Subnetting PBQ Lab 4: Network Address Assigned to Host

Find the workstation that was accidentally assigned the subnet network address.

Scenario

Help Desk Ticket

A branch office uses the subnet 172.16.8.128/28. One device cannot communicate because it was assigned an address that cannot be used by a host.

Network Diagram

🌐

Default Gateway

Router Interface

IP Address: 172.16.8.129

Subnet Mask: 255.255.255.240 (/28)

🖥️

PC-A

IP Address172.16.8.130
Subnet Mask255.255.255.240
Gateway172.16.8.129
Reported: Working
🖥️

PC-B

IP Address172.16.8.134
Subnet Mask255.255.255.240
Gateway172.16.8.129
Reported: Working
🖥️

PC-C

IP Address172.16.8.128
Subnet Mask255.255.255.240
Gateway172.16.8.129
Reported: Not Working
🖥️

PC-D

IP Address172.16.8.140
Subnet Mask255.255.255.240
Gateway172.16.8.129
Reported: Working

Subnet Work Area

ItemStudent Work
CIDR/28
Subnet Mask255.255.255.240
Block Size256 - 240 = ______
Network Address172.16.8.______
Broadcast Address172.16.8.______
Usable Host Range172.16.8.______ through 172.16.8.______

Answer the PBQ

Instructor Answer Key

Bad device: PC-C

Why: 172.16.8.128 is the network address for the 172.16.8.128/28 subnet.

  • Network: 172.16.8.128
  • Broadcast: 172.16.8.143
  • Usable: 172.16.8.129–172.16.8.142
  • Correction: Assign PC-C an unused usable host IP.

Instructor Debrief Script

“The network address identifies the subnet itself. The broadcast address talks to everyone in that subnet. Neither one belongs on a workstation.”

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