Enter an IPv4 block in CIDR notation to get the network, broadcast, netmask, wildcard, usable host range, and total IP count. Free — runs entirely in your browser, no signup.
CIDR (Classless Inter-Domain Routing) writes an IP range as an address plus a prefix length, like 192.168.1.0/24. The prefix (/24) says how many leading bits are fixed as the network; the remaining bits are host addresses. A smaller prefix covers more IPs: a /24 is 256 addresses, a /16 is 65,536, and a /32 is a single host.
This calculator is handy when you are building firewall rules or reviewing an External Dynamic List (EDL), because blocklists are published as CIDR ranges so one line can cover a whole block of attacker IPs.
The network address is the first IP in the block (all host bits 0); the broadcast is the last (all host bits 1). Neither is assignable to a host on a normal subnet, which is why usable hosts = total − 2 for /30 and larger.
The netmask (255.255.255.0) marks network bits; the wildcard mask (0.0.0.255) is its inverse and marks host bits. Most firewalls use netmasks; Cisco ACLs use wildcard masks.
Firewalls expand CIDR ranges automatically, so a feed can block thousands of IPs per line. The best IP blocklists ship as compact CIDR ranges rather than giant flat IP lists.
ThreatListPro's blocklist is ~1,600 CIDR ranges (4M+ IPs) curated from real brute-force attacks observed on production Palo Alto firewalls — ready to paste into your firewall's EDL.
Stop hand-calculating and hand-entering ranges. ThreatListPro delivers ~1,600 curated attacker CIDR blocks as one EDL URL — 5-minute setup, automatic updates.
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