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Understanding Subnet Masks
A simple guide to how networks are divided, CIDR notation, and IP ranges.
Quick Answer
Why Do We Need Subnets?
Without subnets, every computer would be on one giant network, which would be chaotic and slow. Subnetting breaks networks into manageable pieces.
Think of an IP address like a street address:
- Network Portion: The specific street name.
- Host Portion: The house number.
The Subnet Mask is the line that tells you where the street name ends and the house number begins.
Common Subnet Masks
The most common subnet mask you will see in home networks is 255.255.255.0.
| Class | Subnet Mask | Addresses |
|---|---|---|
| Class A | 255.0.0.0 | 16 Million+ |
| Class B | 255.255.0.0 | 65,536 |
| Class C | 255.255.255.0 | 256 (254 usable) |
What is CIDR Notation? (/24)
CIDR (Classless Inter-Domain Routing) is a shorter way to write a subnet mask. Instead of writing 255.255.255.0, we write /24.
The number refers to how many bits are turned "on" (set to 1) in the mask.
/24= 24 bits on =11111111.11111111.11111111.00000000=255.255.255.0/16= 16 bits on =11111111.11111111.00000000.00000000=255.255.0.0/8= 8 bits on =11111111.00000000.00000000.00000000=255.0.0.0
Calculate Subnets Instantly
Avoid the math. Use our visual calculator to see IP ranges and CIDR blocks.
Open Subnet CalculatorCheatsheet: Usable IPs
- /32 = 1 IP (Specific Device)
- /30 = 4 IPs (2 Usable) - Point-to-Point links
- /29 = 8 IPs (6 Usable)
- /24 = 256 IPs (254 Usable) - Typical LAN
- /16 = 65,536 IPs - Large Enterprise