220-1101 Networking Practice Question
A technician is setting up a small office network with 15 computers, a router, and an unmanaged switch. The computers are configured with static IP addresses. After connecting all computers to the switch, the technician notices that some computers can communicate with each other but cannot access the internet. The router's LAN IP is 192.168.1.1 with subnet mask 255.255.255.0. The computers have IP addresses in the range 192.168.1.2-192.168.1.16 with default gateway 192.168.1.1. The technician pings the router from a computer that cannot access the internet, and the ping times out. Which of the following is the MOST likely cause?
⚠ Common exam trap
Watch out — candidates often assume a ping timeout must be caused by a firewall blocking ICMP, but they overlook that a physical layer fault (like a bad cable) would also cause a timeout, and the firewall would not affect other traffic types if the link were functional.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The Ethernet cable connecting the switch to the router is faulty.
The ping from a computer to the router (192.168.1.1) times out, indicating that Layer 3 connectivity to the router is absent. Since the switch is unmanaged and operates at Layer 2, it does not perform VLAN routing or filtering; the most likely cause is a physical or data-link layer issue on the link between the switch and the router, such as a faulty Ethernet cable. A faulty cable would prevent frames from reaching the router, causing the ping timeout and the inability to access the internet.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The switch is not forwarding traffic to the router due to a VLAN mismatch.
Why it's wrong here
A VLAN mismatch requires a managed switch with per-port VLAN assignment or trunking configuration. An unmanaged switch does not process 802.1Q tags and treats all connected devices as being in the same broadcast domain. Since local communication among the 15 computers is working, the switch is forwarding frames correctly, making a VLAN mismatch impossible.
- ✗
The computers are configured with the wrong subnet mask.
Why it's wrong here
The subnet mask 255.255.255.0 correctly defines a /24 network. A misconfigured mask would cause computers to make incorrect on-link versus remote determinations, which would typically break communication between the computers themselves, not just to the router. Because local network sharing works and the mask is correct, this option is invalid.
- ✗
The router's firewall is blocking ICMP traffic.
Why it's wrong here
A firewall rule that drops ICMP would stop ping replies but would not affect TCP-based internet traffic such as HTTP or DNS. The problem reports both ping failure and no internet access, so an ICMP filter would leave internet connectivity intact, contradicting the symptoms. Thus, a firewall ICMP block cannot explain the full set of issues.
- ✓
The Ethernet cable connecting the switch to the router is faulty.
Why this is correct
A faulty Ethernet cable between the switch and the router would prevent any frames from reaching the router, explaining both the ping timeout to the router and the lack of internet access. However, devices connected to the same switch would still communicate directly with each other because that traffic stays within the switch and does not need the cable to the router. This matches all reported symptoms, making it the most plausible cause.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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