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/

With subnet mask practice: https://richtechguy.com/subnetting-practice-tool/

CIDR Calculator: https://cidr.xyz/

Networking Classes

How Many Possible

All of the possible hosts, not just usable (eg, not subtracting network and broadcast).

• 4th octet: 256 (255.255.255.0)
• 3rd octet: 65,536 (255.255.0.0)
• 2nd octet: 16,777,216 (255.255.0.0)
• 1st octet: 4,294,967,296 (0.0.0.0), all of them

If you want to see how many are in a 255.240.0.0, you'd multiple the number leftover in the 2nd octet (256-240 = 16) x 65536, because each of those 16 could be a network as big as 65536.

For 255.255.240.0, that would be 16 x 255.

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.