Use this calculator to determine the network address, broadcast address, first and last host addresses, and the total number of usable hosts for a given IPv4 address and subnet mask.
Understanding IPv4 Subnetting
IPv4 (Internet Protocol version 4) addresses are 32-bit numbers that uniquely identify devices on a network. They are typically represented in dotted-decimal notation, such as 192.168.1.1, where each of the four numbers (octets) ranges from 0 to 255.
What is a Subnet Mask?
A subnet mask is used to divide an IP address into two parts: the network portion and the host portion. This division allows for the creation of smaller, more manageable networks called subnets. Subnet masks can be expressed in two ways:
Dotted-Decimal Notation: For example, 255.255.255.0. This mask indicates that the first three octets (24 bits) represent the network, and the last octet (8 bits) represents the hosts.
CIDR (Classless Inter-Domain Routing) Notation: For example, /24. This is a shorthand that indicates the number of bits in the network portion of the address. A /24 mask means 24 bits are for the network, leaving 8 bits for hosts.
Key IP Address Components
When you subnet a network, several important addresses are derived:
Network Address: This is the first address in a subnet. It identifies the network itself and cannot be assigned to a host. All host bits are set to 0. For example, for 192.168.1.1/24, the network address is 192.168.1.0.
Broadcast Address: This is the last address in a subnet. It is used to send data to all devices within that specific subnet and cannot be assigned to a host. All host bits are set to 1. For example, for 192.168.1.1/24, the broadcast address is 192.168.1.255.
First Host Address: This is the first usable IP address that can be assigned to a device within the subnet. It is always one greater than the network address. For 192.168.1.0/24, the first host is 192.168.1.1.
Last Host Address: This is the last usable IP address that can be assigned to a device within the subnet. It is always one less than the broadcast address. For 192.168.1.0/24, the last host is 192.168.1.254.
Total Usable Hosts: This is the number of IP addresses available for assignment to devices within the subnet. It is calculated as 2^(number of host bits) - 2 (subtracting the network and broadcast addresses). For a /24 network (8 host bits), this is 2^8 - 2 = 256 - 2 = 254 usable hosts.
How the Calculator Works
This calculator takes an IP address and a subnet mask (either in dotted-decimal or CIDR format) and performs bitwise operations to determine all the critical network parameters. It converts the IP address and subnet mask into their binary representations, applies the mask to identify the network and host portions, and then calculates the various addresses and host counts.
Example Usage:
Let's say you have an IP address 172.16.10.50 and a subnet mask of 255.255.252.0 (which is /22 CIDR).
IP Address:172.16.10.50
Subnet Mask:255.255.252.0 (or /22)
The calculator would output:
Network Address:172.16.8.0
Broadcast Address:172.16.11.255
First Host Address:172.16.8.1
Last Host Address:172.16.11.254
Total Usable Hosts:1022
Subnet Mask (Dotted Decimal):255.255.252.0
Subnet Mask (CIDR Prefix):/22
This information is crucial for network administrators to plan and manage IP address allocation efficiently, ensuring proper network segmentation and communication.
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function ipToLong(ip) {
var parts = ip.split('.');
if (parts.length !== 4) return NaN;
var longIp = 0;
for (var i = 0; i < 4; i++) {
var octet = parseInt(parts[i], 10);
if (isNaN(octet) || octet 255) return NaN;
longIp = (longIp <>> 0; // Ensure unsigned 32-bit
}
function longToIp(longIp) {
return ((longIp >>> 24) & 0xFF) + '.' +
((longIp >>> 16) & 0xFF) + '.' +
((longIp >>> 8) & 0xFF) + '.' +
(longIp & 0xFF);
}
function cidrToMaskLong(cidr) {
if (cidr 32) return NaN;
return (0xFFFFFFFF <>> 0;
}
function maskLongToCidr(maskLong) {
if (maskLong === 0) return 0; // Special case for /0
var cidr = 0;
var tempMask = maskLong;
while ((tempMask & 0x80000000) !== 0 && cidr < 32) {
cidr++;
tempMask = (tempMask <>> 0;
}
// Validate if the mask is contiguous (all ones followed by all zeros)
if (tempMask !== 0) return NaN; // Not a valid contiguous mask
return cidr;
}
function calculateIPDetails() {
var ipAddressStr = document.getElementById("ipAddress").value.trim();
var subnetMaskStr = document.getElementById("subnetMask").value.trim();
var resultDiv = document.getElementById("result");
resultDiv.innerHTML = ""; // Clear previous results
var ipLong = ipToLong(ipAddressStr);
if (isNaN(ipLong)) {
resultDiv.innerHTML = "Error: Invalid IP Address format. Please use dotted decimal (e.g., 192.168.1.1).";
return;
}
var maskLong;
var cidrPrefix;
var dottedDecimalMask;
if (subnetMaskStr.startsWith('/')) {
cidrPrefix = parseInt(subnetMaskStr.substring(1), 10);
if (isNaN(cidrPrefix) || cidrPrefix 32) {
resultDiv.innerHTML = "Error: Invalid CIDR prefix. Must be between /0 and /32.";
return;
}
maskLong = cidrToMaskLong(cidrPrefix);
dottedDecimalMask = longToIp(maskLong);
} else {
maskLong = ipToLong(subnetMaskStr);
if (isNaN(maskLong)) {
resultDiv.innerHTML = "Error: Invalid Subnet Mask format. Please use dotted decimal (e.g., 255.255.255.0) or CIDR (e.g., /24).";
return;
}
cidrPrefix = maskLongToCidr(maskLong);
if (isNaN(cidrPrefix)) {
resultDiv.innerHTML = "Error: Invalid Subnet Mask. Dotted decimal mask must be contiguous (e.g., 255.255.255.0, not 255.255.255.1).";
return;
}
dottedDecimalMask = subnetMaskStr;
}
var networkAddressLong = (ipLong & maskLong) >>> 0;
var broadcastAddressLong = (networkAddressLong | (~maskLong)) >>> 0;
var networkAddress = longToIp(networkAddressLong);
var broadcastAddress = longToIp(broadcastAddressLong);
var firstHostAddress = "N/A";
var lastHostAddress = "N/A";
var totalHosts = 0;
var numHostBits = 32 – cidrPrefix;
if (numHostBits >= 2) { // At least 2 host bits for usable hosts (network + broadcast)
firstHostAddress = longToIp(networkAddressLong + 1);
lastHostAddress = longToIp(broadcastAddressLong – 1);
totalHosts = Math.pow(2, numHostBits) – 2;
} else if (numHostBits === 1) { // /31 – Point-to-point links, 2 addresses, 0 usable hosts
firstHostAddress = "N/A (No usable hosts)";
lastHostAddress = "N/A (No usable hosts)";
totalHosts = 0;
} else if (numHostBits === 0) { // /32 – Single host address, 0 usable hosts
firstHostAddress = "N/A (Single host address)";
lastHostAddress = "N/A (Single host address)";
totalHosts = 0;
}
var output = "