Subnet Calculator

Calculate subnet details for IPv4 and IPv6 networks. Enter an IP address with prefix length to get network information, host range, and subnet splitting.

How It Works

A subnet calculator determines network boundaries from an IP address and prefix length (CIDR notation). The prefix length specifies how many leading bits identify the network portion, while the remaining bits identify individual hosts.

IPv4 Subnetting

IPv4 addresses are 32 bits long, written as four octets in dotted-decimal notation (e.g. 192.168.1.0). A prefix of /24 means 24 bits for the network and 8 bits for hosts, giving 256 total addresses (254 usable, excluding network and broadcast addresses).

• Network address — all host bits set to 0
• Broadcast address — all host bits set to 1
• Subnet mask — prefix bits as 1s, host bits as 0s (e.g. 255.255.255.0 for /24)
• Wildcard mask — inverse of the subnet mask, used in ACLs

IPv6 Subnetting

IPv6 addresses are 128 bits long, written as eight groups of four hex digits separated by colons. The same prefix logic applies: a /64 network has 64 network bits and 64 host bits, yielding 2⁶⁴ addresses. IPv6 does not use broadcast addresses; multicast and anycast replace that function.

Subnet Splitting

Splitting divides a network into smaller, equal-sized subnets by borrowing additional bits from the host portion. For example, splitting a /24 into /25 subnets produces 2 subnets of 128 addresses each.