easyMultiple ChoiceObjective-mapped
300-410 Practice Question: Runs the following command on Router R5: R5# show…
A network engineer runs the following command on Router R5:
R5# show logging | include %LINEPROTO-5-UPDOWN *Mar 1 00:00:10.123: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet0/0, changed state to up *Mar 1 00:00:20.456: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet0/0, changed state to down *Mar 1 00:00:30.789: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet0/0, changed state to up *Mar 1 00:00:40.012: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet0/0, changed state to down *Mar 1 00:00:50.345: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet0/0, changed state to up *Mar 1 00:01:00.678: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet0/0, changed state to down
Based on this output, what is the most likely problem?
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
✓
There is a physical layer issue causing the interface to flap.
The output shows the line protocol on GigabitEthernet0/0 flapping every 10 seconds. This is a classic symptom of a flapping interface, often due to a physical issue (bad cable, faulty transceiver) or a Layer 2 problem (e.g., spanning tree topology changes, keepalive mismatch).
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 interface is administratively down.
Why it's wrong here
The interface is going up and down, not administratively down; that would show a different message.
- ✓
There is a physical layer issue causing the interface to flap.
Why this is correct
Repeated line protocol up/down messages indicate a flapping interface, typically due to physical or Layer 2 issues.
- ✗
The interface is configured with a high bandwidth delay product.
Why it's wrong here
Bandwidth delay product does not cause flapping.
- ✗
The router is experiencing a high CPU load due to routing updates.
Why it's wrong here
High CPU might cause slow processing but not line protocol flapping every 10 seconds.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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