1. What is CIDR Notation?

CIDR (Classless Inter-Domain Routing) notation is a compact representation of an IP address and its associated routing prefix. It's written as a suffix to the IP address like /24, where the number indicates the number of bits in the network portion of the address.

2. How Subnet Mask Calculation Works

The subnet mask is calculated from CIDR notation using:

Where:

• \( n \) — CIDR prefix length (0-32)
• The first \( n \) bits are set to 1
• The remaining \( 32-n \) bits are set to 0

Explanation: The subnet mask is a 32-bit number that separates the IP address into network and host portions. The network portion is represented by the 1's in the mask.

3. Importance of Subnet Masks

Details: Subnet masks are essential for defining network boundaries, routing traffic efficiently, and implementing network security policies. They help determine whether hosts are on the same network or need their traffic routed.

4. Using the Calculator

Tips: Enter the CIDR prefix length (0-32). The calculator will show both the dotted decimal notation (like 255.255.255.0) and binary representation of the subnet mask.

5. Frequently Asked Questions (FAQ)

Q1: What's the difference between /24 and 255.255.255.0?
A: They represent the same subnet mask - /24 is the CIDR notation, while 255.255.255.0 is the dotted decimal notation.

Q2: What does a /32 CIDR mean?
A: /32 means all 32 bits are network bits (subnet mask 255.255.255.255), representing a single host.

Q3: What's the smallest possible subnet?
A: The smallest is /31 (for point-to-point links) or /30 (with 2 usable hosts), though /32 is a single host.

Q4: Why are subnet masks important for routing?
A: Routers use subnet masks to determine whether to route packets to another network or keep them local.

Q5: How does CIDR relate to IPv4 address exhaustion?
A: CIDR allows for more efficient allocation of IP addresses by enabling variable-length subnet masking, reducing waste.