Network Subnet Calculator
Subnet Details:
| Network Address: |
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| Broadcast Address: |
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| First Usable Host: |
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| Last Usable Host: |
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| Subnet Mask (Decimal): |
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| Subnet Mask (Binary): |
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| CIDR Prefix: |
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| Total Hosts: |
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| Usable Hosts: |
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| IP Class: |
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.subnet-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: #f9f9f9;
box-shadow: 0 4px 12px rgba(0, 0, 0, 0.08);
}
.subnet-calculator-container h2 {
text-align: center;
color: #333;
margin-bottom: 25px;
font-size: 28px;
border-bottom: 2px solid #007bff;
padding-bottom: 10px;
}
.calculator-form .form-group {
margin-bottom: 18px;
}
.calculator-form label {
display: block;
margin-bottom: 8px;
font-weight: bold;
color: #555;
font-size: 16px;
}
.calculator-form input[type="text"] {
width: calc(100% – 22px);
padding: 12px;
border: 1px solid #ccc;
border-radius: 6px;
font-size: 16px;
box-sizing: border-box;
transition: border-color 0.3s ease;
}
.calculator-form input[type="text"]:focus {
border-color: #007bff;
outline: none;
box-shadow: 0 0 5px rgba(0, 123, 255, 0.3);
}
.calculator-form button {
display: block;
width: 100%;
padding: 12px 20px;
background-color: #007bff;
color: white;
border: none;
border-radius: 6px;
font-size: 18px;
font-weight: bold;
cursor: pointer;
transition: background-color 0.3s ease, transform 0.2s ease;
margin-top: 20px;
}
.calculator-form button:hover {
background-color: #0056b3;
transform: translateY(-2px);
}
.calculator-form button:active {
transform: translateY(0);
}
.calculator-results {
margin-top: 30px;
padding-top: 20px;
border-top: 1px solid #eee;
}
.calculator-results h3 {
color: #333;
font-size: 22px;
margin-bottom: 15px;
text-align: center;
}
.calculator-results table {
width: 100%;
border-collapse: collapse;
margin-top: 15px;
}
.calculator-results table td {
padding: 10px 0;
border-bottom: 1px dashed #e9e9e9;
font-size: 15px;
color: #444;
}
.calculator-results table tr:last-child td {
border-bottom: none;
}
.calculator-results table td:first-child {
width: 50%;
font-weight: bold;
color: #333;
}
.calculator-results table td:last-child {
text-align: right;
color: #007bff;
font-weight: 600;
}
#errorMessage {
text-align: center;
font-weight: bold;
margin-top: 15px;
}
.subnet-article {
font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
max-width: 700px;
margin: 40px auto;
padding: 25px;
background-color: #ffffff;
border: 1px solid #e0e0e0;
border-radius: 10px;
box-shadow: 0 4px 12px rgba(0, 0, 0, 0.08);
line-height: 1.6;
color: #333;
}
.subnet-article h2 {
color: #007bff;
font-size: 28px;
margin-bottom: 20px;
text-align: center;
}
.subnet-article h3 {
color: #0056b3;
font-size: 22px;
margin-top: 25px;
margin-bottom: 15px;
border-bottom: 1px solid #eee;
padding-bottom: 5px;
}
.subnet-article p {
margin-bottom: 15px;
font-size: 16px;
}
.subnet-article ul {
list-style-type: disc;
margin-left: 25px;
margin-bottom: 15px;
}
.subnet-article ul li {
margin-bottom: 8px;
font-size: 16px;
}
.subnet-article strong {
color: #000;
}
function isValidOctet(octetStr) {
var num = parseInt(octetStr, 10);
return !isNaN(num) && num >= 0 && num <= 255 && String(num) === octetStr;
}
function parseAndValidateIP(ipStr) {
var parts = ipStr.split('.');
if (parts.length !== 4) {
return null;
}
var octets = [];
for (var i = 0; i >> 0).toString(2);
// Pad with leading zeros to 32 bits
binaryMask = "00000000000000000000000000000000".substr(binaryMask.length) + binaryMask;
var foundZero = false;
for (var i = 0; i < binaryMask.length; i++) {
if (binaryMask[i] === '1') {
if (foundZero) {
return false; // Found a '1' after a '0'
}
} else { // binaryMask[i] === '0'
foundZero = true;
}
}
return true;
}
function parseAndValidateSubnetMask(maskStr) {
var parts = maskStr.split('.');
if (parts.length !== 4) {
return null;
}
var octets = [];
var maskInt = 0;
for (var i = 0; i < 4; i++) {
if (!isValidOctet(parts[i])) {
