What is the last usable host in 192.168.75.23/26?
How to use it
- Pick a difficulty: Easy keeps to /24–/30, Medium goes up to /16, Hard covers /8–/30.
- Type your answer and press Check. Wrong answers show the correct one and the full working; Show answer reveals it anytime.
- Press Next question for another, or start a timed quiz of ten questions to track your score and time.
What the result means
Each solution uses the block-size method, the fastest way to subnet in your head:
- Find the “interesting” octet: the one where the mask isn't 255 or 0.
- Block size = 256 − the mask value in that octet. For /20 (255.255.240.0) it's 16.
- Count in blocks of that size until you pass the address's value in that octet. The block you land in gives the network (its start) and the broadcast (its end, with 255 in the octets after it).
- First and last usable hosts are network + 1 and broadcast − 1.
Host-count questions use 2^(host bits) − 2. Prefix-for-hosts questions add 2 to the host count and round up to the next power of two.
Frequently asked questions
What's the fastest way to subnet?
The block-size method: 256 minus the mask's interesting octet gives the block size; count in blocks to find the network and broadcast. After a few dozen practice questions you can do /24–/30 problems in under 20 seconds.
What subnetting questions come up on the CCNA?
Typically: find the network, broadcast or host range of an address; pick the right mask for a number of hosts or subnets; and check whether two addresses are on the same subnet. The question types here cover all of these.
Do I need to memorise powers of two?
Memorising 2 to 2^12 (2, 4, 8 … 4,096) and the mask values 128, 192, 224, 240, 248, 252, 254, 255 makes subnetting fast. Everything else follows from those.
Are the answers checked strictly?
Spaces, a leading slash and thousands separators are ignored, so /26 and 26 are both accepted for prefix questions, and 4094 matches 4,094. Addresses must be exact.
Can I practise IPv6 subnetting?
The questions are IPv4, which is what exams test in depth. For IPv6, use the IPv6 subnet calculator to split prefixes such as a /48 into /56s and /64s and check your work.