CIDR Netmask Calculator
Calculation Results:
Network Address:
Broadcast Address:
Netmask:
Wildcard Mask:
Total Hosts:
Usable Hosts:
First Usable Host:
Last Usable Host:
Error: Invalid IP Address format.
Please enter a valid IPv4 address (e.g., 192.168.1.0).'; return; } var cidrPrefix = parseInt(cidrPrefixInput, 10); if (isNaN(cidrPrefix) || cidrPrefix 32) { resultDiv.innerHTML = 'Error: Invalid CIDR Prefix.
Please enter a number between 0 and 32.'; return; } var ipInt = dottedDecimalToInt(ipAddressInput); // Calculate Netmask var netmaskInt = (0xFFFFFFFF <>> 0; var netmaskDotted = intToDottedDecimal(netmaskInt); // Calculate Network Address var networkAddressInt = (ipInt & netmaskInt) >>> 0; var networkAddressDotted = intToDottedDecimal(networkAddressInt); // Calculate Broadcast Address var wildcardMaskInt = (~netmaskInt) >>> 0; var broadcastAddressInt = (networkAddressInt | wildcardMaskInt) >>> 0; var broadcastAddressDotted = intToDottedDecimal(broadcastAddressInt); var wildcardMaskDotted = intToDottedDecimal(wildcardMaskInt); // Calculate Number of Hosts var totalHosts = Math.pow(2, (32 – cidrPrefix)); var usableHosts = 0; if (cidrPrefix 0) { var firstUsableHostInt = (networkAddressInt + 1) >>> 0; firstUsableHostDotted = intToDottedDecimal(firstUsableHostInt); var lastUsableHostInt = (broadcastAddressInt – 1) >>> 0; lastUsableHostDotted = intToDottedDecimal(lastUsableHostInt); } else if (cidrPrefix === 32) { firstUsableHostDotted = ipAddressInput; // For /32, the IP itself is the only host lastUsableHostDotted = ipAddressInput; } // Display results resultDiv.innerHTML = 'Calculation Results:
'; networkAddressSpan.textContent = networkAddressDotted; broadcastAddressSpan.textContent = broadcastAddressDotted; netmaskSpan.textContent = netmaskDotted; wildcardMaskSpan.textContent = wildcardMaskDotted; totalHostsSpan.textContent = totalHosts.toLocaleString(); usableHostsSpan.textContent = usableHosts.toLocaleString(); firstUsableHostSpan.textContent = firstUsableHostDotted; lastUsableHostSpan.textContent = lastUsableHostDotted; } // Run calculation on page load with default values window.onload = calculateCIDR;Understanding CIDR and Netmasks
The CIDR Netmask Calculator is an essential tool for network administrators, IT professionals, and anyone working with IP addressing. It helps in understanding how IP addresses are divided into network and host portions, enabling efficient network design and troubleshooting.
What is CIDR?
CIDR stands for Classless Inter-Domain Routing. Introduced in 1993, CIDR revolutionized IP addressing by replacing the rigid class-based system (Class A, B, C) with a more flexible and efficient method. Before CIDR, IP addresses were allocated in large, fixed blocks, leading to rapid depletion of available IP addresses and inefficient use of the address space.
With CIDR, IP addresses are assigned using a variable-length subnet mask, denoted by a slash followed by a number (e.g., /24). This number, known as the CIDR prefix or subnet mask length, indicates how many bits in the IP address are used for the network portion, with the remaining bits used for the host portion.
What is a Netmask?
A Netmask (or Subnet Mask) is a 32-bit number that separates the network address from the host address within an IP address. In binary, the netmask consists of a series of '1's followed by a series of '0's. The '1's correspond to the network portion of the IP address, and the '0's correspond to the host portion.
For example, a CIDR prefix of /24 means the first 24 bits are for the network, and the remaining 8 bits (32 – 24) are for hosts. The corresponding netmask in dotted decimal format would be 255.255.255.0.
Key Components of CIDR Calculation:
- IP Address: The starting point for the calculation, typically a network address or an address within a subnet.
- CIDR Prefix: The number of bits used for the network portion of the IP address (0-32).
- Network Address: The first address in a subnet. All devices on the same subnet share the same network address. It's identified by setting all host bits to '0'.
- Broadcast Address: The last address in a subnet. Packets sent to this address are delivered to all devices on that subnet. It's identified by setting all host bits to '1'.
- Netmask: The 32-bit mask that defines the network and host portions.
- Wildcard Mask: The inverse of the netmask. It's often used in access control lists (ACLs) to specify a range of IP addresses.
- Total Hosts: The total number of IP addresses available within the subnet, including the network and broadcast addresses. Calculated as 2^(32 – CIDR Prefix).
- Usable Hosts: The number of IP addresses available for assigning to devices within the subnet. This is typically Total Hosts – 2 (excluding the network and broadcast addresses). For /31 and /32 subnets, the usable hosts are 0.
- First Usable Host: The first IP address that can be assigned to a device in the subnet (Network Address + 1).
- Last Usable Host: The last IP address that can be assigned to a device in the subnet (Broadcast Address – 1).
How the Calculator Works:
Our CIDR Netmask Calculator takes an IP address and a CIDR prefix as input. It then performs binary arithmetic to determine all the critical network parameters:
- It converts the IP address into its 32-bit binary representation.
- Based on the CIDR prefix, it generates the corresponding netmask in binary and then converts it to dotted decimal format.
- It performs a bitwise AND operation between the IP address and the netmask to find the Network Address.
- It calculates the Wildcard Mask by inverting the netmask.
- It performs a bitwise OR operation between the Network Address and the Wildcard Mask to find the Broadcast Address.
- Finally, it calculates the total and usable host counts, and derives the first and last usable host addresses.
Example Usage:
Let's say you have an IP address 192.168.10.50 with a CIDR prefix of /26.
- Input IP Address: 192.168.10.50
- Input CIDR Prefix: 26
The calculator would yield results similar to these:
- Network Address: 192.168.10.0
- Broadcast Address: 192.168.10.63
- Netmask: 255.255.255.192
- Wildcard Mask: 0.0.0.63
- Total Hosts: 64
- Usable Hosts: 62
- First Usable Host: 192.168.10.1
- Last Usable Host: 192.168.10.62
This means that for the 192.168.10.0/26 network, you have 62 IP addresses (from 192.168.10.1 to 192.168.10.62) that can be assigned to devices.