Ip Address to Subnet Mask Calculator

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IP Address to Subnet Mask Calculator

Subnet Details:

Subnet Mask:

Network Address:

Broadcast Address:

Usable Host IP Range:

Total Hosts:

Usable Hosts:

function calculateSubnet() { var ipAddressStr = document.getElementById("ipAddress").value; var cidrPrefix = parseInt(document.getElementById("cidrPrefix").value, 10); // — Input Validation — var ipParts = ipAddressStr.split('.'); if (ipParts.length !== 4) { alert("Invalid IP Address format. Please use dotted decimal notation (e.g., 192.168.1.1)."); return; } var ipOctets = []; for (var i = 0; i < 4; i++) { var octet = parseInt(ipParts[i], 10); if (isNaN(octet) || octet 255) { alert("Invalid IP Address octet: " + ipParts[i] + ". Octets must be between 0 and 255."); return; } ipOctets.push(octet); } if (isNaN(cidrPrefix) || cidrPrefix 32) { alert("Invalid CIDR Prefix. Please enter a number between 0 and 32."); return; } // — Subnet Mask Calculation — var subnetMaskOctets = []; for (var i = 0; i < 4; i++) { var octetValue = 0; for (var j = 0; j 0) { octetValue = (octetValue << 1) | 1; cidrPrefix–; } else { octetValue = (octetValue << 1) | 0; } } subnetMaskOctets.push(octetValue); } var subnetMask = subnetMaskOctets.join('.'); // — Network Address Calculation — var networkAddressOctets = []; for (var i = 0; i < 4; i++) { networkAddressOctets.push(ipOctets[i] & subnetMaskOctets[i]); } var networkAddress = networkAddressOctets.join('.'); // — Broadcast Address Calculation — var broadcastAddressOctets = []; var invertedSubnetMaskOctets = []; for (var i = 0; i 2) ? (totalHosts – 2) : 0; if (usableHosts > 0) { var firstUsableOctets = networkAddressOctets.slice(); firstUsableOctets[3]++; // Increment last octet for first usable IP firstUsableIp = firstUsableOctets.join('.'); var lastUsableOctets = broadcastAddressOctets.slice(); lastUsableOctets[3]–; // Decrement last octet for last usable IP lastUsableIp = lastUsableOctets.join('.'); } else if (numHostBits === 1) { // For /31, 2 hosts, no usable range firstUsableIp = "N/A (Point-to-point link)"; lastUsableIp = "N/A (Point-to-point link)"; } else if (numHostBits === 0) { // For /32, 1 host, no usable range firstUsableIp = "N/A (Single host address)"; lastUsableIp = "N/A (Single host address)"; } // — Display Results — document.getElementById("resultSubnetMask").innerHTML = "Subnet Mask: " + subnetMask; document.getElementById("resultNetworkAddress").innerHTML = "Network Address: " + networkAddress; document.getElementById("resultBroadcastAddress").innerHTML = "Broadcast Address: " + broadcastAddress; document.getElementById("resultUsableHostRange").innerHTML = "Usable Host IP Range: " + firstUsableIp + " – " + lastUsableIp; document.getElementById("resultTotalHosts").innerHTML = "Total Hosts: " + totalHosts; document.getElementById("resultUsableHosts").innerHTML = "Usable Hosts: " + usableHosts; } // Calculate on page load with default values window.onload = calculateSubnet;

Understanding IP Addresses and Subnet Masks

In the world of computer networking, IP addresses and subnet masks are fundamental concepts that allow devices to communicate with each other. This calculator helps you quickly determine key subnetting details from an IP address and its CIDR prefix.

What is an IP Address?

An Internet Protocol (IP) address is a unique numerical label assigned to each device connected to a computer network that uses the Internet Protocol for communication. For IPv4 (the most common version), an IP address is a 32-bit number typically expressed in dotted-decimal notation, like 192.168.1.10. It consists of four sets of numbers (octets), each ranging from 0 to 255, separated by dots.

An IP address serves two main functions: host or network interface identification and location addressing. It tells devices both who they are and where they are on a network.

The Role of a Subnet Mask

While an IP address identifies a device, a subnet mask helps a device determine which part of an IP address refers to the network and which part refers to the specific host (device) within that network. It's a 32-bit number that "masks" the IP address, dividing it into two parts:

  • Network Portion: Identifies the specific network the device belongs to. All devices on the same local 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.

Like an IP address, a subnet mask is also expressed in dotted-decimal notation (e.g., 255.255.255.0). Where there's a '1' in the binary representation of the subnet mask, that bit in the IP address belongs to the network portion. Where there's a '0', it belongs to the host portion.

CIDR (Classless Inter-Domain Routing)

CIDR is a method for allocating IP addresses and routing IP packets. It was introduced to replace the older classful networking system, which was inefficient in IP address allocation. CIDR uses a "prefix length" (often written as /N, where N is a number from 0 to 32) to indicate how many bits of the IP address are used for the network portion.

For example, /24 means the first 24 bits of the IP address are for the network, and the remaining 8 bits are for hosts. This directly translates to a subnet mask of 255.255.255.0 (24 ones followed by 8 zeros in binary).

Key Subnetting Concepts Explained

  • Subnet Mask: The 32-bit mask that separates the network and host portions of an IP address.
  • Network Address: The first address in a subnet. It's obtained by performing a bitwise AND operation between the IP address and the subnet mask. The host portion of this address is all zeros. This address is reserved and cannot be assigned to a host.
  • Broadcast Address: The last address in a subnet. It's obtained by setting all host bits to '1'. This address is used to send data to all devices on that specific subnet and is also reserved.
  • Usable Host IP Range: The range of IP addresses between the network address and the broadcast address (exclusive). These are the addresses that can actually be assigned to devices like computers, servers, and printers.
  • Total Hosts: The total number of IP addresses available within a given subnet, calculated as 2^(32 - CIDR Prefix).
  • Usable Hosts: The number of IP addresses that can be assigned to devices. This is typically Total Hosts - 2, accounting for the reserved network and broadcast addresses. For very small subnets (like /31 or /32), the number of usable hosts can be 0.

How to Use This Calculator

Simply enter an IP address (e.g., 192.168.1.100) and its corresponding CIDR prefix (e.g., 24 for a /24 network). The calculator will instantly provide you with the subnet mask, network address, broadcast address, the range of usable host IPs, and the total and usable number of hosts for that subnet.

Example Usage:

Let's say you have an IP address 172.16.10.50 with a CIDR prefix of 20.

  • IP Address: 172.16.10.50
  • CIDR Prefix: 20

The calculator would output:

  • Subnet Mask: 255.255.240.0
  • Network Address: 172.16.0.0
  • Broadcast Address: 172.16.15.255
  • Usable Host IP Range: 172.16.0.1 - 172.16.15.254
  • Total Hosts: 4096
  • Usable Hosts: 4094

This tool is invaluable for network administrators, IT professionals, and anyone learning about networking fundamentals, helping to demystify the process of subnetting.

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