return null;
}
var octetVal = parseInt(parts[i], 10);
octets.push(octetVal);
maskInt = (maskInt <>> 24) & 0xFF;
var oct2 = (intVal >>> 16) & 0xFF;
var oct3 = (intVal >>> 8) & 0xFF;
var oct4 = intVal & 0xFF;
return oct1 + '.' + oct2 + '.' + oct3 + '.' + oct4;
}
function intToBinaryDottedDecimal(intVal) {
var oct1 = ((intVal >>> 24) & 0xFF).toString(2).padStart(8, '0');
var oct2 = ((intVal >>> 16) & 0xFF).toString(2).padStart(8, '0');
var oct3 = ((intVal >>> 8) & 0xFF).toString(2).padStart(8, '0');
var oct4 = (intVal & 0xFF).toString(2).padStart(8, '0');
return oct1 + '.' + oct2 + '.' + oct3 + '.' + oct4;
}
function calculateSubnet() {
var ipAddressInput = document.getElementById("ipAddress").value.trim();
var subnetMaskInput = document.getElementById("subnetMask").value.trim();
var errorMessageDiv = document.getElementById("errorMessage");
errorMessageDiv.innerHTML = ""; // Clear previous errors
var ipOctets = parseAndValidateIP(ipAddressInput);
if (!ipOctets) {
errorMessageDiv.innerHTML = "Invalid IP Address format. Please use A.B.C.D (e.g., 192.168.1.10).";
return;
}
var maskOctets = parseAndValidateSubnetMask(subnetMaskInput);
if (!maskOctets) {
errorMessageDiv.innerHTML = "Invalid Subnet Mask format or structure. Please use A.B.C.D (e.g., 255.255.255.0) with contiguous 1s followed by 0s.";
return;
}
var ipInt = (ipOctets[0] << 24) | (ipOctets[1] << 16) | (ipOctets[2] << 8) | ipOctets[3];
var maskInt = (maskOctets[0] << 24) | (maskOctets[1] << 16) | (maskOctets[2] <= 0; i–) {
if (((maskInt >>> i) & 1) === 1) {
cidrPrefix++;
} else {
break;
}
}
var networkInt = ipInt & maskInt;
var broadcastInt = networkInt | (~maskInt & 0xFFFFFFFF); // Use & 0xFFFFFFFF to ensure 32-bit unsigned result
var totalHosts = Math.pow(2, (32 – cidrPrefix));
var usableHosts = 0;
if (cidrPrefix 0) {
firstUsableHost = intToDottedDecimal(networkInt + 1);
lastUsableHost = intToDottedDecimal(broadcastInt – 1);
} else if (cidrPrefix === 32) {
firstUsableHost = "N/A (Single Host)";
lastUsableHost = "N/A (Single Host)";
} else { // /31 or /32 (if usableHosts is 0)
firstUsableHost = "N/A (No Usable Hosts)";
lastUsableHost = "N/A (No Usable Hosts)";
}
var firstOctet = ipOctets[0];
var ipClass = "";
if (firstOctet >= 1 && firstOctet = 128 && firstOctet = 192 && firstOctet = 224 && firstOctet = 240 && firstOctet <= 255) {
ipClass = "E (Experimental)";
} else {
ipClass = "Reserved/Special";
}
document.getElementById("networkAddress").innerHTML = intToDottedDecimal(networkInt);
document.getElementById("broadcastAddress").innerHTML = intToDottedDecimal(broadcastInt);
document.getElementById("firstUsableHost").innerHTML = firstUsableHost;
document.getElementById("lastUsableHost").innerHTML = lastUsableHost;
document.getElementById("subnetMaskDecimal").innerHTML = subnetMaskInput;
document.getElementById("subnetMaskBinary").innerHTML = intToBinaryDottedDecimal(maskInt);
document.getElementById("cidrPrefix").innerHTML = "/" + cidrPrefix;
document.getElementById("totalHosts").innerHTML = totalHosts;
document.getElementById("usableHosts").innerHTML = usableHosts;
document.getElementById("ipClass").innerHTML = ipClass;
}
// Initial calculation on page load for default values
document.addEventListener('DOMContentLoaded', function() {
calculateSubnet();
});
Understanding Network Subnetting
Network subnetting is a fundamental concept in computer networking that involves dividing a larger network into smaller, more manageable subnetworks (subnets). This process is crucial for efficient IP address management, improved network performance, and enhanced security.
Why Subnet? The Benefits
- Improved Network Performance: By segmenting a large network, broadcast traffic is confined to smaller subnets, reducing congestion and improving overall network speed.
- Enhanced Security: Subnetting allows network administrators to isolate different departments or types of traffic, preventing unauthorized access between segments and containing security breaches.
- Efficient IP Address Utilization: In the past, classful IP addressing often led to wasted IP addresses. Subnetting, especially with CIDR, allows for more flexible and efficient allocation of IP addresses, conserving the limited IPv4 address space.
- Easier Network Management: Smaller subnets are easier to manage, troubleshoot, and scale. It simplifies routing tables and network organization.
