnet provides 65,534 usable hosts (typical for corporate campuses or large cloud VPCs). A /8 subnet spans 16,777,214 addresses.
Micro-segmentation often leverages /27 (30 hosts), /28 (14 hosts), or /29 (6 hosts) for isolating database tiers, management interfaces, or DMZ jump hosts. Point-to-point router links typically use /30 (2 usable hosts) or /31.
In penetration testing, specifying the right CIDR block is critical. Running an aggressive Nmap service scan across an entire /16 takes hours and may crash intermediate routers, whereas targeting specific /24 or /27 subnets yields faster, more actionable reconnaissance data.
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