The CIDR Range Calculator provides essential network details, including the Network Address, Broadcast Address, and the range of usable host IP addresses, based on a given IP and CIDR prefix.
CIDR Range Calculator
Network Address:
Broadcast Address:
Usable Host Range:
Total Hosts:
CIDR Range Calculation Logic:
The calculation is based on bitwise operations:
Mask Length (N) = CIDR Prefix
Host Bits (H) = 32 - N
Total Addresses = 2^H
Subnet Mask = (2^N - 1) left-shifted by H
Network Address = IP Address AND Subnet Mask
Broadcast Address = Network Address OR (2^H - 1)
Usable IP Range = (Network Address + 1) to (Broadcast Address - 1)
Source Reference: RFC 4632 – Classless Inter-Domain Routing, Cisco CIDR Primer
Variables (Inputs):
- IP Address: Any valid IPv4 address (four octets separated by dots) within the network segment you wish to analyze.
- CIDR Notation (/X): The Classless Inter-Domain Routing prefix, represented by a forward slash followed by a number between 0 and 32 (inclusive), indicating the length of the network portion of the address.
What is the CIDR Range Calculator?
The CIDR Range Calculator is an essential tool for network engineers and administrators. It simplifies the complex process of determining the boundaries of an IP subnet defined by a specific IP address and its associated CIDR prefix. Classless Inter-Domain Routing (CIDR) was introduced to replace the older classful networking system (A, B, C), allowing for more flexible and efficient allocation of IP addresses.
By taking the IP and the prefix length (e.g., /24), the calculator performs the necessary binary conversions and bitwise logic to output the network’s foundational addresses: the Network ID (the base address of the subnet), the Broadcast ID (used to send data to all hosts on the subnet), and the actual range of addresses available for client devices and servers.
How to Calculate a CIDR Range (Example)
Let’s calculate the range for the input 172.16.100.50/22:
- Determine Host Bits (H): The prefix is /22. Host bits $H = 32 – 22 = 10$.
- Calculate Subnet Mask: The mask has 22 ones, followed by 10 zeros. This translates to $255.255.252.0$ in dotted-decimal notation.
- Determine Network Address: Perform a bitwise AND operation between the IP address ($172.16.100.50$) and the Subnet Mask ($255.255.252.0$). The result is $172.16.100.0$. This is the Network Address.
- Determine Broadcast Address: The broadcast address is the address where all host bits are set to 1. In this case, it is $172.16.103.255$.
- Usable Host Range: The first usable IP is the Network Address plus one ($172.16.100.1$), and the last usable IP is the Broadcast Address minus one ($172.16.103.254$).
Frequently Asked Questions (FAQ)
- How many usable hosts are available in a /28 subnet? A /28 prefix leaves $32 – 28 = 4$ host bits. The total number of addresses is $2^4 = 16$. Since the network and broadcast addresses are reserved, the usable hosts are $16 – 2 = 14$.
- What is the difference between a Network Address and a Broadcast Address? The Network Address is the lowest address in the subnet and identifies the subnet itself. The Broadcast Address is the highest address and is used to communicate with all devices simultaneously on that subnet.
- What is supernetting? Supernetting is the opposite of subnetting. It combines multiple smaller networks (subnets) into a larger single network, typically done by shortening the CIDR prefix (e.g., changing from /24 to /20).
- Can I use a /31 or /32 prefix? A /31 (2 total addresses) is often used for point-to-point links (RFC 3021). A /32 (1 total address) is a host route and has no range, only one specific address. The calculator typically focuses on subnets allowing for multiple hosts.