Why does /31 have 2 usable hosts but /24 has 254?

RFC 3021 reserves the network and broadcast addresses for /0 through /30, leaving `size - 2` usable. /31 and /32 are special: /31 is used for point-to-point links where both addresses are usable, and /32 is a single host.

Why is there an output limit?

A /16 is 65,536 IPs, /8 is 16,777,216. Rendering them all into the DOM would freeze your browser. The summary still computes the totals correctly; the list is just truncated for display.

IP Range Expander

Two modes in one tool. CIDR mode takes `192.168.1.0/24` and returns the network address, broadcast, first/last usable host, subnet mask, wildcard mask, and the full IP list (up to your configured limit so the browser doesn't melt on a /16). Range mode takes a start and end IP and decomposes it into the fewest possible CIDR blocks that cover exactly that range — useful for firewall rules, ACLs, and route tables that only accept CIDR. Everything runs locally, no DNS lookups, no network requests.

—

ModeCIDR block

Max IPs to listOutput format

Summary

Network: 192.168.1.0/29
Broadcast: 192.168.1.7
First usable: 192.168.1.1
Last usable: 192.168.1.6
Subnet mask: 255.255.255.248
Wildcard mask: 0.0.0.7
Total addresses: 8
Usable hosts: 6

IPs (8)

192.168.1.0
192.168.1.1
192.168.1.2
192.168.1.3
192.168.1.4
192.168.1.5
192.168.1.6
192.168.1.7

All math runs locally. No DNS lookups, no network requests.

How to use

Pick CIDR mode for `network/prefix` input, or Range mode for `start - end`.
Adjust the limit if you want more (or fewer) IPs listed. The summary always shows totals regardless.
Copy the IP list or the CIDR aggregation in your preferred format (lines, comma, or nmap-style space-separated).

Frequently asked questions

Why does /31 have 2 usable hosts but /24 has 254?: RFC 3021 reserves the network and broadcast addresses for /0 through /30, leaving `size - 2` usable. /31 and /32 are special: /31 is used for point-to-point links where both addresses are usable, and /32 is a single host.
Why is there an output limit?: A /16 is 65,536 IPs, /8 is 16,777,216. Rendering them all into the DOM would freeze your browser. The summary still computes the totals correctly; the list is just truncated for display.

Guides on this topic

IP Addresses and Subnets, Without the Hand-Waving What an IP address really is, how to read CIDR notation and count the hosts in a prefix, which ranges must never be routed, how IPv6 changes the arithmetic, and why sorting addresses as text goes wrong.

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