Calculate. Understand. Design better networks.
Enter an IPv4 address and CIDR prefix and Subnetter breaks down the subnet completely — every address, the binary boundary, and what the subnet is actually used for in real network design.
Binary breakdown
Network layout
Subnet planning table
Subnet & CIDR details
What this subnet is for
Not sure what CIDR you need?
Common subnetting questions
What is CIDR notation?
CIDR notation writes a subnet mask as a slash followed by the number of network bits — e.g. /24 means the first 24 bits identify the network and the remaining 8 bits identify hosts.
How do you calculate the network address?
Bitwise AND the IP address with the subnet mask. Every host bit becomes 0, leaving only the network portion — that's what the Network layout panel above shows visually.
Why does a /24 only give 254 usable hosts, not 256?
The first address is the network address and the last is the broadcast address — both are reserved. The exceptions are /31 (both addresses usable, RFC 3021 point-to-point links) and /32 (a single host route).
What's a wildcard mask used for?
It's the bitwise inverse of the subnet mask, mainly seen in Cisco access control lists and OSPF network statements — a 0 bit means match exactly, a 1 bit means "don't care".
What is VLSM and when do I need it?
Variable Length Subnet Masking splits one base network into differently-sized subnets instead of equal blocks — useful when segments need very different host counts. Try the VLSM Planner.