How to use the cidr table lookup
- Look up any CIDR prefix from /0 to /32 to see its subnet mask, usable hosts, and block size.
- Click any row to copy the mask or wildcard to your clipboard.
- Bookmark for quick reference during ACL or VLAN planning.
CIDR Table Lookup
Masks and host counts
Matching Prefix—
Subnet Mask—
Wildcard Mask—
Total IPs—
Usable Hosts—
Full CIDR Table
| CIDR | Subnet Mask | Wildcard | Total IPs | Usable Hosts |
|---|
Frequently asked questions
What is the subnet mask for /24?
/24 maps to 255.255.255.0 — eight host bits, 254 usable hosts per subnet. The classic 'Class C' size.
How many hosts fit in a /23?
A /23 has 9 host bits = 512 addresses, 510 usable. Two contiguous /24s aggregated into one larger subnet.
Why is /31 special in modern networks?
/31 follows RFC 3021: both of its 2 addresses are usable, saving two addresses on every point-to-point link.
What is the wildcard mask for /25?
/25 = 255.255.255.128. Its wildcard is the inverse: 0.0.0.127.