.subnetting-calculator-container {
font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
max-width: 700px;
margin: 20px auto;
padding: 25px;
border: 1px solid #e0e0e0;
border-radius: 10px;
background-color: #fdfdfd;
box-shadow: 0 4px 12px rgba(0, 0, 0, 0.05);
}
.subnetting-calculator-container h2 {
text-align: center;
color: #333;
margin-bottom: 25px;
font-size: 1.8em;
}
.subnetting-calculator-container .input-group {
margin-bottom: 18px;
display: flex;
flex-direction: column;
}
.subnetting-calculator-container label {
display: block;
margin-bottom: 8px;
color: #555;
font-weight: bold;
font-size: 0.95em;
}
.subnetting-calculator-container input[type="text"],
.subnetting-calculator-container input[type="number"] {
width: calc(100% – 20px);
padding: 12px;
border: 1px solid #ccc;
border-radius: 6px;
font-size: 1em;
box-sizing: border-box;
transition: border-color 0.3s ease;
}
.subnetting-calculator-container input[type="text"]:focus,
.subnetting-calculator-container input[type="number"]:focus {
border-color: #007bff;
outline: none;
box-shadow: 0 0 0 3px rgba(0, 123, 255, 0.25);
}
.subnetting-calculator-container button {
display: block;
width: 100%;
padding: 14px;
background-color: #007bff;
color: white;
border: none;
border-radius: 6px;
font-size: 1.1em;
font-weight: bold;
cursor: pointer;
transition: background-color 0.3s ease, transform 0.2s ease;
margin-top: 20px;
}
.subnetting-calculator-container button:hover {
background-color: #0056b3;
transform: translateY(-2px);
}
.subnetting-calculator-container .results {
margin-top: 30px;
padding-top: 25px;
border-top: 1px solid #eee;
}
.subnetting-calculator-container .results h3 {
color: #333;
margin-bottom: 20px;
text-align: center;
font-size: 1.5em;
}
.subnetting-calculator-container .result-item {
display: flex;
justify-content: space-between;
padding: 10px 0;
border-bottom: 1px dashed #eee;
}
.subnetting-calculator-container .result-item:last-child {
border-bottom: none;
}
.subnetting-calculator-container .result-item strong {
color: #333;
font-weight: 600;
}
.subnetting-calculator-container .result-item span {
color: #007bff;
font-weight: 500;
}
.subnetting-calculator-container .error-message {
color: #dc3545;
margin-top: 15px;
text-align: center;
font-weight: bold;
}
@media (max-width: 600px) {
.subnetting-calculator-container {
padding: 15px;
}
.subnetting-calculator-container h2 {
font-size: 1.5em;
}
.subnetting-calculator-container button {
font-size: 1em;
padding: 12px;
}
}
function calculateSubnet() {
var ipAddressInput = document.getElementById("ipAddress").value;
var cidrPrefixInput = parseInt(document.getElementById("cidrPrefix").value, 10);
var errorMessageDiv = document.getElementById("errorMessage");
errorMessageDiv.textContent = ""; // Clear previous errors
// Validate IP Address format
var ipParts = ipAddressInput.split('.');
if (ipParts.length !== 4 || ipParts.some(function(part) {
var num = parseInt(part, 10);
return isNaN(num) || num 255;
})) {
errorMessageDiv.textContent = "Invalid IP Address format. Please use dotted decimal (e.g., 192.168.1.1).";
clearResults();
return;
}
// Validate CIDR Prefix
if (isNaN(cidrPrefixInput) || cidrPrefixInput 32) {
errorMessageDiv.textContent = "Invalid CIDR Prefix. Please enter a number between 0 and 32.";
clearResults();
return;
}
// Convert IP to 32-bit integer
var ipInt = (parseInt(ipParts[0], 10) << 24) |
(parseInt(ipParts[1], 10) << 16) |
(parseInt(ipParts[2], 10) < 0) {
subnetMaskInt = 0xFFFFFFFF <>> 24) & 0xFF) + '.' +
((intVal >>> 16) & 0xFF) + '.' +
((intVal >>> 8) & 0xFF) + '.' +
(intVal & 0xFF);
}
var networkAddress = intToIp(networkAddressInt);
var broadcastAddress = intToIp(broadcastAddressInt);
var subnetMask = intToIp(subnetMaskInt);
