Subnet Calculator: IPv4, IPv6, VLSM & Wildcard

Take the IP address and the prefix length (for example 192.168.1.10/24). The prefix tells you how many leading bits are the network part; the rest are host bits. The network address is the IP with every host bit set to 0, and the broadcast address is the IP with every host bit set to 1. Everything between those two is usable for devices. Enter the address above and the calculator does it instantly, including the mask and wildcard.

They are exact opposites. A subnet mask uses 1s for the network bits and 0s for the host bits: /24 is 255.255.255.0. A wildcard mask inverts that, using 0s for the network bits and 1s for the host bits: /24 becomes 0.0.0.255. Subnet masks configure interfaces; wildcard masks are used in ACLs and OSPF network statements to match a range of addresses.

A /24 leaves 8 host bits, so it contains 2 to the power of 8, which is 256 addresses in total. Two of those are reserved: the first is the network address and the last is the broadcast address. That leaves 254 usable host addresses. The same rule generalises: usable hosts equal 2 to the power of the number of host bits, minus 2.

VLSM stands for Variable Length Subnet Masking: instead of giving every subnet the same size, you allocate each one the smallest block that fits its requirement. A point-to-point link needs only a /30, while a floor of 100 users needs a /25. This stops you wasting large blocks on tiny links, which matters because IPv4 address space is finite. The VLSM section above allocates largest-first, which is the ordering that keeps a plan tight.

Yes. The IPv6 section returns the network prefix, the expanded and compressed forms, the first and last address, the interface identifier, the total number of addresses in the block and the address type (global unicast, unique local or link-local). Note there is no broadcast address in IPv6, so every address in the prefix is usable, and prefixes longer than /64 break SLAAC autoconfiguration.