Subnet-calculator

Subnet Calculator

Use this calculator to determine the network address, broadcast address, host range, and other important details for a given IP address and CIDR prefix.

function calculateSubnet() { var ipAddressStr = document.getElementById("ipAddress").value.trim(); var cidrPrefixStr = document.getElementById("cidrPrefix").value.trim(); var resultDiv = document.getElementById("subnetResult"); resultDiv.innerHTML = ""; // Clear previous results // — Input Validation — var ipParts = ipAddressStr.split('.'); if (ipParts.length !== 4) { resultDiv.innerHTML = "Error: Invalid IP Address format. Please use dotted decimal (e.g., 192.168.1.10)."; return; } var ipIntParts = []; for (var i = 0; i < 4; i++) { var part = parseInt(ipParts[i], 10); if (isNaN(part) || part 255) { resultDiv.innerHTML = "Error: Invalid IP Address octet. Each part must be between 0 and 255."; return; } ipIntParts.push(part); } var cidrPrefix = parseInt(cidrPrefixStr, 10); if (isNaN(cidrPrefix) || cidrPrefix 32) { resultDiv.innerHTML = "Error: Invalid CIDR Prefix. Must be a number between 0 and 32."; return; } // — IP Address to 32-bit integer — var ipAddressInt = (ipIntParts[0] << 24) | (ipIntParts[1] << 16) | (ipIntParts[2] << 8) | ipIntParts[3]; // — Subnet Mask (32-bit integer) from CIDR — var subnetMaskInt = -1 << (32 – cidrPrefix); // Creates a mask like 111…000 // — Network Address (32-bit integer) — var networkAddressInt = ipAddressInt & subnetMaskInt; // — Wildcard Mask (32-bit integer) — var wildcardMaskInt = ~subnetMaskInt; // Bitwise NOT // — Broadcast Address (32-bit integer) — var broadcastAddressInt = networkAddressInt | wildcardMaskInt; // — First Usable Host (32-bit integer) — var firstUsableHostInt = networkAddressInt + 1; // — Last Usable Host (32-bit integer) — var lastUsableHostInt = broadcastAddressInt – 1; // — Number of Usable Hosts — var numHosts = Math.pow(2, (32 – cidrPrefix)) – 2; if (cidrPrefix === 31) { // Special case for /31 (point-to-point) numHosts = 2; } else if (cidrPrefix === 32) { // Special case for /32 (single host) numHosts = 1; } else if (numHosts >> 24) & 0xFF) + '.' + ((ipInt >>> 16) & 0xFF) + '.' + ((ipInt >>> 8) & 0xFF) + '.' + (ipInt & 0xFF); } // — Convert all calculated integers back to dotted decimal — var networkAddress = intToIp(networkAddressInt); var broadcastAddress = intToIp(broadcastAddressInt); var firstUsableHost = (cidrPrefix === 31 || cidrPrefix === 32) ? "N/A" : intToIp(firstUsableHostInt); var lastUsableHost = (cidrPrefix === 31 || cidrPrefix === 32) ? "N/A" : intToIp(lastUsableHostInt); var subnetMaskDotted = intToIp(subnetMaskInt); var wildcardMaskDotted = intToIp(wildcardMaskInt); // — Display Results — var resultsHtml = "

Subnet Details:

