ectoplasma.orgCIDR Calculator
Enter an IPv4 address with CIDR prefix or subnet mask to calculate network details.
| CIDR Notation | - |
| IP Address | - |
| Subnet Mask | - |
| Wildcard Mask | - |
| Network Address | - |
| Broadcast Address | - |
| First Usable Host | - |
| Last Usable Host | - |
| Total Hosts | - |
| Usable Hosts | - |
| IP Class | - |
| Binary Mask | - |
What is CIDR notation?
CIDR (Classless Inter-Domain Routing) is a method of allocating IP addresses and routing IP packets. Introduced in 1993 to replace the older classful addressing system, CIDR uses a suffix notation — a forward slash followed by a number — to indicate how many bits of the IP address form the network prefix. For example, 192.168.1.0/24 means the first 24 bits identify the network, leaving 8 bits for host addresses within that network.
Subnet masks and wildcard masks
A subnet mask is a 32-bit number that separates an IP address into its network and host portions. A /24 prefix corresponds to a subnet mask of 255.255.255.0. The wildcard mask is the bitwise inverse of the subnet mask — for /24, that is 0.0.0.255. Wildcard masks are used in access control lists on routers and firewalls to match ranges of addresses. Understanding both representations is essential for configuring network equipment correctly.
How subnetting works
Subnetting divides a larger network into smaller, more manageable segments. A company with a /16 allocation (65,534 usable hosts) might split it into 256 /24 subnets of 254 usable hosts each, one per department or floor. This reduces broadcast traffic, improves security through isolation, and makes IP address management more structured. The network address (all host bits set to zero) identifies the subnet itself, while the broadcast address (all host bits set to one) reaches every device on that subnet.
Common prefix lengths
/32 is a single host. /31 is used for point-to-point links (RFC 3021). /30 provides two usable addresses, ideal for router-to-router connections. /24 is the most common subnet for local networks, giving 254 usable hosts. /16 provides 65,534 hosts and is typical for medium organisations. /8 covers over 16 million addresses and corresponds to the old Class A networks. Cloud providers commonly use /20 or /22 blocks for virtual private cloud subnets.
Privacy
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