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A small office is expanding and needs proper network segmentation. Your task is to subnet
192.168.10.0/24 to create at least
6 usable subnets
while maximizing hosts per subnet. Assign the first three subnets in order to these departments:
🔵 SALES — needs 25 hosts
🟡 HR — needs 20 hosts
🟠 IT — needs 10 hosts
Subnet Calculator
Base Network (CIDR)
Format: x.x.x.x/prefix (e.g. /24)
Subnets Needed (min 6)
Enter a number between 2 and 128
▶ Calculate Subnets
Borrowed Bits —
New Prefix (CIDR) —
Subnet Mask —
Total Subnets —
Usable Hosts / Subnet —
Block Size (Magic #) —
Binary Mask Visualizer (last octet)
Last octet: 00000000 = 0
Magic Number Reference
Prefix Mask (last oct) Block Usable Hosts Subnets from /24
#
Network ID
Subnet Mask
First Usable
Last Usable
Broadcast
Dept / Role
✓
⚠ Department order error: Sales → Subnet 1, HR → Subnet 2, IT → Subnet 3. Other subnets should be Unused.
💡 Step-by-Step Solution Guide
1. Start with 192.168.10.0/24 . The host portion is 8 bits (last octet).
2. You need ≥6 subnets. Borrowing 3 bits gives 2³ = 8 subnets ✔ (2 bits = only 4 — not enough).
3. New prefix = /24 + 3 = /27 . Subnet mask = 255.255.255.224 . Block size = 2⁵ = 32 . Usable hosts = 30/subnet.
4. All depts fit: Sales needs 25 (≤30 ✔), HR needs 20 (≤30 ✔), IT needs 10 (≤30 ✔).
5. Subnets increment by 32: .0 → .32 → .64 → .96 → .128 → .160 → .192 → .224
6. For each subnet: Network ID = .X, First Usable = .X+1, Last Usable = .X+30, Broadcast = .X+31
7. Assign: Subnet 1 → Sales , Subnet 2 → HR , Subnet 3 → IT , Subnets 4–8 → Unused
Activity Log
00:00:00 Subnetting Lab ready. Base network: 192.168.10.0/24
00:00:00 Enter subnet count → Calculate → Fill table → Grade.
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