What is CIDR notation?

CIDR (Classless Inter-Domain Routing) notation is a compact way to represent an IP address and its associated network mask. For example, 192.168.1.0/24 means the first 24 bits are the network portion, leaving 8 bits for host addresses (256 total addresses, 254 usable).

How do I calculate the number of hosts in a CIDR range?

For IPv4, the formula is 2^(32 - prefix length). A /24 gives 2^8 = 256 total addresses. Subtract 2 for the network and broadcast addresses to get 254 usable host addresses. A /16 gives 65,536 total addresses (65,534 usable).

What is the difference between a subnet mask and a wildcard mask?

A subnet mask marks the network bits with 1s and host bits with 0s (e.g., 255.255.255.0 for /24). A wildcard mask is the inverse — host bits are 1s and network bits are 0s (e.g., 0.0.0.255 for /24). Wildcard masks are commonly used in ACLs and routing configurations.

Does this tool support IPv6 CIDR ranges?

Yes! This tool supports both IPv4 and IPv6 CIDR notation. Enter an IPv6 CIDR like 2001:db8::/32 to see the full network details including the expanded address, prefix information, and network boundaries.

Can I check if a specific IP address belongs to a CIDR range?

Yes. Use the IP Lookup tab to enter an IP address and one or more CIDR ranges. The tool will instantly tell you which ranges contain that IP address, making it easy to verify firewall rules, ACLs, or routing tables.

Free Online CIDR Range Expander & Subnet Calculator (No Signup) – FreeWWW

🌐 CIDR Range Expander

Expand CIDR ranges, calculate subnets, check IP membership, compare networks, split subnets, and visualize address space. Supports IPv4 and IPv6.

Check IP Membership

Enter an IP address and one or more CIDR ranges to check if the IP falls within them.

Compare Networks

Enter multiple CIDR ranges to compare side by side. Also checks for overlaps.

Split Subnet

Split a CIDR range into smaller subnets.

Aggregate / Summarize

Find the smallest CIDR that contains all given IPs or ranges.

IPv4 CIDR Cheat Sheet

Quick reference for all IPv4 prefix lengths.

Common Private Ranges

IPv6 Quick Reference

Recent Lookups

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