// Calculate First and Last Usable Hosts
var firstUsableHost = "N/A";
var lastUsableHost = "N/A";
var totalHosts = Math.pow(2, (32 – cidrPrefixInput));
var usableHosts = 0;
if (cidrPrefixInput < 31) { // For /31 and /32, there are no usable hosts
firstUsableHost = intToIp(networkAddressInt + 1);
lastUsableHost = intToIp(broadcastAddressInt – 1);
usableHosts = totalHosts – 2;
} else if (cidrPrefixInput === 31) { // /31 has 2 total hosts, 0 usable
firstUsableHost = "N/A (Point-to-point link)";
lastUsableHost = "N/A (Point-to-point link)";
usableHosts = 0;
} else if (cidrPrefixInput === 32) { // /32 has 1 total host, 0 usable
firstUsableHost = "N/A (Single host address)";
lastUsableHost = "N/A (Single host address)";
usableHosts = 0;
}
// Convert subnet mask to binary
var binarySubnetMask = "";
for (var i = 0; i >> (31 – i)) & 1);
if ((i + 1) % 8 === 0 && i < 31) {
binarySubnetMask += ".";
}
}
// Display results
document.getElementById("networkAddress").textContent = networkAddress;
document.getElementById("broadcastAddress").textContent = broadcastAddress;
document.getElementById("subnetMask").textContent = subnetMask;
document.getElementById("binarySubnetMask").textContent = binarySubnetMask;
document.getElementById("firstUsableHost").textContent = firstUsableHost;
document.getElementById("lastUsableHost").textContent = lastUsableHost;
document.getElementById("totalHosts").textContent = totalHosts;
document.getElementById("usableHosts").textContent = usableHosts;
}
function clearResults() {
document.getElementById("networkAddress").textContent = "";
document.getElementById("broadcastAddress").textContent = "";
document.getElementById("subnetMask").textContent = "";
document.getElementById("binarySubnetMask").textContent = "";
document.getElementById("firstUsableHost").textContent = "";
document.getElementById("lastUsableHost").textContent = "";
document.getElementById("totalHosts").textContent = "";
document.getElementById("usableHosts").textContent = "";
}
// Initial calculation on page load for default values
window.onload = calculateSubnet;
IP Subnetting Calculator
Subnet Details
Network Address:
Broadcast Address:
Subnet Mask (Dotted Decimal):
Subnet Mask (Binary):
First Usable Host:
Last Usable Host:
Total Hosts:
Usable Hosts:
Understanding IP Subnetting: A Comprehensive Guide
IP subnetting is a fundamental concept in computer networking that allows network administrators to divide a large network into smaller, more manageable subnetworks. This process enhances network efficiency, improves security, and optimizes IP address allocation. Our IP Subnetting Calculator helps you quickly determine critical network parameters based on an IP address and its CIDR prefix.
What is Subnetting?
At its core, subnetting involves taking a single IP network and breaking it down into multiple smaller networks, known as subnets. Each subnet operates as an independent network, even though they all share the same initial IP address range. This is achieved by "borrowing" bits from the host portion of an IP address and using them for the network portion, effectively extending the network address and reducing the number of available host addresses within that segment.
Why is Subnetting Important?
- Improved Network Performance: By reducing the size of broadcast domains, subnetting minimizes unnecessary network traffic. Broadcasts are contained within their respective subnets, preventing them from flooding the entire network and slowing down devices.
- Enhanced Security: Subnetting allows for the isolation of different departments or types of traffic. For example, a guest Wi-Fi network can be placed on a separate subnet from a corporate network, preventing unauthorized access to sensitive resources.
