Subnetting

September 12, 2025 note-to-self full-stack

Subnetting Cheat Sheet**:

128 64  32  16  8   4   2   1
128 192 224 240 248 252 254 255
/25 /26 /27 /28 /29 /30 /31 /32
/17 /18 /19 /20 /21 /22 /23 /24
/9  /10 /11 /12 /13 /14 /15 /16
/1  /2  /3  /4  /5  /6  /7  /8

Using that cheatsheet, solve for:

Network ID:
First Usable IP:
Last Usable IP:
Broadcast ID:
Next Network:
Subnet Mask:
Number of Hosts:

Subnetting practice: https://subnetipv4.com/

CIDR Calculator: https://cidr.xyz/

Useful Linux app:

ipcalc --split 2 $(curl -s ha17.com/ip)

Might need:

sudo apt update && sudo apt install ipcalc

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Private Network Ranges

  • 10.0.0.0 to 10.255.255.255 (Class A): This range offers over 16 million IP addresses and is typically used for large networks, like large corporations.
  • 172.16.0.0 to 172.31.255.255 (Class B): This range provides more than one million IP addresses and is suitable for medium-sized networks, such as schools or medium-sized businesses.
  • 192.168.0.0 to 192.168.255.255 (Class C): This range provides over 65,000 IP addresses and is commonly used for home and small office networks.

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** I needed this a lot at first but suddenly find it pretty easy to do this from memory.

These posts are for my own understanding. Reader beware. Info may be wrong but it reflects my current understanding.