Subnet Mask Cheat Sheet
CIDR Calculator & IP Lookup Reference
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A web-based CIDR calculator and subnet mask cheat sheet for quick IP address reference.
- for
- Network engineers and anyone working with IPv4 subnetting.
- pricing
- free
Key features
- CIDR Table — Shows subnet mask, hex, total IPs, usable hosts, wildcard and class for every prefix /0-/32.
- VLSM Calculator — Helps compute variable-length subnet masks for efficient address allocation.
- IPv4-to-IPv6 Converter — Converts IPv4 addresses to their IPv6 representation.
- IP Check Tool — Validates an IP address and displays its class and private/public status.
- Wildcard Mask Lookup — Provides inverse masks for ACLs and routing protocols.
- /31 Exception Note — Documents the RFC 3021 rule where both addresses are usable for point-to-point links.
Use cases
- Determine the number of usable hosts for a given CIDR prefix.
- Find the correct wildcard mask for an ACL rule.
- Convert an IPv4 address to IPv6 format for documentation.
- Identify private IP ranges when designing internal networks.
- Quickly reference legacy classful address information.
Subnet Mask Cheat Sheet FAQ
What is CIDR notation?+
CIDR notation combines an IP address with a slash and a number indicating how many leading bits form the network prefix.
Why use /30 for point-to-point links?+
A /30 subnet provides exactly two usable host addresses, minimizing wasted IP space for router-to-router connections.
What is the difference between /24 and 255.255.255.0?+
There is none; /24 is the CIDR shorthand for the dotted-decimal mask 255.255.255.0.
How many usable hosts are in a /23?+
A /23 contains 512 total IPs, with 510 usable hosts after subtracting network and broadcast addresses.
What is a wildcard mask?+
A wildcard mask is the inverse of a subnet mask, used in ACLs and routing protocols to specify which bits to match.
Summarized by DevHunt from subnetmaskcheatsheet.com · Oct 6, 2026. Details may change; check the official site.
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