Visual lab
Learn subnetting visually
11 short lessons, from binary to IPv6. Change the inputs and watch every value update.
Test address
Used by lessons 2 to 4Tip: paste an address with a prefix, like 10.0.5.9/22
/25 · 255.255.255.128
Lesson 2 of 11Beginner
The 7 attributes
The 32-bit address/25
Network bits on the left of the prefix line, host bits on the right.
Network 25Host 7
Octet 110 / 255
Mask11111111
Octet 244 / 255
Mask11111111
Octet 321 / 255
Mask11111111
Octet 4Interesting148 / 128
Mask10000000
Hover or tap any bit to inspect it.
The 7 attributes
Every subnetting question asks for one of these. The block size is the shortcut to all of them.
1Subnet mask
255.255.255.128
Prefix /25
2Network address
10.44.21.128
All host bits 0
3First usable
10.44.21.129
Network + 1
4Last usable
10.44.21.254
Broadcast − 1
5Broadcast
10.44.21.255
All host bits 1
6Total addresses
128
2^7
7Usable hosts
126
2^7 − 2
Block size
128
256 − 128 in octet 4
Lock it in
Drill the “Network address” skill until it is automatic.
Lesson 2 of 11
Next: The 60-second method