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Calculate an IPv4 subnet's network, broadcast, and usable host range.
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This tool calculates an IPv4 subnet's key details -- network address, broadcast address, first/last usable host, and total host count -- from an IP address and CIDR prefix length (like /24), essential for network planning and troubleshooting.
Enter an IP address and a CIDR prefix (0-32). The subnet's network address, broadcast address, and usable host range appear instantly.
The CIDR prefix defines a subnet mask (e.g. /24 = 255.255.255.0). The network address is the IP with all "host bits" zeroed; the broadcast address has all host bits set to 1. Usable hosts are everything between those two, excluding the network and broadcast addresses themselves -- except for /31 and /32, which have no usable range in the traditional sense.
192.168.1.100/24: network 192.168.1.0, broadcast 192.168.1.255, usable hosts 192.168.1.1 - 192.168.1.254 (254 total).
To generate random test IP addresses to practice on, see the Random IPv4 Generator.
Consider the hypothetical address 10.20.30.77 with prefix /26. A /26 leaves 6 host bits, so the block size is 64 addresses. The subnet boundaries in the last octet run 0, 64, 128, and 192. The address ends in 77, which sits between 64 and 127, so the network address is 10.20.30.64 and the broadcast address is 10.20.30.127. The first usable host is 10.20.30.65, the last is 10.20.30.126, and there are 62 usable addresses. The tool's Total Hosts tile will show 64, because it displays the full block size rather than the usable count. Remember to subtract two yourself for ordinary subnets when you need the number of assignable devices.
For a /31 the tool reports a total of 2, and it shows the network address as the first address and the broadcast address as the last, since there is no separate usable range in its calculation. In real point-to-point links under the /31 convention, both addresses can be used by the two ends. For /32 the total is 1 and the first and last address are the same single address. For /0 the block is the entire IPv4 space of about 4.29 billion addresses. Prefix values outside 0 to 32 are rejected with an error message, and so are addresses that do not have four dot-separated numbers between 0 and 255.
The tool covers IPv4 only. It does not know about your organisation's reserved addresses, so gateways, DHCP scopes, and static assignments are yours to plan on top of the usable range. Some cloud providers reserve extra addresses in each subnet, which reduces the usable count below what this tool shows, so check your provider's documentation before sizing a network to the last address. When you plan growth, leave spare room instead of choosing the smallest block that fits today.
It means the first 24 bits of the 32-bit IP address are the fixed network portion, leaving the remaining 8 bits for host addresses within that subnet -- a /24 always has 256 total addresses (254 usable).
The network address identifies the subnet itself, and the broadcast address is used to send a message to every device on the subnet at once -- neither can serve as an individual device's own address.
A /32 is a single host address with no subnet concept at all; a /31 (RFC 3021) is a special 2-address point-to-point link convention that skips the usual network/broadcast reservation, using both addresses as usable hosts.
The tile shows the whole block. Two addresses, the network and broadcast, are reserved in ordinary subnets, leaving 254 for devices.
No. Enter the prefix length as a number, for example 24 for 255.255.255.0 or 26 for 255.255.255.192.
The tool shows a message saying the entry is not a valid IPv4 address, or that the prefix must be between 0 and 32.
Reference: MDN Web Docs