Network Subnet Calculator
Quick Reference
Common CIDR Notations
- /8 - 255.0.0.0 (16,777,214 hosts)
- /16 - 255.255.0.0 (65,534 hosts)
- /24 - 255.255.255.0 (254 hosts)
- /30 - 255.255.255.252 (2 hosts - point-to-point)
Private IP Ranges
- Class A: 10.0.0.0/8
- Class B: 172.16.0.0/12
- Class C: 192.168.0.0/16
Frequently Asked Questions
What is a subnet mask?
A subnet mask is a 32-bit number that divides an IP address into network and host portions. It determines which part of an IP address refers to the network and which part refers to the host. Subnet masks are essential for routing IP packets and organizing networks efficiently.
What does CIDR notation mean?
CIDR (Classless Inter-Domain Routing) notation is a compact representation of an IP address and its associated network mask. For example, 192.168.1.0/24 means the first 24 bits are the network portion, leaving 8 bits for hosts. The /24 is equivalent to subnet mask 255.255.255.0.
How do I calculate the number of usable hosts?
The formula is 2^(32-CIDR) - 2. For example, a /24 network has 2^8 = 256 total addresses, minus 2 (network and broadcast addresses) = 254 usable host addresses. The network address is always the first address, and the broadcast address is always the last address in the range.
What is a wildcard mask?
A wildcard mask is the inverse of a subnet mask, used primarily in access control lists (ACLs) on routers and firewalls. While subnet masks use 1s for the network portion, wildcard masks use 0s for the network portion and 1s for the host portion. For example, subnet mask 255.255.255.0 has wildcard mask 0.0.0.255.
What are private IP addresses?
Private IP addresses are reserved for use within private networks and cannot be routed on the public internet. The three private IP ranges are: 10.0.0.0/8 (Class A), 172.16.0.0/12 (Class B), and 192.168.0.0/16 (Class C). These addresses can be freely used within organizations without requiring registration.
What is the difference between network address and broadcast address?
The network address is the first address in a subnet and identifies the network itself - it cannot be assigned to a host. The broadcast address is the last address in a subnet and is used to send data to all hosts on that network simultaneously. Both addresses are reserved and cannot be assigned to individual devices.