CIDR Ranges for Firewall Rules
Convert IP ranges to CIDR notation for firewall allow/deny rules and ACLs.
IPv4 subnetting reference. /31 and /32 are handled per RFC 3021 (point-to-point and single-host). All math runs locally in your browser.
Firewall tips
Firewall and security-group rules use CIDR notation. Confirm a range covers exactly the IPs you intend — no more, no less.
The wildcard mask is what Cisco ACLs use (inverse of the subnet mask) — this tool shows both.
To allow a single host, use /32. To allow a whole office subnet, match its network CIDR exactly to avoid over-permitting.
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