A network mask, also known as a subnet mask, is a 32-bit number that separates the IP address into two parts: the network address and the host address. It's crucial for routing data packets efficiently within a network. Every device on a TCP/IP network requires a unique IP address and a subnet mask to communicate.
What is an IP Address?
An Internet Protocol (IP) address is a numerical label assigned to each device connected to a computer network that uses the Internet Protocol for communication. IPv4 addresses are 32-bit numbers, typically represented in dotted-decimal notation (e.g., 192.168.1.1). They are fundamental for identifying devices and their location on a network.
The Role of the Subnet Mask
The subnet mask works in conjunction with the IP address to determine which part of the IP address identifies the network and which part identifies the specific host within that network. When a device needs to send data, it uses the subnet mask to determine if the destination IP address is on the same local network or a different network. If it's on a different network, the data is sent to a router.
Network Address: The portion of the IP address that identifies the specific network segment. All devices on the same network segment share the same network address.
Host Address: The portion of the IP address that identifies a specific device within that network segment. Each device must have a unique host address within its network.
CIDR Notation
Classless Inter-Domain Routing (CIDR) is a method for allocating IP addresses and for IP routing. It was introduced to slow the growth of routing tables on routers across the Internet and to help slow the rapid exhaustion of IPv4 addresses. CIDR notation appends a slash and a number (e.g., /24) to the IP address, indicating the number of bits in the network portion of the address. For example, 192.168.1.0/24 means that the first 24 bits identify the network, and the remaining 8 bits identify the hosts.
Why Use a Network Mask Calculator?
Manually calculating network addresses, broadcast addresses, and usable host ranges can be complex and error-prone, especially for larger networks or when dealing with custom subnet masks. A network mask calculator simplifies this process by instantly providing all the necessary details based on an IP address and a subnet mask (either in dotted-decimal or CIDR format). This tool is invaluable for network administrators, IT professionals, and anyone learning about networking concepts.
Key Outputs Explained:
Network Address: The first address in the subnet, used to identify the network itself.
Broadcast Address: The last address in the subnet, used to send data to all devices on that network segment simultaneously.
First Usable Host: The first IP address that can be assigned to a device within the subnet (Network Address + 1).
Last Usable Host: The last IP address that can be assigned to a device within the subnet (Broadcast Address – 1).
Total Hosts: The total number of IP addresses available within the subnet, including the network and broadcast addresses.
Usable Hosts: The number of IP addresses that can actually be assigned to devices (Total Hosts – 2).
Subnet Mask (Dotted Decimal): The subnet mask represented in the familiar 255.255.255.0 format.
Subnet Mask (CIDR): The subnet mask represented in CIDR notation (e.g., /24).
Wildcard Mask: The inverse of the subnet mask, often used in Access Control Lists (ACLs) on routers to specify a range of IP addresses.
Network Mask Calculator
Enter an IP address and a subnet mask (either in dotted decimal or CIDR notation) to calculate network details.