"; resultsHtml += "IP Address: " + ipAddressStr + ""; resultsHtml += "CIDR Prefix: /" + cidrPrefix + ""; resultsHtml += "Subnet Mask: " + subnetMaskDotted + ""; resultsHtml += "Wildcard Mask: " + wildcardMaskDotted + ""; resultsHtml += "Network Address: " + networkAddress + ""; resultsHtml += "Broadcast Address: " + broadcastAddress + ""; resultsHtml += "First Usable Host: " + firstUsableHost + ""; resultsHtml += "Last Usable Host: " + lastUsableHost + ""; resultsHtml += "Total Hosts: " + Math.pow(2, (32 – cidrPrefix)) + ""; resultsHtml += "Usable Hosts: " + numHosts + ""; resultDiv.innerHTML = resultsHtml; } .subnet-calculator-container { font-family: Arial, sans-serif; max-width: 700px; margin: 20px auto; padding: 20px; border: 1px solid #ccc; border-radius: 8px; background-color: #f9f9f9; } .subnet-calculator-container h2 { text-align: center; color: #333; margin-bottom: 20px; } .subnet-calculator-container p { line-height: 1.6; margin-bottom: 10px; } .calculator-form label { display: inline-block; width: 150px; margin-bottom: 8px; font-weight: bold; } .calculator-form input[type="text"], .calculator-form input[type="number"] { width: calc(100% – 160px); padding: 8px; margin-bottom: 10px; border: 1px solid #ddd; border-radius: 4px; box-sizing: border-box; } .calculator-form button { display: block; width: 100%; padding: 10px 15px; background-color: #007bff; color: white; border: none; border-radius: 4px; font-size: 16px; cursor: pointer; transition: background-color 0.3s ease; } .calculator-form button:hover { background-color: #0056b3; } .calculator-result { margin-top: 20px; padding: 15px; border: 1px solid #e0e0e0; border-radius: 5px; background-color: #e9ecef; } .calculator-result h3 { color: #333; margin-top: 0; border-bottom: 1px solid #ccc; padding-bottom: 10px; margin-bottom: 15px; } .calculator-result p { margin-bottom: 8px; } .calculator-result p strong { display: inline-block; width: 180px; }

Understanding Subnetting

Subnetting is the process of dividing a large network into smaller, more efficient sub-networks (subnets). This practice is fundamental in network administration for several key reasons:

Why Subnet?

• Improved Network Performance: By reducing the size of broadcast domains, subnetting minimizes unnecessary network traffic, leading to faster communication within each subnet.
• Enhanced Security: Subnets can be isolated from each other, allowing administrators to apply different security policies to different segments of the network. This can prevent unauthorized access and contain security breaches.
• Efficient IP Address Utilization: Subnetting helps in conserving IP addresses, especially in IPv4, by allocating only the necessary number of addresses to each segment, rather than wasting large blocks.
• Easier Network Management: Smaller, more manageable subnets simplify troubleshooting, organization, and administration of network resources.

Key Subnetting Concepts:

IP Address:

A unique numerical label assigned to each device connected to a computer network that uses the Internet Protocol for communication. It consists of four octets (groups of 8 bits) 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 notation (e.g., 255.255.255.0) or CIDR notation.

CIDR Prefix (Classless Inter-Domain Routing):

A method for allocating IP addresses and routing IP packets. It's represented by a slash followed by a number (e.g., /24), indicating the number of bits in the IP address that represent the network portion.

Network Address:

The first address in a subnet. It identifies the subnet itself and cannot be assigned to a host. All devices within the same subnet share the same network address.

Broadcast Address:

The last address in a subnet. Packets sent to this address are delivered to all devices within that subnet. It also cannot be assigned to a host.

First Usable Host:

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:

The last IP address in a subnet that can be assigned to a device. It is always one less than the broadcast address.

Usable Hosts:

The total number of IP addresses available for assignment to devices within a subnet. This is calculated as 2(32 - CIDR Prefix) - 2 (subtracting the network and broadcast addresses). For /31 and /32 subnets, the rules for usable hosts differ slightly.

Wildcard Mask:

The inverse of the subnet mask. It's often used in access control lists (ACLs) on routers to specify a range of IP addresses. For example, if the subnet mask is 255.255.255.0, the wildcard mask is 0.0.0.255.

How the Calculator Works:

This calculator takes an IP address and a CIDR prefix as input. It then performs binary calculations to determine the network address, broadcast address, the range of usable host IP addresses, the subnet mask in dotted decimal, and the wildcard mask. It converts the IP address and subnet mask into their 32-bit binary representations to perform bitwise AND and OR operations, which are fundamental to subnetting.

Example:

Let's say you have an IP address 192.168.1.10 with a CIDR prefix of /24.

• IP Address: 192.168.1.10
• CIDR Prefix: /24
• Subnet Mask: 255.255.255.0
• Wildcard Mask: 0.0.0.255
• 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

This means that any device on this network will have an IP address between 192.168.1.1 and 192.168.1.254, and all will belong to the 192.168.1.0 network.