CCNA Subnetting Practice
NetExam Pro · Timed drills · Exam-style questions · Free subnet calculator
Subnetting is where CCNA candidates lose the most marks
It's also the most trainable skill on the exam. Ten focused hours of subnetting drills will do more for your score than ten hours of re-reading theory. NetExam Pro gives you exam-style subnetting questions, timed drills, and a free subnet calculator to check your work.
- Exam-style subnetting questions — block sizes, broadcast addresses, VLSM, summarisation
- Timed drills — the exam gives you ~60 seconds per question; practice at that pace
- Full explanations — every answer shows the working, not just the result
- Free tools: subnet calculator and subnetting cheat sheet
Try these subnetting questions
Network Fundamentals
What is the default (classful) subnet mask of a Class B IPv4 address?
- 255.0.0.0
- 255.255.0.0
- 255.255.255.0
- 255.255.255.255
Show answer & explanation
Answer: 255.255.0.0
Class B addresses (128.0.0.0–191.255.255.255) default to a /16 mask: 255.255.0.0. Class A defaults to /8 (255.0.0.0) and Class C to /24 (255.255.255.0). Note that classful addressing is obsolete in practice, but the defaults are still tested.
Network Fundamentals
The network 192.168.10.0/24 must be subnetted so that each subnet supports at least 30 hosts. Which subnet mask meets the requirement with the least address waste?
- 255.255.255.128 (/25)
- 255.255.255.192 (/26)
- 255.255.255.224 (/27)
- 255.255.255.240 (/28)
Show answer & explanation
Answer: 255.255.255.224 (/27)
A /27 leaves 5 host bits: 2^5 - 2 = 30 usable hosts, exactly meeting the requirement. A /28 gives only 14 hosts (too few), while /25 and /26 give 126 and 62 hosts respectively — both work but waste far more addresses than /27.
Network Fundamentals
What is the broadcast address of the subnet 172.16.44.0/22? Enter the full dotted-decimal address.
Type your answer, then reveal the solution below.
Show answer & explanation
Answer: 172.16.47.255
A /22 borrows 6 bits of the third octet, so subnets increment by 4 in the third octet: 172.16.44.0 covers 172.16.44.0–172.16.47.255. The broadcast address is the last address in the range: 172.16.47.255.
The 30-second subnetting method
For most CCNA subnetting questions you only need one formula: block size = 256 − mask octet. A /27 mask means a block size of 32 — subnets step in multiples of 32 (0, 32, 64, 96…). Usable hosts = 2n − 2, where n is the number of host bits. Drill this until it's automatic; on exam day it should take under 30 seconds per question. Our cheat sheet covers VLSM and route summarisation too.