| CIDR | Subnet Mask | Usable Hosts |
|---|
How to Read This CIDR Chart
Each row shows a CIDR prefix length from /0 (the entire IPv4 space) to /32 (a single host). The subnet mask column shows the dotted-decimal equivalent, usable hosts subtracts the network and broadcast addresses, and the wildcard mask is the bitwise inverse used in ACLs and routing protocols like OSPF.
Common prefixes in practice: /24 is the standard for most local networks (254 hosts), /16 for large organisations (65,534 hosts), and /30 or /29 for point-to-point links between routers (2 or 6 usable addresses).
Choosing the Right Prefix
The /24 subnet is the most widely used in office and home networks because it provides 254 usable host addresses—enough for most LANs while keeping broadcast domains manageable. For cloud VPCs, AWS and Azure default to /16 for the VPC and /24 for subnets. Point-to-point links between routers typically use /30 (2 usable IPs) or /31 (2 usable IPs, no broadcast) when supported.
For data centre designs with many VLANs, you might split a /24 into four /26 subnets (62 hosts each) or two /25 subnets (126 hosts each) depending on your rack density.