Key Subnetting Concepts
To effectively use a subnet calculator and understand its output, it's important to grasp these core terms:
- IP Address (IPv4): A unique numerical label assigned to each device connected to a computer network that uses the Internet Protocol for communication. It consists of four numbers (octets) separated by dots, e.g.,
192.168.1.10.
- Subnet Mask: A 32-bit number that distinguishes the network portion of an IP address from the host portion. It's represented in dotted-decimal format (e.g.,
255.255.255.0) or CIDR notation. The '1's in the binary subnet mask represent the network portion, and the '0's represent the host portion.
- CIDR Prefix (Classless Inter-Domain Routing): A more flexible way to denote the subnet mask, represented as a slash followed by a number (e.g.,
/24). This number indicates the count of contiguous '1's in the subnet mask, signifying the length of the network portion of the IP address.
- Network Address: The first address in a subnet. It's used to identify the entire network segment and cannot be assigned to a host device. It's derived by performing a bitwise AND operation between the IP address and the subnet mask.
- Broadcast Address: The last address in a subnet. Packets sent to this address are delivered to all devices within that specific subnet. It also cannot be assigned to a host device.
- First Usable Host IP: The first IP address in a subnet that can be assigned to a device. It is always one greater than the Network Address.
- Last Usable Host IP: The last IP address in a subnet that can be assigned to a device. It is always one less than the Broadcast Address.
- Total Hosts: The total number of IP addresses available within a given subnet, including the network and broadcast addresses. Calculated as
2^(32 - CIDR Prefix).
- Usable Hosts: The number of IP addresses within a subnet that can actually be assigned to devices. This is typically
Total Hosts - 2 (subtracting the network and broadcast addresses). For very small subnets (like /31 or /32), this can be 0 or 1.
- IP Class: Historically, IP addresses were categorized into classes (A, B, C, D, E) based on their first octet. While CIDR has largely replaced classful addressing, understanding IP classes can still provide context for network size and common usage.
How the Calculator Works
This calculator takes an IP Address and a Subnet Mask as input. It then performs the necessary binary calculations to determine all the critical subnet details:
- It validates the input IP address and subnet mask for correct format and structure.
- It converts both the IP address and subnet mask into their 32-bit binary representations.
- It calculates the CIDR prefix by counting the leading '1's in the subnet mask.
- Using bitwise operations (AND, OR), it determines the Network Address and Broadcast Address.
- From these, it derives the First Usable Host IP, Last Usable Host IP, Total Hosts, and Usable Hosts.
- Finally, it identifies the IP Class based on the first octet of the provided IP address.
Examples of Subnetting
Example 1: Standard Class C Network
Let's say you have an IP Address 192.168.1.10 and a standard Subnet Mask 255.255.255.0.
- IP Address: 192.168.1.10
- Subnet Mask: 255.255.255.0
- CIDR Prefix: /24
- Network Address: 192.168.1.0
- Broadcast Address: 192.168.1.255
- First Usable Host: 192.168.1.1
- Last Usable Host: 192.168.1.254
- Total Hosts: 256
- Usable Hosts: 254
- IP Class: C
This is a common setup for small home or office networks, providing 254 usable IP addresses.
Example 2: Subnetting a Class C Network into Smaller Segments
Imagine you need to divide the 192.168.1.0/24 network into smaller subnets, each capable of supporting about 30 hosts. A /27 subnet mask (255.255.255.224) would be suitable.
If your IP Address is 192.168.1.45 and Subnet Mask is 255.255.255.224:
- IP Address: 192.168.1.45
- Subnet Mask: 255.255.255.224
- CIDR Prefix: /27
- Network Address: 192.168.1.32
- Broadcast Address: 192.168.1.63
- First Usable Host: 192.168.1.33
- Last Usable Host: 192.168.1.62
- Total Hosts: 32
- Usable Hosts: 30
- IP Class: C
In this scenario, the original /24 network is divided into 8 subnets (2^(27-24) = 2^3 = 8), each with 30 usable hosts. The IP 192.168.1.45 falls into the subnet ranging from 192.168.1.32 to 192.168.1.63.
Example 3: A Class B Network
Consider a larger network with an IP Address 172.16.50.100 and a Subnet Mask 255.255.0.0.
- IP Address: 172.16.50.100
- Subnet Mask: 255.255.0.0
- CIDR Prefix: /16
- Network Address: 172.16.0.0
- Broadcast Address: 172.16.255.255
- First Usable Host: 172.16.0.1
- Last Usable Host: 172.16.255.254
- Total Hosts: 65,536
- Usable Hosts: 65,534
- IP Class: B
This represents a very large network segment, common in medium to large organizations.
Conclusion
Subnetting is an indispensable skill for network professionals. It allows for the creation of robust, efficient, and secure network infrastructures. This subnet calculator simplifies the complex binary math involved, providing quick and accurate results for network planning and troubleshooting.