Enter an IP address and subnet mask to see the network details.
Network Details:
Network Address:
Broadcast Address:
Usable IP Range:
Total Hosts:
Usable Hosts:
CIDR Notation:
Understanding Subnetting
Subnetting is a fundamental networking technique that involves dividing a larger IP network into smaller, more manageable subnetworks. This process is crucial for efficient IP address allocation, improved network performance, enhanced security, and simplified administration.
Why Subnet?
Network Segmentation: Breaking down a large network into smaller ones helps to isolate traffic, reducing broadcast domain size and improving overall network efficiency.
Security: Subnets can be used to enforce security policies by controlling traffic flow between different network segments.
Performance: By reducing the size of broadcast domains, subnetting can decrease network congestion and improve data transmission speeds.
IP Address Management: It allows for more organized and efficient allocation of IP addresses, preventing waste and ensuring that addresses are available where needed.
How Subnetting Works (The Math)
Subnetting is achieved by borrowing bits from the host portion of an IP address to create subnet bits. This effectively extends the network portion of the address, creating distinct subnets.
Key Concepts:
IP Address: A unique identifier for a device on a network. IPv4 addresses are 32-bit numbers, typically represented in dotted-decimal notation (e.g., 192.168.1.0).
Subnet Mask: A 32-bit number that defines which part of an IP address is the network portion and which part is the host portion. In dotted-decimal notation, network bits are represented by '1's and host bits by '0's.
CIDR Notation: A compact way to represent an IP address and its subnet mask. It consists of the IP address followed by a slash and the number of network bits (e.g., 192.168.1.0/24).
Calculating Subnet Details:
Given an IP address and a subnet mask, we can determine the following:
Network Address: This is the first address in a subnet. It's calculated by performing a bitwise AND operation between the IP address and the subnet mask. All host bits in the network address are 0.
Broadcast Address: This is the last address in a subnet. It's calculated by taking the network address and setting all host bits to 1.
Usable IP Range: The range of IP addresses that can be assigned to devices within a subnet. It starts from the address immediately after the network address and ends at the address immediately before the broadcast address.
Total Hosts: The total number of IP addresses within a subnet, including the network and broadcast addresses. This is calculated as 2(number of host bits).
Usable Hosts: The number of IP addresses that can actually be assigned to devices. This is the total number of hosts minus 2 (for the network and broadcast addresses).
CIDR Notation: Derived from the subnet mask, it indicates the number of bits used for the network portion.
Example Calculation:
Let's take the IP address 192.168.1.75 and the subnet mask 255.255.255.0.
IP Address (Binary):11000000.10101000.00000001.01001011
Network Address: Performing bitwise AND: 11000000.10101000.00000001.00000000 which is 192.168.1.0.
Broadcast Address: Network Address with host bits set to 1: 11000000.10101000.00000001.11111111 which is 192.168.1.255.
Usable IP Range:192.168.1.1 to 192.168.1.254.
Total Hosts: 28 = 256.
Usable Hosts: 256 – 2 = 254.
CIDR Notation: /24.
function calculateSubnet() {
var ipAddress = document.getElementById("ipAddress").value;
var subnetMaskInput = document.getElementById("subnetMask").value;
var errorMessageDiv = document.getElementById("errorMessage");
var resultDiv = document.getElementById("result");
var resultDetailsDiv = document.getElementById("resultDetails");
errorMessageDiv.textContent = "";
resultDiv.innerHTML = "
Results
";
resultDetailsDiv.style.display = "none";
if (!ipAddress || !subnetMaskInput) {
errorMessageDiv.textContent = "Please enter both IP Address and Subnet Mask.";
return;
}
var ipParts = ipAddress.split('.');
if (ipParts.length !== 4 || ipParts.some(part => isNaN(parseInt(part)) || parseInt(part) 255)) {
errorMessageDiv.textContent = "Invalid IP Address format. Please use dotted-decimal notation (e.g., 192.168.1.0).";
return;
}
var subnetMask = [];
var cidr = 0;
if (subnetMaskInput.startsWith('/')) {
cidr = parseInt(subnetMaskInput.substring(1));
if (isNaN(cidr) || cidr 32) {
errorMessageDiv.textContent = "Invalid CIDR notation. Please use a value between /0 and /32.";
return;
}
for (var i = 0; i < 32; i++) {
if (i < cidr) {
subnetMask.push(255);
} else {
subnetMask.push(0);
}
}
// Convert back to dotted-decimal for consistency if needed, but we'll use binary logic
var tempMask = [];
for(var i = 0; i < 4; i++) {
var octet = 0;
for(var j = 0; j < 8; j++) {
if (i * 8 + j < cidr) {
octet |= (1 < isNaN(parseInt(part)) || parseInt(part) 255)) {
errorMessageDiv.textContent = "Invalid Subnet Mask format. Please use dotted-decimal notation (e.g., 255.255.255.0) or CIDR notation (e.g., /24).";
return;
}
subnetMask = maskParts.map(Number);
// Calculate CIDR from mask
var binaryMask = subnetMask.map(octet => octet.toString(2).padStart(8, '0')).join(");
cidr = binaryMask.split('0')[0].length;
}
// Validate subnet mask structure (must be contiguous 1s followed by 0s)
var binaryMaskString = subnetMask.map(octet => octet.toString(2).padStart(8, '0')).join(");
if (binaryMaskString.includes('01')) {
errorMessageDiv.textContent = "Invalid Subnet Mask. The bits must be contiguous (all 1s followed by all 0s).";
return;
}
var ipBinary = ipParts.map(octet => parseInt(octet).toString(2).padStart(8, '0')).join(");
var maskBinary = subnetMask.map(octet => octet.toString(2).padStart(8, '0')).join(");
var networkBinary = "";
for (var i = 0; i < 32; i++) {
networkBinary += (parseInt(ipBinary[i]) & parseInt(maskBinary[i])).toString();
}
var networkAddressParts = [];
for (var i = 0; i < 4; i++) {
networkAddressParts.push(parseInt(networkBinary.substring(i * 8, (i + 1) * 8), 2));
}
var networkAddress = networkAddressParts.join('.');
var hostBits = 32 – cidr;
var broadcastBinary = "";
for (var i = 0; i = cidr && i < 32)) {
broadcastBinary += '1';
} else {
broadcastBinary += '0';
}
}
var broadcastAddressParts = [];
for (var i = 0; i < 4; i++) {
broadcastAddressParts.push(parseInt(broadcastBinary.substring(i * 8, (i + 1) * 8), 2));
}
var broadcastAddress = broadcastAddressParts.join('.');
var totalHosts = Math.pow(2, hostBits);
var usableHosts = totalHosts – 2;
var usableIpStartBinary = networkBinary.substring(0, cidr) + '0'.repeat(hostBits);
usableIpStartBinary = usableIpStartBinary.substring(0, 31) + '1'; // Set last host bit to 1
var usableIpEndBinary = broadcastBinary.substring(0, 31) + '0'; // Set last host bit to 0
var usableIpStartParts = [];
for (var i = 0; i < 4; i++) {
usableIpStartParts.push(parseInt(usableIpStartBinary.substring(i * 8, (i + 1) * 8), 2));
}
var usableIpStart = usableIpStartParts.join('.');
var usableIpEndParts = [];
for (var i = 0; i = 0 ? usableHosts : 0; // Handle /31 and /32 cases
document.getElementById("cidrNotation").textContent = "/" + cidr;
resultDiv.innerHTML = "