Calculate network address, broadcast, subnet mask, wildcard, and usable host range from any IPv4 + CIDR. Also flags RFC 1918 private ranges.

An IPv4 subnet is a contiguous block of addresses sharing a common prefix. CIDR notation (/24, /30, etc.) tells you how many leading bits define the network — everything after that is host space. The prefix length determines block size: each bit you add to the prefix halves the number of addresses, each bit you remove doubles it. CIDR replaced the old classful A/B/C model in 1993 (RFC 1519) so allocations could be sized to actual need instead of fixed octet boundaries.

The calculator's output reflects how a router sees the block. The network address is the first address (all host bits zero) and identifies the subnet itself — it's not assignable to a host. The broadcast address is the last address (all host bits one) and is reserved for the all-hosts broadcast. Everything between those two is the usable host range. So a /24 has 256 total addresses but only 254 usable. Two exceptions: /31 (RFC 3021, point-to-point links) and /32 (host route) use both addresses as usable.

The wildcard mask is the bitwise inverse of the subnet mask. You'll see it in Cisco ACL match statements and OSPF network area declarations, where the device wants to know which bits to ignore rather than which bits to match. If you're working with wildcards directly, the wildcard tool converts in either direction.

Worked example: for 192.168.1.0/24 you get 254 usable hosts (192.168.1.1–192.168.1.254), with 192.168.1.0 reserved as the network address and 192.168.1.255 as broadcast. The mask is 255.255.255.0, the wildcard is 0.0.0.255.

The calculator flags addresses inside the RFC 1918 private ranges: 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16. These are non-routable on the public internet and are what most internal networks use behind NAT. Anything else is treated as public address space.