- Efficient IP Address Management: Subnetting helps conserve IP addresses, especially in IPv4 where addresses are a finite resource. Instead of allocating a large block of addresses to a small department, you can create a subnet that perfectly fits its needs, leaving more addresses available for other uses.
- Simplified Troubleshooting: When network issues arise, isolating the problem to a specific subnet makes troubleshooting faster and more efficient.
- Organizational Structure: Subnetting can mirror an organization's physical or logical structure, making network design and management more intuitive.
How Subnetting Works: The Role of the Subnet Mask and CIDR
An IP address (IPv4) is a 32-bit number, typically represented in dotted-decimal notation (e.g., 192.168.1.1). It consists of two main parts: the network portion and the host portion.
- Network Portion: Identifies the specific network to which the device belongs. All devices on the same network share the same network portion.
- Host Portion: Identifies the specific device within that network. Each device on a network must have a unique host portion.
The division between the network and host portions is determined by the subnet mask. A subnet mask is also a 32-bit number, represented in dotted-decimal (e.g., 255.255.255.0) or binary. In binary, the subnet mask consists of a series of '1's followed by a series of '0's. The '1's indicate the network portion, and the '0's indicate the host portion.
Classless Inter-Domain Routing (CIDR) notation provides a more concise way to represent the subnet mask. Instead of writing out the full dotted-decimal mask, CIDR uses a slash followed by a number (e.g., /24). This number indicates the count of '1's in the subnet mask, which directly corresponds to the length of the network portion of the IP address.
- A /24 CIDR prefix means there are 24 bits for the network portion and 8 bits (32-24) for the host portion. The subnet mask would be 255.255.255.0.
- A /27 CIDR prefix means 27 bits for the network and 5 bits (32-27) for the host. The subnet mask would be 255.255.255.224.
Key Subnetting Terms Explained
Our calculator provides several important outputs. Here's what they mean:
- Network Address: This is the first address in a subnet. It's used to identify the subnet itself and cannot be assigned to a host. In binary, all host bits are set to '0'.
- Broadcast Address: This is the last address in a subnet. It's used to send data to all devices within that specific subnet simultaneously and cannot be assigned to a host. In binary, all host bits are set to '1'.
- Subnet Mask (Dotted Decimal & Binary): As explained above, this defines the network and host portions of an IP address.
- First Usable Host: This is the first IP address in the subnet that can be assigned to a device (e.g., a computer, server, or router interface). It's always one greater than the Network Address.
- Last Usable Host: This is the last IP address in the subnet that can be assigned to a device. It's always one less than the Broadcast Address.
- Total Hosts: The total number of IP addresses available within the subnet, including the network and broadcast addresses. This is calculated as 2(32 – CIDR Prefix).
- Usable Hosts: The number of IP addresses that can actually be assigned to devices. This is typically Total Hosts – 2 (subtracting the network and broadcast addresses). For /31 and /32 subnets, there are no usable hosts.
Example: Subnetting 192.168.10.50/27
Let's use the calculator with an example: IP Address: 192.168.10.50 and CIDR Prefix: 27.
Here's what the calculator would determine:
- Subnet Mask: 255.255.255.224 (Binary: 11111111.11111111.11111111.11100000)
- Network Address: 192.168.10.32
- Broadcast Address: 192.168.10.63
- First Usable Host: 192.168.10.33
- Last Usable Host: 192.168.10.62
- Total Hosts: 32 (2(32-27) = 25 = 32)
- Usable Hosts: 30 (32 – 2)
This means that for the IP address 192.168.10.50 with a /27 prefix, the device is part of a subnet that starts at 192.168.10.32 and ends at 192.168.10.63, with 30 available IP addresses for devices.
Using an IP subnetting calculator simplifies what can be a complex manual calculation process, making network planning and management much easier for IT professionals and students alike.