Subnet Calculator
Calculate network details from IP and CIDR or subnet mask.
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Frequently Asked Questions
What is CIDR notation? +
CIDR (Classless Inter-Domain Routing) notation uses a slash followed by a number (like /24) to indicate how many bits are used for the network portion of the address. /24 means the first 24 bits are the network, leaving 8 bits (256 addresses) for hosts.
How many usable hosts does a subnet have? +
A subnet has 2^(32-CIDR) - 2 usable hosts. The subtracted 2 accounts for the network address (first) and broadcast address (last), which cannot be assigned to devices. A /24 has 254 usable hosts.
What is a wildcard mask and when is it used? +
A wildcard mask is the inverse of a subnet mask. Where the subnet mask has 1s, the wildcard has 0s. It is commonly used in Cisco ACLs and OSPF configurations to match ranges of IP addresses.
What is the difference between /31 and /32 subnets? +
A /32 is a single host address with no network or broadcast. A /31 has exactly 2 addresses and is used for point-to-point links between routers (RFC 3021), where neither address is wasted on broadcast.
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