What is CIDR notation?

CIDR (Classless Inter-Domain Routing) notation represents an IP address and its associated network prefix. For example, 192.168.1.0/24 means the first 24 bits are the network part, leaving 8 bits for host addresses — giving 256 total addresses (254 usable).

How many hosts does a /24 subnet have?

A /24 subnet (subnet mask 255.255.255.0) has 256 total IP addresses, of which 254 are usable for hosts. The first address is the network address and the last is the broadcast address.

What is a subnet mask?

A subnet mask is a 32-bit number that divides an IP address into network and host portions. Written as 255.255.255.0 (decimal) or /24 (CIDR), it tells routers and hosts which part of an IP address identifies the network.

CIDR & IP Ranges

Subnet Calculator

Enter any IP with CIDR prefix or subnet mask — get network, broadcast, range, host count, and more.

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Subnet Calculator — CIDR, Masks, and IP Ranges Explained

Subnetting divides a network into smaller, more manageable pieces. A subnet calculator takes a CIDR block like 192.168.1.0/24 and instantly computes the network address, broadcast, usable range, and host count — essential for network planning.

CIDR Notation

CIDR (Classless Inter-Domain Routing) notation combines an IP address with a prefix length: 10.0.0.0/8. The prefix length (0–32) indicates how many bits are used for the network. A /24 has 256 addresses; a /16 has 65,536; a /8 has 16,777,216.

Network vs Broadcast Address

The first address in any subnet is the network address (cannot be assigned to a host). The last address is the broadcast address (sent to all hosts in the subnet). Everything in between is usable — so a /24 gives 254 usable host addresses.

Private IP Ranges (RFC 1918)

Three ranges are reserved for private networks: 10.0.0.0/8 (Class A, ~16M addresses), 172.16.0.0/12 (Class B, ~1M addresses), and 192.168.0.0/16 (Class C, ~65K addresses). These cannot be routed on the public internet.

Wildcard Masks

A wildcard mask is the inverse of a subnet mask, used in access control lists (ACLs) and OSPF. 0.0.0.255 is the wildcard for a /24 subnet, meaning the last octet can be any value.