Enter an IP address and subnet mask to see results.
Understanding IP Addresses and Subnet Masks
In computer networking, an IP address is a unique numerical label assigned to each device connected to a computer network that uses the Internet Protocol for communication. It serves two main functions: host or network interface identification and location addressing.
A subnet mask is used in conjunction with an IP address to divide it into a network address and a host address. It's a 32-bit number that masks an IP address, specifying which part of the IP address represents the network and which part represents the host. The subnet mask works by having a contiguous block of '1's followed by a contiguous block of '0's. The '1's indicate the network portion, and the '0's indicate the host portion.
How the Calculation Works
The calculation of network information from an IP address and subnet mask involves bitwise operations.
Network Address: This is calculated by performing a bitwise AND operation between the IP address and the subnet mask. This operation effectively isolates the network portion of the IP address.
Broadcast Address: This is calculated by taking the network address, inverting the host portion bits (changing the '0's to '1's), and then combining it with the network portion. It's used to send data to all devices on a specific subnet.
Number of Hosts: The number of usable IP addresses for devices on the subnet is determined by the number of host bits. If there are 'n' host bits (the number of '0's in the subnet mask), then the total number of possible host addresses is 2n. However, the network address and the broadcast address are reserved, so the number of usable hosts is 2n – 2.
CIDR Notation: CIDR (Classless Inter-Domain Routing) notation is a compact way to represent the subnet mask. It consists of the IP address followed by a forward slash and the number of bits in the subnet mask (which corresponds to the number of '1's in the subnet mask). For example, 192.168.1.0/24 means an IP address of 192.168.1.0 with a subnet mask that has 24 bits set to '1' (255.255.255.0).
Example Calculation
Let's consider an IP Address: 192.168.1.100 and Subnet Mask: 255.255.255.0
Binary Representation:
IP Address: 11000000.10000000.00000001.01100100
Subnet Mask: 11111111.11111111.11111111.00000000
Network Address (IP AND Mask):
11000000.10000000.00000001.00000000 = 192.168.1.0
Broadcast Address: The host portion (last 8 bits) of the network address (192.168.1.0) is all zeros. To get the broadcast address, we set all host bits to ones.
Network part: 192.168.1.
Host part (all ones): 11111111 = 255
Broadcast Address: 192.168.1.255
Number of Hosts: The subnet mask 255.255.255.0 has 24 bits for the network and 8 bits for the host (0 in the last octet).
Number of host bits (n) = 8
Total addresses = 28 = 256
Usable hosts = 28 – 2 = 256 – 2 = 254
CIDR Notation: Since there are 24 bits set to '1' in the subnet mask, the CIDR notation is /24. The full representation is 192.168.1.0/24.
Use Cases
This calculator is essential for network administrators, IT professionals, and anyone involved in setting up or managing computer networks. It helps in:
Planning network IP addressing schemes.
Troubleshooting network connectivity issues.
Determining the correct subnet masks for different network segments.
Understanding IP address ranges and broadcast addresses within a subnet.
Ensuring efficient allocation of IP addresses and avoiding conflicts.
function isValidIPv4(ip) {
if (typeof ip !== 'string') return false;
var parts = ip.split('.');
if (parts.length !== 4) return false;
for (var i = 0; i < parts.length; i++) {
var part = parseInt(parts[i], 10);
if (isNaN(part) || part 255) {
return false;
}
// Check for leading zeros in octets (e.g., 192.168.01.1) which are invalid in some contexts.
if (parts[i].length > 1 && parts[i].startsWith('0')) {
return false;
}
}
return true;
}
function isValidSubnetMask(mask) {
if (typeof mask !== 'string') return false;
if (mask === "0.0.0.0" || mask === "255.255.255.255") return true; // Edge cases
var parts = mask.split('.');
if (parts.length !== 4) return false;
var foundZeroOctet = false;
for (var i = 0; i < parts.length; i++) {
var part = parseInt(parts[i], 10);
if (isNaN(part) || part 255) {
return false;
}
if (part !== 255 && part !== 0) {
// Check if the non-255/0 octet is a valid subnet part (e.g., 254, 252, 248, etc.)
var binaryPart = part.toString(2).padStart(8, '0');
if (binaryPart.includes('01')) { // Invalid if a 0 is followed by a 1
return false;
}
}
if (part === 0) {
foundZeroOctet = true;
} else if (part !== 255 && foundZeroOctet) {
// If we've already seen a 0 octet, the next octet must be 0 for a valid mask
return false;
}
// Check for leading zeros in octets (e.g., 255.255.01.0)
if (parts[i].length > 1 && parts[i].startsWith('0')) {
return false;
}
}
return true;
}
function ipToBinary(ip) {
var parts = ip.split('.');
var binary = "";
for (var i = 0; i < parts.length; i++) {
binary += parseInt(parts[i], 10).toString(2).padStart(8, '0');
}
return binary;
}
function binaryToIp(binary) {
var ip = "";
for (var i = 0; i < binary.length; i += 8) {
var octet = parseInt(binary.substring(i, i + 8), 2);
ip += octet + ".";
}
return ip.slice(0, -1);
}
function calculateSubnetInfo() {
var ipAddress = document.getElementById("ipAddress").value;
var subnetMask = document.getElementById("subnetMask").value;
var resultDiv = document.getElementById("result");
if (!isValidIPv4(ipAddress) || !isValidSubnetMask(subnetMask)) {
resultDiv.innerHTML = "Invalid IP Address or Subnet Mask format. Please enter valid IPv4 addresses.";
return;
}
var ipBinary = ipToBinary(ipAddress);
var maskBinary = ipToBinary(subnetMask);
var networkBinary = "";
var broadcastBinary = "";
var cidr = 0;
for (var i = 0; i < 32; i++) {
// Network Address
if (maskBinary[i] === '1' && ipBinary[i] === '1') {
networkBinary += '1';
} else {
networkBinary += '0';
}
// Count CIDR
if (maskBinary[i] === '1') {
cidr++;
}
}
// Broadcast Address: Invert host bits of network address
var networkAddress = binaryToIp(networkBinary);
var hostBitsStart = cidr;
broadcastBinary = networkBinary.substring(0, hostBitsStart); // Network portion
for (var i = hostBitsStart; i < 32; i++) {
broadcastBinary += '1'; // Set host bits to 1
}
var broadcastAddress = binaryToIp(broadcastBinary);
var numberOfHostBits = 32 – cidr;
var totalAddresses = Math.pow(2, numberOfHostBits);
var usableHosts = totalAddresses – 2;
// Ensure usableHosts is not negative if mask is 255.255.255.255 (0 hosts) or 0.0.0.0 (invalid context for hosts)
if (subnetMask === "255.255.255.255") {
usableHosts = 0;
} else if (subnetMask === "0.0.0.0") {
usableHosts = "N/A (Invalid Mask for Host Allocation)";
} else if (usableHosts < 0) { // Should not happen with valid masks but as a safeguard
usableHosts = 0;
}
resultDiv.innerHTML =
'Network Address: ' + networkAddress + " +
'Broadcast Address: ' + broadcastAddress + " +
'CIDR Notation: /' + cidr + " +
'Total Addresses: ' + totalAddresses + " +
'Usable Host Addresses: ' + usableHosts + ";
}