Networking
What is CIDR?
Classless Inter-Domain Routing — a method for allocating IP addresses and routing using variable-length subnet masking.
CIDR (Classless Inter-Domain Routing) is an IP addressing scheme that replaced the old class-based system. It uses a suffix notation (e.g., 192.168.1.0/24) where the number after the slash indicates how many bits are the network portion.
CIDR allows more efficient allocation of IP addresses. A /24 network has 256 addresses (254 usable). A /16 has 65,536. A /8 has 16,777,216.
Common CIDR Blocks
- /32 — Single host (1 address)
- /24 — Typical LAN (256 addresses)
- /16 — Large network (65,536 addresses)
- /8 — Very large network (16.7M addresses)
- /0 — All addresses (default route)
FAQ
How do I calculate usable hosts from CIDR?
Usable hosts = 2^(32 - prefix length) - 2. For /24: 2^8 - 2 = 254 usable hosts. Use our Subnet Calculator to get full details instantly.
Related Terms