Subnetting Practice Questions
Work through these seven questions the way you would in the CCNA exam — cover the answer, solve it with the block-size method, then check. They cover host counting, subnet ranges, VLSM sizing and reverse look-ups.
Questions
Q1. How many subnets and usable hosts does 192.168.1.0/26 give, and what are the subnet ranges?
Show worked answer
/26 → mask 255.255.255.192 → block size 64. Subnets: .0, .64, .128, .192 = 4 subnets, each with 2^6 − 2 = 62 hosts.
.0 hosts .1–.62 bcast .63 .64 hosts .65–.126 bcast .127 .128 hosts .129–.190 bcast .191 .192 hosts .193–.254 bcast .255
Q2. Which subnet does 172.16.20.200/21 belong to? Give the network, broadcast and host range.
Show worked answer
/21 → mask 255.255.248.0 → block size 8 in the 3rd octet. Multiples of 8: 0, 8, 16, 24 … 20 falls in the 16 block (16–23).
Network: 172.16.16.0 First host:172.16.16.1 Last host: 172.16.23.254 Broadcast: 172.16.23.255
Q3. A department needs 50 hosts. What is the smallest subnet that fits?
Show worked answer
Find the smallest host block ≥ 50. 2^5 − 2 = 30 (too small); 2^6 − 2 = 62 (fits). 32 − 6 host bits = /26.
Q4. How many /27 subnets can you make from a single /24?
Show worked answer
2^(27 − 24) = 2^3 = 8 subnets, each with 30 usable hosts.
Q5. Is 10.5.4.130/25 a network address, a usable host, or a broadcast?
Show worked answer
/25 → block 128 in 4th octet → subnets .0 and .128. 130 is in the .128 subnet (host range .129–.254, broadcast .255). So 10.5.4.130 is a usable host address.
Q6. You are given 192.168.10.0/24 and must create 6 equal subnets. What prefix do you use and how many hosts each?
Show worked answer
Need ≥ 6 subnets → 2^3 = 8 ≥ 6, so borrow 3 bits → /27. Each /27 has 2^5 − 2 = 30 hosts. (You get 8 subnets; 2 are spare for growth.)
Q7. What is the network address of 200.100.50.77/28?
Show worked answer
/28 → block 16 in 4th octet. Multiples of 16: 64, 80. 77 falls in the 64 block. Network = 200.100.50.64, broadcast .79, hosts .65–.78.
How to practise effectively
- Do a set of 5–10 every day — subnetting is a speed skill, not a one-time understanding.
- Always solve for all four values: network, first host, last host, broadcast.
- Check every answer against our subnet calculator until your manual answers always match.
- Once you are fast in the 4th octet, practise /17–/23 in the 3rd octet.
Frequently asked questions
How do I get faster at subnetting?
Practise daily with a timer and always solve for all four values (network, first host, last host, broadcast). Speed comes from repetition of the block-size method, not from memorising answers.
How many subnetting questions are on the CCNA?
Cisco does not publish an exact count, but subnetting underpins many routing, addressing and troubleshooting questions. Being fast and accurate helps across the whole exam.
What is VLSM?
Variable Length Subnet Masking means using different prefix lengths for different subnets so each is sized to its host count — saving address space compared with one fixed mask.
Do these answers use the shortcut method?
Yes — every answer uses the block-size (magic-number) method so you can reproduce it in your head under exam time pressure.
Related articles
Want hands-on training?
Learn this on real Cisco lab devices with placement support at Attila Technologies, Ahmedabad.