What is CIDR and Subnetting?
CIDR (Classless Inter-Domain Routing, IETF RFC 4632) is an IP addressing methodology that replaced legacy Class A, B, and C networks. A CIDR notation (such as 192.168.1.0/24) combines an IP address with a slash suffix indicating the number of leading bits in the subnet mask.
Subnetting partitions a larger network into smaller, isolated routing domains to optimize traffic flow and enforce firewall security policies.
How to calculate CIDR subnets and extract IP lists
- Enter CIDR network notation. Type an IPv4 network address and prefix length (e.g. 192.168.1.0/24 or 10.0.0.0/16) into the input box.
- Click Calculate Subnet. The tool immediately computes the subnet boundaries, binary masks, and host capacities in browser memory.
- Inspect network parameters. Review the network ID, broadcast address, netmask, wildcard mask, and first/last usable IP addresses.
- Export the IP address list. Download the complete list of assignable IP addresses as a plain text or CSV file for firewall allowlists.
What network parameters are calculated?
- Network Address & Broadcast Address — The first and last boundary addresses in the subnet block.
- Subnet Mask & Wildcard Mask — Standard dotted-decimal representation (e.g.
255.255.255.0) and inverted wildcard mask for ACLs. - Usable IP Address Range — The exact assignable host range (excluding network and broadcast addresses).
- Host Capacities — Total theoretical address space vs actual usable host capacity.
- Complete Assignable IP Lists — Plain text or CSV export of every valid IP address in the CIDR block.
Supported IP standards and prefixes
Supports all IPv4 CIDR prefix lengths from /0 to /32, including RFC 1918 private subnets (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16) and public Internet address blocks.
Privacy and network security
Calculations occur 100% client-side inside your browser tab using bitwise arithmetic. Internal corporate network topologies, VPN IP ranges, and private subnets are never transmitted across the network.
Known limitations
To preserve browser responsiveness and prevent memory exhaustion, full IP list generation is limited to subnets of /16 (65,534 hosts) or smaller. Larger subnets provide full boundary and capacity calculations.
Common use cases
- Cloud & DevOps Engineering — Designing AWS VPC, Azure VNet, and GCP Subnet CIDR allocations.
- Firewall & Security Configuration — Generating IP allowlists for Cisco, pfSense, and AWS Security Groups.
- Network Administration — Planning DHCP pools, VLAN boundaries, and point-to-point router links (/31).
CIDR Extractor vs IP Address Extractor
The CIDR Extractor calculates subnet boundaries and generates IP address ranges from a prefix. If you want to extract unstructured IP addresses out of messy text or server logs, use our IP address extractor or log field extractor.
Frequently asked questions
What does /24 mean in CIDR notation?
A /24 prefix means the first 24 bits are dedicated to the network prefix, leaving 8 bits for hosts (256 total addresses, 254 usable hosts with subnet mask 255.255.255.0).
Why are there 2 unusable IP addresses in most subnets?
In standard IPv4 subnets, the very first address is reserved as the Network ID, and the last address is reserved as the Subnet Broadcast address.
What is a wildcard mask used for?
A wildcard mask is the bitwise inversion of a subnet mask (e.g. 0.0.0.255 for a /24), used by Cisco routers and Access Control Lists (ACLs) to match IP ranges.
Can I download all IP addresses in a CIDR block to CSV?
Yes. Clicking 'Download IP List (.csv)' exports all usable host addresses in sequential order ready for firewall importing.
Does EasyExtract log or track the subnets I calculate?
No. All CIDR bitwise arithmetic is performed 100% locally in your browser memory — nothing is ever sent to any server.