220-1101 Networking Practice Question
A technician sets up a small office network using two unmanaged switches to connect 25 computers. After connecting both switches to the router, the network becomes extremely slow and many computers lose connectivity intermittently. The technician notices that the router's status lights on all ports are flashing rapidly. Which of the following is the MOST likely cause of this issue?
⚠ Common exam trap
CompTIA often tests the concept that unmanaged switches lack STP, so candidates may mistakenly think the issue is a faulty router or DHCP problem, overlooking the classic symptom of rapid port flashing caused by a broadcast storm from a network loop.
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
✓
A broadcast storm caused by a network loop
When two unmanaged switches are connected to the same router without any loop-prevention mechanism (such as STP), broadcast frames forwarded by one switch can be received and re-forwarded by the other, creating a network loop. This causes a broadcast storm, where broadcast frames circulate endlessly, saturating the network bandwidth and causing the router's ports to flash rapidly due to the high traffic load. The resulting congestion leads to extreme slowness and intermittent connectivity loss for all devices.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
A faulty router causing packet loss
Why it's wrong here
A faulty router can certainly cause packet loss and slow throughput, but it would not normally produce the simultaneous rapid flashing of every port light on the device. That symptom indicates a layer 2 broadcast storm flooding the entire broadcast domain, whereas router faults typically manifest as asymmetric or dropped traffic without generating continuous frames on all interfaces. Additionally, the issue is described as occurring in a network of two unmanaged switches, where the router is not the forwarding device for local broadcast traffic.
- ✓
A broadcast storm caused by a network loop
Why this is correct
When two unmanaged switches are connected by more than one cable, a physical network loop is created. Because unmanaged switches do not implement Spanning Tree Protocol (STP), broadcast frames are forwarded out every port and then re-received, causing them to endlessly circulate and multiply exponentially. This broadcast storm saturates the switch fabric and all attached links, which is why every port light on the router (and switches) flashes rapidly at the same time. The result is a complete loss of usable connectivity across the network, matching the technician's observation.
- ✗
DNS server misconfiguration
Why it's wrong here
DNS server misconfiguration would prevent name resolution, so users might be unable to reach websites by hostname, but the underlying network would still function normally for IP-based traffic. It would not cause intermittent loss of connectivity or a sudden burst of activity on all router port lights simultaneously. The physical-layer symptoms described point to continuous frame flooding, not a failure to translate domain names to IP addresses. Moreover, DNS problems typically produce consistent errors, not the chaotic, network-wide saturation seen here.
- ✗
Incorrect DHCP scope size
Why it's wrong here
Incorrect DHCP scope size could cause some devices to fail to obtain an IP address when the pool is exhausted, but it would not explain widespread loss of connectivity or the rapid flashing of all router port lights. Once a client has an IP address, the DHCP server is no longer involved in its ongoing traffic, so existing connections would remain stable even if the scope is wrong. The symptom of all ports flashing simultaneously indicates a data-plane storm (like a broadcast loop), not a control-plane issue with address allocation. DHCP errors would also affect only new connections, not cause a total network meltdown.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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