IP Subnet & CIDR Calculator
Calculate subnet masks, wildcard masks, usable IP ranges, and CIDR blocks client-side instantly.
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Frequently Asked Questions
What is CIDR notation?
CIDR (Classless Inter-Domain Routing) notation is a compact representation of an IP address and its associated routing prefix. It appends a slash followed by the prefix length in bits (e.g., /24 represents a subnet mask with 24 active bits).
Why are the first and last IP addresses excluded?
In a standard IP network, the first address is reserved for the Network ID (identifying the subnet itself), and the last address is reserved for the Broadcast ID (used to send packets to all devices on the subnet). They cannot be assigned to hosts.
What are /31 and /32 subnets used for?
A /31 subnet has only 2 IP addresses and is used for point-to-point links between routers (RFC 3021). A /32 subnet represents a single host IP address (often used for loopback configurations).