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// Helper function to convert dotted decimal IP/mask to 32-bit integer
function ipToDec(ip) {
var parts = ip.split('.');
if (parts.length !== 4) return NaN;
var dec = 0;
for (var i = 0; i < 4; i++) {
var part = parseInt(parts[i], 10);
if (isNaN(part) || part 255) return NaN;
dec = (dec <>> 0; // Ensure unsigned 32-bit
}
// Helper function to convert 32-bit integer to dotted decimal IP/mask
function decToIp(dec) {
return ((dec >>> 24) & 0xFF) + '.' +
((dec >>> 16) & 0xFF) + '.' +
((dec >>> 8) & 0xFF) + '.' +
(dec & 0xFF);
}
// Helper function to convert CIDR to dotted decimal mask
function cidrToMask(cidr) {
var numBits = parseInt(cidr.substring(1), 10);
if (isNaN(numBits) || numBits 32) return null;
var maskDec = 0xFFFFFFFF <>> 0); // Ensure unsigned 32-bit
}
// Helper function to convert dotted decimal mask to CIDR
function maskToCidr(mask) {
var maskDec = ipToDec(mask);
if (isNaN(maskDec)) return null;
var count = 0;
for (var i = 0; i >> (31 – i)) & 1) {
count++;
} else {
// If a 0 is encountered, all subsequent bits must be 0 for a valid mask
for (var j = i; j >> (31 – j)) & 1) !== 0) {
return null; // Invalid mask (e.g., 255.255.254.1)
}
}
break;
}
}
return '/' + count;
}
// Helper function to validate IP address format
function isValidIp(ip) {
return /^(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)$/.test(ip);
}
// Helper function to validate dotted decimal mask format (contiguous 1s followed by 0s)
function isValidDottedMask(mask) {
var maskDec = ipToDec(mask);
if (isNaN(maskDec)) return false;
// Check if it's a valid contiguous mask (e.g., 255.255.255.0 is valid, 255.255.0.255 is not)
var invertedMask = (~maskDec) & 0xFFFFFFFF;
return ((invertedMask + 1) & invertedMask) === 0;
}
// Main calculation function
function calculateNetworkDetails() {
var ipAddressInput = document.getElementById('ipAddress').value.trim();
var subnetMaskInput = document.getElementById('subnetMask').value.trim();
var resultDiv = document.getElementById('result');
resultDiv.innerHTML = "; // Clear previous results
var ipDec;
if (!isValidIp(ipAddressInput)) {
resultDiv.innerHTML = 'Error: Invalid IP Address format. Please enter a valid IPv4 address (e.g., 192.168.1.100).';
return;
}
ipDec = ipToDec(ipAddressInput);
var maskDec;
var dottedMask;
var cidrNotation;
if (subnetMaskInput.startsWith('/')) {
// CIDR notation
var cidrValue = parseInt(subnetMaskInput.substring(1), 10);
if (isNaN(cidrValue) || cidrValue 32) {
resultDiv.innerHTML = 'Error: Invalid CIDR value. Must be between /0 and /32.';
return;
}
dottedMask = cidrToMask(subnetMaskInput);
maskDec = ipToDec(dottedMask);
cidrNotation = subnetMaskInput;
} else {
// Dotted decimal mask
if (!isValidDottedMask(subnetMaskInput)) {
resultDiv.innerHTML = 'Error: Invalid Subnet Mask format or non-contiguous mask. Please use a valid dotted decimal mask (e.g., 255.255.255.0).';
return;
}
dottedMask = subnetMaskInput;
maskDec = ipToDec(dottedMask);
cidrNotation = maskToCidr(dottedMask);
if (cidrNotation === null) { // Should not happen if isValidDottedMask passed, but as a safeguard
resultDiv.innerHTML = 'Error: Could not convert dotted decimal mask to CIDR. Mask might be invalid.';
return;
}
}
// Calculate Network Address
var networkDec = ipDec & maskDec;
var networkAddress = decToIp(networkDec);
// Calculate Broadcast Address
var broadcastDec = networkDec | (~maskDec & 0xFFFFFFFF);
var broadcastAddress = decToIp(broadcastDec);
// Calculate Total Hosts
var totalHosts = (broadcastDec – networkDec) + 1;
// Calculate Usable Hosts
var usableHosts = (totalHosts > 2) ? (totalHosts – 2) : 0;
// Calculate First Usable Host
var firstUsableHost = (usableHosts > 0) ? decToIp(networkDec + 1) : 'N/A (No usable hosts)';
// Calculate Last Usable Host
var lastUsableHost = (usableHosts > 0) ? decToIp(broadcastDec – 1) : 'N/A (No usable hosts)';
// Calculate Wildcard Mask
var wildcardMaskDec = (~maskDec) & 0xFFFFFFFF;
var wildcardMask = decToIp(wildcardMaskDec);
// Display results
var outputHtml = '