Subnet Calculator

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What is Subnetting?

Imagine the internet is like a postal system. Your IP address is your house address, and subnetting is like dividing a city into neighborhoods.

Subnetting breaks a large network into smaller, more manageable pieces called subnets. Each subnet is like a neighborhood where devices can talk to each other directly.

Why does this matter?

• Security: Keep sensitive devices (like servers) separate from guest WiFi
• Performance: Reduce network congestion by limiting broadcast traffic
• Organization: Group related devices together logically

Understanding CIDR Notation

You've probably seen IP addresses written like 192.168.1.0/24. That /24 at the end is CIDR notation (Classless Inter-Domain Routing).

The number after the slash tells you how many bits of the IP address identify the network portion:

Network vs Host Portions

Every IP address has two parts:

1. Network portion: Identifies which network you're on (like a street name)
2. Host portion: Identifies your specific device (like a house number)

For 192.168.1.100/24:

• Network: 192.168.1.0 (first 24 bits)
• Host: .100 (last 8 bits)
• All devices from 192.168.1.1 to 192.168.1.254 are on the same network

Special Addresses in Every Subnet

Every subnet reserves two addresses that you cannot assign to devices:

🔒 Network Address (first address)

• Example: 192.168.1.0 in a /24 network
• Identifies the network itself
• Used in routing tables

📢 Broadcast Address (last address)

• Example: 192.168.1.255 in a /24 network
• Messages sent here reach ALL devices on the subnet
• Used for network discovery protocols

That's why a /24 network has 256 total addresses but only 254 usable hosts!

Private vs Public IP Addresses

Not all IP addresses can be used on the public internet:

🏠 Private Ranges (use freely in your network):

• 10.0.0.0/8 — 16 million addresses
• 172.16.0.0/12 — 1 million addresses
• 192.168.0.0/16 — 65,000 addresses

🌐 Public Addresses: Assigned by your ISP, visible on the internet

Practical Subnetting Tips

1. Plan for Growth If you need 50 hosts now, use /25 (126 hosts) not /26 (62 hosts). Networks always grow!

2. Use Standard Boundaries Stick to /24, /25, /26, /27, /28 - they're easier to troubleshoot and remember.

3. Document Everything Keep a spreadsheet of your subnets. Future you will thank present you.

4. Leave Room Between Subnets If possible, don't use consecutive subnet ranges. This gives flexibility to expand later.

5. Consider VLANs Combine subnetting with VLANs for even better network segmentation.