Step 7 — Subnetting Practice: Basic
Time to put your skills to work. These problems focus on common /24, /25, /26, and /27 subnets you'll encounter constantly in real networks.
How to use this section:
- Try to solve each problem on paper first
- Write down: network, broadcast, first host, last host, # of hosts
- Check your answer
- If wrong, review the solution carefully
Problem 1: The Classic /24
192.168.10.50/24
Find: Network, Broadcast, First Host, Last Host, Usable Hosts
Show Solution
/24 = 255.255.255.0 → Block size = 256 (entire 4th octet)
| Network | 192.168.10.0 |
| First Host | 192.168.10.1 |
| Last Host | 192.168.10.254 |
| Broadcast | 192.168.10.255 |
| Usable Hosts | 254 |
Problem 2: Splitting in Half
10.0.0.200/25
Find: Network, Broadcast, First Host, Last Host, Usable Hosts
Show Solution
/25 = 255.255.255.128 → Block size = 128
200 falls in the 128-255 block (second half)
| Network | 10.0.0.128 |
| First Host | 10.0.0.129 |
| Last Host | 10.0.0.254 |
| Broadcast | 10.0.0.255 |
| Usable Hosts | 126 |
Problem 3: Four Subnets
172.16.50.100/26
Find: Network, Broadcast, First Host, Last Host, Usable Hosts
Show Solution
/26 = 255.255.255.192 → Block size = 64
Blocks: 0-63, 64-127, 128-191, 192-255
100 falls in the 64-127 block
| Network | 172.16.50.64 |
| First Host | 172.16.50.65 |
| Last Host | 172.16.50.126 |
| Broadcast | 172.16.50.127 |
| Usable Hosts | 62 |
Problem 4: Eight Subnets
192.168.1.75/27
Find: Network, Broadcast, First Host, Last Host, Usable Hosts
Show Solution
/27 = 255.255.255.224 → Block size = 32
Blocks: 0-31, 32-63, 64-95, 96-127, ...
75 falls in the 64-95 block
| Network | 192.168.1.64 |
| First Host | 192.168.1.65 |
| Last Host | 192.168.1.94 |
| Broadcast | 192.168.1.95 |
| Usable Hosts | 30 |
Problem 5: Edge Case - First Block
10.20.30.5/27
Find: Network, Broadcast, First Host, Last Host, Usable Hosts
Show Solution
/27 = 255.255.255.224 → Block size = 32
5 falls in the first block (0-31)
| Network | 10.20.30.0 |
| First Host | 10.20.30.1 |
| Last Host | 10.20.30.30 |
| Broadcast | 10.20.30.31 |
| Usable Hosts | 30 |
Problem 6: Which Subnet?
Two hosts are configured as follows:
- Host A: 192.168.5.65/26
- Host B: 192.168.5.130/26
Can they communicate directly without a router?
Show Solution
/26 = Block size 64
Host A (65) is in block 64-127 → Network: 192.168.5.64
Host B (130) is in block 128-191 → Network: 192.168.5.128
NO - They are on different subnets and need a router!
Problem 7: Design Challenge
You have the network 192.168.100.0/24 and need to create subnets with at least 50 hosts each. What CIDR should you use, and how many subnets will you get?
Show Solution
Need 50 hosts → 2ⁿ - 2 ≥ 50
2⁵ - 2 = 30 (not enough)
2⁶ - 2 = 62 ✓ (enough!)
So we need 6 host bits → 32 - 6 = /26
Answer: Use /26
- 4 subnets (2² = 4, since we borrowed 2 bits from /24)
- 62 usable hosts per subnet
Problem 8: Last Block Edge Case
10.50.100.250/27
Find: Network, Broadcast, First Host, Last Host
Show Solution
/27 = Block size 32
Blocks: 0, 32, 64, 96, 128, 160, 192, 224
250 falls in the 224-255 block (last block)
| Network | 10.50.100.224 |
| First Host | 10.50.100.225 |
| Last Host | 10.50.100.254 |
| Broadcast | 10.50.100.255 |
Checkpoint
You should be able to solve these problems in under 60 seconds each. If you're struggling, go back and review the block size method in Step 5.
Ready for harder problems? Move on to the next step!